THE DISTRIBUTION OF FRESHWATER FISHES.
Having shown above that numerous marine fishes enter fresh waters, and
that some of them have permanently established themselves therein,
we have to eliminate from the category of freshwater fishes all such
adventitious elements. They are derived from forms, the distribution
of which is regulated by other agencies, and which, therefore, would
obscure the relations of the faunæ of terrestrial regions if they were
included in them. They will be mentioned with greater propriety along
with the fishes constituting the fauna of the brackish water.
True freshwater fishes are the following families and groups only:--
Dipnoi with 4 species.
Acipenseridæ and
Polyodontidæ „ 26 „
Amiidæ „ 1 „
Polypteridæ. „ 2 „
Lepidosteidæ. „ 3 „
Percina „ 46 „
Grystina „ 11 „
Aphredoderidæ „ 1 „
Centrarchina „ 26 „
Dules „ 10 „
Nandidæ „ 7 „
Polycentridæ „ 3 „
Labyrinthici „ 30 „
Luciocephalidæ „ 1 „
Gastrosteus „ 10 „
Ophiocephalidæ „ 31 „
Mastacembelidaæ „ 13 „
Chromides „ 105 „
Comephoridæ „ 1 „
Gadopsidæ „ 1 „
Siluridæ „ 572 „
Characinidæ „ 261 „
Haplochitonidæ „ 3 „
Salmonidæ (3 genera
excepted) „ 135 „
Percopsidæ „ 1 „
Galaxiidæ „ 15 „
Mormyridæ (and
Gymnarchidæ) „ 52 „
Esocidæ „ 8 „
Umbridæ „ 2 „
Cyprinodontidæ „ 112 „
Heteropygii „ 2 „
Cyprinidæ „ 724 „
Kneriidæ „ 2 „
Hyodontidæ „ 1 „
Osteoglossidæ „ 5 „
Notopteridæ „ 5 „
Gymnotidæ „ 20 „
Symbranchidæ „ 5 „
Petromyzontidæ „ 12 „
--------------
Total 2269 species.
==============
As in every other class of animals, these freshwater genera and
families vary greatly with regard to the extent of their geographical
range; some extend over the greater half of the continental areas,
whilst others are limited to one continent only, or even to a very
small portion of it. As a general rule, a genus or family of freshwater
fishes is regularly dispersed and most developed within a certain
district, the species and individuals becoming scarcer towards the
periphery as the type recedes more from its central home, some outposts
being frequently pushed far beyond the outskirts of the area occupied
by it. But there are not wanting those remarkable instances of closely
allied forms occurring, almost isolated, at most distant points,
without being connected by allied species in the intervening space;
or of members of the same family, genus, or species inhabiting the
opposite shores of an ocean, and separated by many degrees of abyssal
depths. We mention of a multitude of such instances the following
only:--
_A_. Species identical in distant continents--
1. A number of species inhabiting Europe and the temperate parts of
eastern North America, as _Perca fluviatilis_, _Gastrosteus pungitius_,
_Lota vulgaris_, _Salmo solar_, _Esox lucius_, _Acipenser sturio_,
_Acipenser maculosus_, and several Petromyzonts.
2. _Lates calcarifer_ is common in India as well as in Queensland.
3. _Galaxias attenuatus_ inhabits Tasmania, New Zealand, the Falkland
Islands, and the southernmost part of the South American continent.
4. Several Petromyzonts enter the fresh waters of Tasmania, South
Australia, New Zealand, and Chili.
_B._ Genera identical in distant continents--
1. The genus _Umbra_, so peculiar a form as to be the type of a
distinct family consisting of two most closely allied species only, one
of which is found in the Atlantic States of North America, the other in
the system of the Danube.
2. A very distinct genus of Sturgeons, _Scaphirhynchus_, consisting
of two species only, one inhabiting fresh waters of Central Asia, the
other the system of the Mississippi.
3. A second most peculiar genus of Sturgeons, _Polyodon_, consists
likewise of two species only, one inhabiting the Mississippi, the other
the Yang-tse-kiang.
4. _Amiurus_, a Siluroid, and _Catostomus_, a Cyprinoid genus, both
well represented in North America, occur in a single species in
temperate China.
5. _Lepidosiren_ is represented by one species in tropical America, and
by the second in tropical Africa (_Protopterus_).
6. _Notopterus_ consists of three Indian and two West African species.
7. _Mastacembelus_ and _Ophiocephalus_, genera characteristic of the
Indian region, emerge severally by a single species in West and Central
Africa.
8. _Symbranchus_ has two Indian and one South American species.
9. _Prototroctes_, the singular antarctic analogue of _Coregonus_,
consists of two species, one in the south of Australia the other in New
Zealand.
10. _Galaxias_ is equally represented in Southern Australia, New
Zealand, and the southern parts of South America.
_C._ Families identical in distant continents--
1. The _Labyrinthici_, represented in Africa by 5, and in India by
25 species.
2. The _Chromides_, represented in Africa by 25, and in South
America by 80 species.
3. The _Characinidæ_, represented in Africa by 35, and in South
America by 226 species.
4. The _Haplochitonidæ_, represented in Southern Australia by one,
in New Zealand by one, and in Patagonia by a third species.
This list could be much increased from the families of _Siluridæ_
and _Cyprinidæ_, but as these have a greater range than the other
Freshwater fishes, they do not illustrate with equal force the object
for which the list has been composed.
* * * * *
The ways in which the dispersal of Freshwater fishes has been effected
were various; they are probably all still in operation, but most work
so slowly and imperceptibly as to escape direct observation; perhaps,
they will be more conspicuous, after science and scientific inquiry
shall have reached to a somewhat greater age. From the great number
of freshwater forms which we see at this present day acclimatised in,
gradually acclimatising themselves in, or periodically or sporadically
migrating into, the sea, we must conclude that, under certain
circumstances, salt water may cease to be an impassable barrier at some
period of the existence of freshwater species, and that many of them
have passed from one river through salt water into another. Secondly,
the headwaters of some of the grandest rivers, the mouths of which are
at opposite ends of the continents which they drain, are sometimes
distant from each other a few miles only; the intervening space may
have been easily bridged over for the passage of fishes by a slight
geological change affecting the level of the watershed, or even by
temporary floods; and a communication of this kind, if existing for a
limited period only, would afford the ready means of an exchange of
a number of species previously peculiar to one or the other of those
river or lake systems. Some fishes, provided with gill-openings so
narrow that the water moistening the gills cannot readily evaporate;
and endowed, besides, with an extraordinary degree of vitality, like
many Siluroids (_Clarias_, _Callichthys_), Eels, etc., are enabled to
wander for some distance over land, and may thus reach a water-course
leading them thousands of miles from their original home. Finally,
fishes or their ova may be accidentally carried by waterspouts, by
aquatic birds or insects, to considerable distances.
Freshwater fishes of the present fauna were already in existence when
the great changes of the distribution of land and water took place
in the tertiary epoch; and having stated that salt water is not an
absolute barrier to the spreading of Freshwater fishes, we can now
more easily account for those instances of singular disconnection of
certain families or genera. It is not necessary to assume that there
was a continuity of land stretching from the present coast of Africa
to South America, or from South America to New Zealand and Australia,
to explain the presence of identical forms at so distant localities;
it suffices to assume that the distances were lessened by intervening
archipelagoes, or that an oscillation has taken place in the level of
the land area.
Dispersal of a type over several distant continental areas may be
evidence of its great antiquity, but it does not prove that it is of
greater antiquity than another limited to one region only. Geological
evidence is the only proof of the antiquity of a type. Thus, although
the _Dipnoi_ occur on the continents of Africa, South America, and
Australia, and their present distribution is evidently the consequence
of their wide range in palæozoic and secondary epochs; the proof
of their high antiquity can be found in their fossil remains only.
For, though the Siluroids have a still greater range, their wide
distribution is of comparatively recent date, as the few fossil remains
that have been found belong to the tertiary epoch. The rapidity of
dispersal of a type depends entirely on its facility to accommodate
itself to a variety of physical conditions, and on the degree of
vitality by which it is enabled to survive more or less sudden changes
under unfavourable conditions; proof of this is afforded by the family
of Siluroids, many of which can suspend for some time the energy of
their respiratory functions, and readily survive a change of water.
* * * * *
To trace the geological sequence of the distribution of an ichthyic
type, and to recognise the various laws which have governed, and
are still governing its dispersal, is one of the ultimate tasks of
Ichthyology. But the endeavour to establish by means of our present
fragmentary geological knowledge the divisions of the fauna of the
globe, leads us into a maze of conflicting evidence; or, as Mr.
Wallace truly observes, “any attempt to exhibit the regions of former
geological ages in combination with those of our own period must lead
to confusion.” Nevertheless, as the different types of animals found
at the present day within a particular area have made their appearance
therein at distant periods, we should endeavour to decide as far as
we can, in an account of the several zoo-geographical divisions, the
following questions:--
1. Which of the fishes of an area should be considered to be the
remnants of _ancient_ types, probably spread over much larger areas in
preceding epochs?
2. Which of them are to be considered to be _autochthont_ species,
that is, forms which came in the tertiary epoch or later into existence
within the area to which they are still limited, or from which they
have since spread?
3. Which are the forms which must be considered to be _immigrants_
from some other region?
The mode of division of the earth’s surface into zoological regions
or areas now generally adopted, is that proposed by Mr. Sclater,
which recommends itself as most nearly agreeing with the geographical
divisions. These regions are as follows:--
I. PALÆOGÆA.
1. The _Palæarctic_ region; including Europe, temperate Asia,
and North Africa.
2. The _Ethiopian_ region; including Africa, south of the
Sahara, Madagascar, and the Mascarene Islands; also
Southern Arabia.
3. The _Indian_ region; including India south of the
Himalayas, to Southern China, Borneo, and Java.
4. The _Australian_ region; including Australia, the
Pacific Islands, Celebes, and Lombock.
II. NEOGÆA.
5. The _Nearctic_ region; including North America to
Northern Mexico.
6. The _Neotropical_ region; including South America, the West
Indies, and Southern Mexico.
Comparatively few classes and orders of animals have been carefully
studied with regard to their geographical distribution, but the
majority of those which have been examined show that the difference
of latitude is accompanied by a greater dissimilarity of indigenous
species than that of longitude, and that a main division into an old
world and new world fauna is untenable. More especially the Freshwater
fishes, with which we are here solely concerned, have been spread in
_circumpolar_ zones, and in a but limited degree from north to
south. No family, much less a genus, ranges from the north to the
south, whilst a number of families and genera make the entire circuit,
and some species more than half of the circuit round the globe within
the zone to which they belong. Not even the Cyprinoids and Siluroids,
which are most characteristic of the freshwater fauna of our period,
are an exception to this. Temperature and climate, indeed, are the
principal factors by which the character of the freshwater fauna is
determined; they form the barriers which interfere with the unlimited
dispersal of an ichthyic type, much more than mountain ranges, deserts,
or oceans. Hence the tropical zone is an impassable barrier to the
northern Freshwater fish in its progress towards the south; where
a similarly temperate climate obtains in the southern hemisphere,
fish-forms appear _analogous_ to those of the north, but
_genetically_ and _structurally distinct_.
The similarity which obtains in fishes at somewhat distant points
of the same degree of longitude, rarely extends far, and is due to
the natural tendency of every animal to spread as far as physical
conditions will permit. Between two regions situated north and south
of each other there is always a debateable border ground, in parts of
which sometimes the fishes of the one, sometimes those of the other,
predominate, and which is, in fact, a _band_ of demarcation. Within
this band the regions overlap each other; therefore, their border
_lines_ are rarely identical, and should be determined by the northern
and southernmost extent of the most characteristic types of each
region. Thus, for instance, in China, a broad band intervenes between
temperate and tropical Asia, in which these two faunæ mix, and the
actual northern border line of the tropical fauna is north of the
southern border line of temperate Asia.
It is the aim of every philosophical classification to indicate the
degree of affinity which obtains between the various divisions; but
the mode of division into six equivalent regions, as given above, does
not fulfil this aim with regard to Freshwater fishes, the distribution
of which allows of further generalisation and subdivision. The two
families, _Cyprinidæ_ and _Siluridæ_, of which the former yields a
contingent of one-third, and the latter of one-fourth of all the
freshwater species known of our period, afford most valuable guidance
for the valuation of the degrees of affinity between the various
divisions. The Cyprinoids may be assumed to have taken their origin
in the Alpine region, dividing the temperate and tropical parts of
Asia; endowed with a greater capability of acclimatising themselves
in a temperate as well as tropical climate than any other family of
freshwater fishes, they spread north and south as well as east and
west; in the preglacial epoch they reached North America, but they have
not had time to penetrate into South America, Australia, or the islands
of the Pacific. The Siluroids, principally fishes of the sluggish
waters of the plains, and well adapted for surviving changes of the
water in which they live, for living in mud or sea-water, flourish
most in the tropical climate, in which this type evidently had its
origin. They came into existence after the Cyprinoids, fossil remains
being known only from tertiary deposits in India, none from Europe.
They rapidly spread over the areas of land within the tropical zone,
reaching northern Australia from India, and one species even immigrated
into the Sandwich Islands, probably from South America. The Coral
Islands of the Pacific still remain untenanted by them. Their progress
into temperate regions was evidently slow, only very few species
penetrating into the temperate parts of Asia and Europe; and the North
American species, although more numerous, showing no great variety
of structure, all belonging to the same group (_Amiurina_). Towards
the south their progress was still slower, Tasmania, New Zealand, and
Patagonia being without representatives, whilst the streams of the
Andes of Chili are inhabited by a few dwarfed forms identical with such
as are characteristic of similar localities in the more northern and
warmer parts of the South American continent.
After these preliminary remarks we propose the following division of
the fauna of Freshwater fishes:--
I. THE NORTHERN ZONE.--Characterised by Acipenseridæ. Few
Siluridæ. Numerous Cyprinidæ. Salmonidæ, Esocidæ.
1. _Europo-Asiatic or Palæarctic Region_.--Characterised by
absence of osseous Ganoidei; Cobitidæ and Barbus numerous.
2. _North American Region_.--Characterised by osseous Ganoidei,
Amiurina, and Catostomina; but no Cobitidæ or Barbus.
II. THE EQUATORIAL ZONE.--Characterised by the development of
Siluridæ.
A. _Cyprinoid Division_.--Characterised by presence of Cyprinidæ
and Labyrinthici.
1. _Indian Region_.--Characterised by [absence of Dipnoi[18]]
Ophiocephalidæ, Mastacembelidæ. Cobitidæ numerous.
2. _African Region_.--Characterised by presence of Dipnoi and
Polypteridæ. Chromides and Characinidæ numerous. Mormyridæ.
Cobitidæ absent.
B. _Acyprinoid Division_.--Characterised by absence of Cyprinidæ
and Labyrinthici.
1. _Tropical American Region_.--Characterised by presence of
Dipnoi. Chromides and Characinidæ numerous. Gymnotidæ.
2. _Tropical Pacific Region_.--Characterised by presence of
Dipnoi. Chromides and Characinidæ absent.
III. THE SOUTHERN ZONE.--Characterised by absence of Cyprinidæ, and
scarcity of Siluridæ. Haplochitonidæ and Galaxiidæ represent
the Salmonoids and Esoces of the Northern zone. One region
only.
1. _Antarctic Region_.--Characterised by the small number of
species; the fishes of--
_a_. The Tasmanian sub-region;
_b_. The New Zealand sub-region;
_c_. The Patagonian sub-region;
being almost identical.[19]
In the following detailed account we begin with a description of the
equatorial zone, this being the one from which the two principal
families of freshwater fishes seem to have spread.
I. EQUATORIAL ZONE.
Roughly speaking, the borders of this zoological zone coincide with
the geographical limits of the tropical zone, the tropics of the
Cancer and Capricorn; its characteristic forms, however, extend in
undulating lines several degrees north and southwards. Commencing from
the west coast of Africa the desert of the Sahara forms a well-marked
boundary between the equatorial and northern zones; as the boundary
approaches the Nile it makes a sudden sweep towards the north as far
as Northern Syria (_Mastacembelus_, near Aleppo, and in the Tigris;
_Clarias_ and _Chromides_, in the lake of Galilee); crosses through
Persia and Afghanistan (_Ophiocephalus_), to the southern ranges of the
Himalayas, and follows the course of the Yang-tse-Kiang, which receives
its contingent of equatorial fishes through its southern tributaries.
Its continuation through the North Pacific may be considered to be
indicated by the tropic which strikes the coast of Mexico at the
southern end of the Gulf of California. Equatorial types of South
America are known to extend so far northwards; and by following the
same line the West India Islands are naturally included in this zone.
Towards the south the equatorial zone embraces the whole of Africa
and Madagascar, and seems to extend still farther south in Australia,
its boundary probably following the southern coast of that continent;
the detailed distribution of the freshwater fishes of South-Western
Australia has been but little studied, but the few facts which we
know show that the tropical fishes of Queensland follow the principal
water-course of that country, the Murray River, far towards the
south and probably to its mouth. The boundary-line then stretches
northwards of Tasmania and New Zealand, coinciding with the tropic
until it strikes the western slope of the Andes, on the South American
Continent, where it again bends southwards to embrace the system of the
Rio de la Plata.
The equatorial zone is divided into four regions:--
A. The Indian region.
B. The African region.
C. The Tropical American region.
D. The Tropical Pacific region.
These four regions diverge into two well-marked divisions, one of
which is characterised by the presence of Cyprinoid fishes, combined
with the development of Labyrinthici; whilst in the other both these
types are absent. The boundary between the Cyprinoid and Acyprinoid
division seems to follow Wallace’s line, a line drawn from the south of
the Philippines between Borneo and Celebes, and farther south between
Bali and Lombock. Borneo abounds in Cyprinoids; from the Philippine
Islands a few only are known at present, and in Bali two species have
been found; but none are known from Celebes or Lombock, or from islands
situated farther east of them.[20]
Taking into consideration the manner in which Cyprinoids and Siluroids
have been dispersed, we are obliged to place the Indian region as
the first in the order of our treatment; and indeed the number of
its freshwater fishes, which appear to have spread from it into the
neighbouring regions, far exceeds that of the species which it has
received from them.
* * * * *
A. The INDIAN REGION comprises the whole continent of Asia south of
the Himalayas and the Yang-tse-kiang; it includes the islands to
the west of Wallace’s line. Towards the north-east the island of
Formosa, which also by other parts of its fauna leans more towards the
equatorial zone, has received some characteristic Japanese Freshwater
fishes, for instance, the singular Salmonoid _Plecoglossus_. Within
the geographical boundaries of China the Freshwater fishes of the
tropics pass gradually into those of the northern zone, both being
separated by a broad debateable ground. The affluents of the great
river traversing this district are more numerous from the south than
from the north, and carry the southern fishes far into the temperate
zone. The boundary of this region towards the north-west is scarcely
better defined. Before Persia passed through the geological changes
by which its waters were converted into brine and finally dried
up, it seems to have been inhabited by many characteristic Indian
forms, of which a few still survive in the tract intervening between
Afghanistan and Syria; _Ophiocephalus_ and _Discognathus_ have each
at least one representative, _Macrones_ has survived in the Tigris,
and Mastacembelus has penetrated as far as Aleppo. Thus, Freshwater
fishes belonging to India, Africa, and Europe, are intermingled in a
district which forms the connecting link between the three continents.
Of the freshwater fishes of Arabia we are perfectly ignorant; so much
only being known that the Indian _Discognathus lamta_ occurs in the
reservoirs of Aden, having, moreover, found its way to the opposite
African coast; and that the ubiquitous Cyprinodonts flourish in
brackish pools of Northern Arabia.
The following is the list of the forms of freshwater fishes inhabiting
this region:[21]--
Percina--
Lates[22] [Africa, Australia] 1 species.
_Nandina_ 7 „
Labyrinthici [Africa] 25 „
_Luciocephalidæ_ 1 „
_Ophiocephalidæ_ [1 species in Africa] 30 „
_Mastacembelidæ_ [3 species in Africa] 10 „
Chromides [Africa, South America]
_Etroplus_ 2 „
Siluridæ--
Clariina [Africa] 12 „
_Chacina_ 3 „
Silurina [Africa, Palæarct.] 72 „
Bagrina [Africa] 50 „
Ariina [Africa, Australia, South America] 40 „
_Bagariina_ 20 „
Rhinoglanina [Africa] 1 „
Hypostomatina [South America] 5 „
Cyprinodontidæ--
Carnivoræ [Palæarct., North America,
Africa, South America]
Haplochilus [Africa, South America,
North America, Japan] 4 „
Cyprinidæ [Palæarct., N. America, Africa]--
Cyprinina [Palæarct., N. America, Africa] 190 „
_Rasborina_ [Africa, 1 species] 20 „
_Semiplotina_ 4 „
Danionina [Africa] 30 „
Abramidina [Palæarct., N. Amer., Africa] 30 „
_Homalopterina_ 10 „
Cobitidina [Palæarct.] 50 „
Osteoglossidæ [Africa, Australia, S. America] 1 „
Notopteridæ [Africa] 3 „
Symbranchidæ--
_Amphipnous_ 1 „
_Monopterus_ 1 „
Symbranchus [1 species in S. America] 2 „
------------
625 species.
============
In analysing this list we find that out of 39 families or groups of
freshwater fishes 12 are represented in this region, and that 625
species are known to occur in it; a number equal to two-sevenths of
the entire number of freshwater fishes known. This large proportion
is principally due to the development of numerous local forms of
Siluroids and Cyprinoids, of which the former show a contingent
of about 200, and the latter of about 330 species. The combined
development of those two families, and their undue preponderance over
the other freshwater types, is therefore the principal characteristic
of the Indian region. The second important character of its fauna is
the apparently total absence of Ganoid and Cyclostomous fishes. Every
other region has representatives of either Ganoids or Cyclostomes,
some of both. However, attention has been directed to the remarkable
coincidence of the geographical distribution of the _Sirenidæ_
and _Osteoglossidæ_, and as the latter family is represented in
Sumatra and Borneo, it may be reasonably expected that a Dipnoous form
will be found to accompany it. The distribution of the _Sirenidæ_
and _Osteoglossidæ_ is as follows:--
_Tropical America._
Lepidosiren paradoxa. | Osteoglossum bicirrhosum.
| Arapaima gigas.
_Tropical Australia._
Ceratodus forsteri. | Osteoglossum leichardti.
Ceratodus miolepis.
_East Indian Archipelago._
? | Osteoglossum formosum.
_Tropical Africa._
Protopterus annectens. | Heterotis niloticus.
Not only are the corresponding species found within the same region,
but also in the same river systems; and although such a connection
may and must be partly due to a similarity of habit, yet the identity
of this singular distribution is so striking that it can only be
accounted for by assuming that the _Osteoglossidæ_ are one of the
earliest Teleosteous types which have been contemporaries of and have
accompanied the present Dipnoi since or even before the beginning of
the tertiary epoch.
Of the _autochthont_ freshwater fishes of the Indian region, some
are still limited to it, viz., the _Nandina_, the _Luciocephalidæ_
(of which one species only exists in the Archipelago), of Siluroids
the _Chacina_ and _Bagariina_, of Cyprinoids the _Semiplotina_ and
_Homalopterina_; others very nearly so, like the _Labyrinthici_,
_Ophiocephalidæ_, _Mastacembelidæ_, of Siluroids the _Silurina_, of
Cyprinoids the _Rasborina_ and _Danionina_, and _Symbranchidæ_.
The regions with which the Indian has least similarity are the North
American and Antarctic, as they are the most distant. Its affinity to
the other regions is of a very different degree:--
1. Its affinity to the Europo-Asiatic region is indicated almost solely
by three groups of Cyprinoids, viz., the _Cyprinina_, _Abramidina_,
and _Cobitidina_. The development of these groups north and south of
the Himalayas is due to their common origin in the highlands of Asia;
but the forms which descended into the tropical climate of the south
are now so distinct from their northern brethren that most of them are
referred to distinct genera. The genera which are still common to both
regions are only the true Barbels (_Barbus_), a genus which, of all
Cyprinoids, has the largest range over the old world, and of which some
160 species have been described; and, secondly, the Mountain Barbels
(_Schizothorax_, etc.), which, peculiar to the Alpine waters of Central
Asia, descend a short distance only towards the tropical plains, but
extend farther into rivers within the northern temperate districts. The
origin and the laws of the distribution of the _Cobitidina_ appear to
have been identical with those of _Barbus_, but they have not spread
into Africa.
If, in determining the degree of affinity between two regions, we take
into consideration the extent in which an exchange has taken place of
the faunæ originally peculiar to each, we must estimate that obtaining
between the freshwater fishes of the Europo-Asiatic and Indian regions
as very slight indeed.
2. There exists a great affinity between the Indian and African
regions; seventeen out of the twenty-six families or groups found in
the former are represented by one or more species in Africa, and many
of the African species are not even generically different from the
Indian. As the majority of these groups have many more representatives
in India than in Africa, we may reasonably assume that the African
species have been derived from the Indian stock; but this is probably
not the case with the Siluroid group of _Clariina_, which with regard
to species is nearly equally distributed between the two regions,
the African species being referable to three genera (_Clarias_,
_Heterobranchus_, _Gymnallabes_, with the subgenus _Channallabes_),
whilst the Indian species belong to two genera only, viz. _Clarias_
and _Heterobranchus_. On the other hand, the Indian region has derived
from Africa one freshwater form only, viz. _Etroplus_, a member of the
family of _Chromides_, so well represented in tropical Africa and South
America. _Etroplus_ inhabits Southern and Western India and Ceylon, and
has its nearest ally in a Madegasse Freshwater fish, _Paretroplus_.
Considering that other African Chromides have acclimatised themselves
at the present day in saline water, we think it more probable that
Etroplus should have found its way to India through the ocean than over
the connecting land area; where, besides, it does not occur.
3. A closer affinity between the Indian and Tropical American regions
than is indicated by the character of the equatorial zone generally,
does not exist. No genus of Freshwater fishes occurs in India and South
America without being found in the intermediate African region, with
two exceptions. Four small Indian Siluroids (_Sisor_, _Erethistes_,
_Pseudecheneis_, and _Exostoma_) have been referred to the South
American _Hypostomatina_; but it remains to be seen whether this
combination is based upon a sufficient agreement of their internal
structure, or whether it is not rather artificial. On the other hand,
the occurrence and wide distribution in tropical America of a fish of
the Indian family Symbranchidæ (_Symbranchus marmoratus_), which is
not only congeneric with, but also most closely allied to, the Indian
_Symbranchus bengalensis_, offers one of those extraordinary anomalies
in the distribution of animals of which no satisfactory explanation can
be given at present.
4. The relation of the Indian region to the Tropical Pacific region
consists only in its having contributed a few species to the poor fauna
of the latter. This immigration must have taken place within a recent
period, because some species now inhabit fresh waters of tropical
Australia and the South Sea Islands without having in any way changed
their specific characters, as _Lates calcarifer_, species of _Dules_,
_Plotosus anguillaris_; others (species of _Arius_) are but little
different from Indian congeners. All these fishes must have migrated
by the sea; a supposition which is supported by what we know of their
habits. We need not add that India has not received a single addition
to its freshwater fish-fauna from the Pacific region.
Before concluding these remarks on the Indian region, we must mention
that peculiar genera of Cyprinoids and Siluroids inhabit the streams
and lakes of its alpine ranges in the north. Some of them, like the
Siluroid genera _Glyptosternum_, _Euglyptosternum_, _Pseudecheneis_,
have a folded disk on the thorax between their horizontally spread
pectoral fins; by means of this they adhere to stones at the bottom of
the mountain torrents, and without it they would be swept away into
the lower courses of the rivers. The Cyprinoid genera inhabiting
similar localities, and the lakes into which the alpine rivers pass,
such as _Oreinus_, _Schizothorax_, _Ptychobarbus_, _Schizopygopsis_,
_Diptychus_, _Gymnocypris_, are distinguished by peculiarly enlarged
scales near the vent, the physiological use of which has not yet been
ascertained. These alpine genera extend far into the Europo-Asiatic
region, where the climate is similar to that of their southern home.
No observations have been made by which the altitudinal limits of fish
life in the Himalayas can be fixed, but it is probable that it reaches
the line of perpetual snow, as in the European Alps which are inhabited
by Salmonoids. Griffith found an _Oreinus_ and a Loach, the former in
abundance, in the Helmund at Gridun Dewar, altitude 10,500 feet; and
another Loach at Kaloo at 11,000 feet.
* * * * *
B. THE AFRICAN REGION comprises the whole of the African continent
south of the Atlas and the Sahara. It might have been conjectured that
the more temperate climate of its southern extremity would have been
accompanied by a conspicuous difference of the fish-fauna. But this is
not the case; the difference between the tropical and southern parts
of Africa consists simply in the gradual disappearance of specifically
tropical forms, whilst Siluroids, Cyprinoids, and even Labyrinthici
penetrate to its southern coast; no new form has entered to impart
to South Africa a character distinct from the central portion of the
continent. In the north-east the African fauna passes the Isthmus of
Suez and penetrates into Syria; the system of the Jordan presenting
so many African types that it has to be included in a description of
the African region as well as of the Europo-Asiatic. This river is
inhabited by three species of _Chromis_, one of _Hemichromis_, and
_Clarias macracanthus_, a common fish of the Upper Nile. This infusion
of African forms cannot be accounted for by any one of those accidental
means of dispersal, as _Hemichromis_ is not represented in the
north-eastern parts of Africa proper, but chiefly on the west coast and
in the Central African lakes.
Madagascar clearly belongs to this region. Besides some Gobies and
_Dules_, which are not true freshwater fishes, four _Chromides_ are
known. To judge from general accounts, its Freshwater fauna is poorer
than might be expected; but, singular as it may appear, collectors
have hitherto paid but little attention to the Freshwater fishes of
this island. The fishes found in the freshwaters of the Seychelles
and Mascarenes are brackish-water fishes, such as _Fundulus_,
_Haplochilus_, _Elops_, _Mugil_, etc.
The following is the list of the forms of Freshwater fishes inhabiting
this region:--
Dipnoi [Australia, Neotrop.]--
_Lepidosiren annectens_ 1 species.
_Polypteridæ_ 2 „
Percina (Cosmopol.)--
Lates [India, Australia] 1 „
Labyrinthici [India] 5 „
Ophiocephalidæ [India] 1 „
Mastacembelidæ [India] 3 „
Chromides [South America]--
_Chromis_ 23 „
_Hemichromis_ 5 „
_Paretroplus_ 1 „
Siluridæ--
Clariina [India] 14 „
Silurina [India, Palæarct.] 11 „
Bagrina [India] 10 „
Pimelodina [South America] 2 „
Ariina[23] [India, Australia, S. Amer., Patagonia] 4 „
Doradina [South America]--
_Synodontis_ 15 „
Rhinoglanina [India] 2 „
_Malapterurina_ 3 „
Characinidæ [South America]--
_Citharinina_ 2 „
_Nannocharacina_ 2 „
Tetragonopterina--
_Alestes_ 14 „
Crenuchina--
_Xenocharax_ 1 „
Hydrocyonina--
_Hydrocyon_ 4 „
_Distichodontina_ 10 „
_Ichthyborina_ 2 „
_Mormyridæ_ (_Gymnarchidæ_) 51 „
Cyprinodontidæ--
Carnivoræ [Palæarct., India, S. America--
Haplochilus [India, South America] 7 „
Fundulus [Palæarct., Nearct.] 1 „
Cyprinidæ [Palæarct., India, North America]--
Cyprinina [Palæarct., India, N. America--
Labeo [India] 6 „
Barynotus [India] 2 „
_Abrostomus_ 2 „
Discognathus lamta[24] [India] 1 „
Barbus [Palæarct., India] 35 „
Rasborina [India] 1 „
Danionina [India]--
Barilius [India] 3 „
Abramidina [Palæarct., India, N. America]--
_Pelotrophus_ 2 „
_Kneriidæ_ 2 „
Osteoglossidæ [India, Australia, South America]--
_Heterotis_ 1 „
_Pantodontidæ_ 1 „
Notopteridæ [India] 2 „
------------
255 species.
============
Out of the 39 families or groups of freshwater fishes 15 are
represented in the African region, or three more than in the Indian
region; however of two of them, viz., the _Ophiocephalidæ_ and
_Mastacembelidæ_, a few species only have found their way into
Africa. On the other hand, the number of species is much less, viz.
255, which is only two-fifths of that of the known Indian species. The
small degree of specialisation and localisation is principally due to
the greater uniformity of the physical conditions of this continent,
and to the almost perfect continuity of the great river systems,
which take their origin from the lakes in its centre. This is best
shown by a comparison of the fauna of the Upper Nile with that of the
West African rivers. The number of species known from the Upper Nile
amounts to 56, and of these not less than 25 are absolutely identical
with West African species. There is an uninterrupted continuity of the
fish-fauna from west to the north-east, and the species known to be
common to both extremities may be reasonably assumed to inhabit also
the great reservoirs of water in the centre of the continent. A greater
dissimilarity is noticeable between the west and north-east fauna
on the one hand, and that of the Zambezi on the other; the affinity
between them is merely generic; and all the fishes hitherto collected
in Lake Nyassa have proved to be distinct from those of the Nile, and
even from those of other parts of the system of the Zambezi.
Africa, unlike India, does not possess either alpine ranges or outlying
archipelagoes, the fresh waters of which would swell the number of its
indigenous species; but at a future time, when its fauna is better
known than at present, it is possible that the great difference in the
number of species between this and the Indian regions may be somewhat
lessened.
The most numerously-represented families are the Siluroids, with
61 species; the Cyprinoids, with 52; the Mormyridæ, with 51; the
Characinidæ, with 35; and the Chromides, with 29. There is not,
therefore, that great preponderance of the two first families over the
remaining, which we noticed in the Indian region; in Africa there is a
comparatively greater variety of distinct Freshwater types, imparting
to the study of its fauna an unflagging pleasure such as is scarcely
gained by the study of the other region. With the forms peculiar to it
there are combined those of India as well as South America.
In Tropical Africa there are still remnants of Ganoids: _Protopterus_
(_Lepidosiren_) _annectens_ and _Polypterus bichir_, with the
singularly modified _Calamoichthys_. The two former range from east to
west, and are accompanied by an Osteoglossoid (_Heterotis_) which has
hitherto been found in the Nile and on the West Coast only.
Autochthont and limited to this region are the _Mormyridæ_,
_Pantodontidæ_, and _Kneriidæ_, a singular type, somewhat akin to the
Loaches. Of Siluroid genera the most characteristic are _Synodontis_,
_Rhinoglanis_, and the electric _Malapterurus_; of Characinoids,
_Citharinus_, _Alestes_, _Xenocharax_, _Hydrocyon_, _Distichodon_,
_Ichthyborus_.
The regions with which Africa (like India) has least similarity
are, again, the North American and Antarctic. Its affinity with the
Europe-Asiatic region consists only in having received, like this
latter, a branch of the Cyprinoids, the African Carps and Barbels
resembling, on the whole, more Indian than Europo-Asiatic forms. Its
similarity to Australia is limited to the two regions possessing
Dipnoous and Osteoglossoid types. But its relations to the two other
regions of the equatorial zone are near and of great interest.
1. Africa has, in common with India, the Siluroid group of _Clariina_,
the _Silurina_, and _Bagrina_; and more especially the small but very
natural family of _Notopteridæ_, represented by three species in
India, and by two on the _west coast_ of Africa. It would be hazardous
to state at present in which of the two regions these fishes first
made their appearance, but the discovery of remains of _Notopteridæ_
and _Silurina_ in tertiary deposits of Sumatra points to the Indian
region as their original home. We can have less doubt about the other
fishes common to both regions; they are clearly immigrants into Africa
from the East, and it is a remarkable fact that these immigrants
have penetrated to the most distant limits of Africa in the west as
well as in the south,--viz. the _Labyrinthici_, represented by two
genera closely allied to the Indian _Anabas_; the _Ophiocephalidæ_
and _Mastacembelidæ_, a few species of which have penetrated to the
west coast, singularly enough being absent from the eastern rivers;
the _Ariina_, represented by several species, of which one or two
are identical with Indian, having extended their range along the
intervening coasts to the east coast of Africa. The Cyprinoids also
afford an instance of an Indian species ranging into Africa, viz.
_Discognathus lamta_, which seems to have crossed at the southern
extremity of the Red Sea, as it is found in the reservoirs at Aden and
the hill-streams of the opposite coast-region of Abyssinia.
2. No such direct influx of species and genera has occurred from
South America into Africa. Yet the affinity of their Freshwater
fishes is striking. Two of the most natural families of fishes, the
_Chromides_ and _Characinidæ_, are peculiar, and (with the exception of
_Etroplus_) restricted to them. The African and South American Dipnoi
are closely allied to each other. The _Pimelodina_, so characteristic
of Tropical America, have three representatives in Africa, viz.,
_Pimelodus platychir_, _P. balayi_, and _Auchenoglanis biscutatus_;
the _Doradina_ are another Siluroid group restricted to these two
continents.[25] Yet, with all these points of close resemblance, the
African and South American series are, with the exception of the two
species of Pimelodus, _generically_ distinct; which shows that the
separation of the continents must have been of an old date. On the
other hand, the existence of so many similar forms on both sides of
the Atlantic affords much support to the supposition that at a former
period the distance between the present Atlantic continents was much
less, and that the fishes which have diverged towards the East and
West are descendants of a common stock which had its home in a region
now submerged under some intervening part of that ocean. Be this as
it may, it is evident that the physical conditions of Africa and
South America have remained unchanged for a considerable period, and
are still sufficiently alike to preserve the identity of a number of
peculiar freshwater forms on both sides of the Atlantic. Africa and
South America are, moreover, the only continents which have produced in
Freshwater fishes, though in very different families, one of the most
extraordinary modifications of an organ--the conversion, that is, of
muscle into an apparatus creating electric force.
C. The boundaries of the TROPICAL AMERICAN (_Neotropical_) REGION
have been sufficiently indicated in the definition of the Equatorial
zone. A broad and most irregular band of country, in which the South
and North American forms are mixed, exists in the north; offering
some peculiarities which deserve fuller attention in the subsequent
description of the relations between the South and North American
faunæ. The following Freshwater fishes inhabit this region:--
Dipnoi [Australia, Africa]--
_Lepidosiren paradoxa_ 1 species.
_Polycentridæ_ 3 „
Chromides [Africa]--
_Heros_, _Acara_, _Cichla_, etc. 80 „
(_Lucifuga_ 2 „)
Siluridæ--
_Hypophthalmina_ 5 „
Pimelodina [Africa, 2 species] 70 „
Ariina [Africa, India, Australia, Fuegian] 35 „
Doradina [Africa] 60 „
Hypostomatina [India] 90 „
_Aspredinina_ 9 „
Nematogenyina [Fuegian]-- 2 „
Trichomycterina [Fuegian] 2 „
_Stegophilina_ 3 „
Characinidae [Africa]--
_Erythrinina_ 15 „
_Curimatina_ 40 „
_Anastomatina_ 25 „
Tetragonopterina 80 „
Hydrocyonina 30 „
Crenuchina 1 „
Serrasalmonina 35 „
Cyprinodontidæ--
Carnivoræ [Europe, Asia, N. America,
India, Africa] 30 „
_Limnophagæ_ 31 „
Osteoglossidæ [Africa, India, Australia] 2 „
_Gymnotidæ_ 20 „
Symbranchidæ [India] 1 „
------------
672 species.
============
Out of the 39 families or groups of Freshwater fishes, 9 only are
represented in the Tropical American region. This may be accounted for
by the fact that South America is too much isolated from the other
regions of the Equatorial zone to have received recent additions to
its fauna. On the other hand, the number of species exceeds that of
every other region, even of the Indian, with which, in regard to the
comparative development of families, the Neotropical region shows great
analogy, as will be seen from the following Table:--
INDIAN. NEOTROPICAL.
Siluridæ 200 sp. Siluridæ 276 sp.
Cyprinidæ 330 sp. Characinidæ 226 sp.
Labyrinthici 25 sp. Chromides 80 sp.
Ophiocephalidæ 30 sp. Cyprinodontidæ 60 sp.
Mastacembelidæ 10 sp. Gymnotidæ 20 sp.
In both regions the great number of species is due to the development
of numerous local forms of two families, the _Characinidæ_ taking in
the New World the place of the _Cyprinidæ_ of the Old World. Thereto
are added a few smaller families with a moderately large number of
species, which, however, is only a fraction of that of the leading
families, the remainder of the families being represented by a few
species only. The number of genera within each of the two regions of
the two principal families is also singularly alike; the Indian region
having produced about 45 Siluroid and as many Cyprinoid genera, whilst
the Neotropical region is tenanted by 54 Siluroid and 40 Characinoid
genera. These points of similarity between the two regions cannot
be accidental; they indicate that agreement in their physical and
hydrographical features which in reality exists.
Of Ganoids, we find in Tropical America one species only, _Lepidosiren
paradoxa_, accompanied by two Osteoglossoids (_Osteoglossum
bicirrhosum_ and _Arapaima gigas_).
Autochthont and limited to this region are the _Polycentridæ_, all the
non-African genera of _Chromides_ and _Characinidæ_; of Siluroids, the
_Hypophthalmina_, _Aspredinina_, and _Stegophilina_, and the majority
of _Pimelodina_, _Hypostomatina_, and _Doradina_; the herbivorous
Cyprinodonts or _Limnophagæ_, and numerous insectivorous Cyprinodonts
or _Carnivoræ_; and the _Gymnotidæ_ (Electric eel).
The relations to the other regions are as follows:--
1. The resemblances to the Indian and Tropical Pacific regions partly
date from remote geological epochs, or are partly due to that
similarity of physical conditions to which we have already referred.
We have again to draw attention to the unexplained presence in South
America of a representative of a truly Indian type (not found in
Africa), viz. _Symbranchus marmoratus_. On the other hand, a
direct genetic affinity exists between the Neotropical and African
regions, as has been noticed in the description of the latter, a great
part of their freshwater fauna consisting of descendants from a common
stock.
2. A comparison of the specifically Neotropical with the specifically
North American types shows that no two regions can be more dissimilar.
It is only in the intervening borderland, and in the large West Indian
Islands, that the two faunæ mix with each other. We need not enter into
the details of the physical features of Central America and Mexico--the
broken ground, the variety of climate (produced by different altitudes)
within limited districts, the hot and moist alluvial plains surrounding
the Mexican Gulf, offer a diversity of conditions most favourable to
the intermixture of the types from the north and the south. But yet
the exchange of peculiar forms appears to be only beginning; none have
yet penetrated beyond the debatable ground, and it is evident that the
land-connection between the two continents is of comparatively recent
date: a view which is confirmed by the identity of the marine fishes on
both sides of Central America.
Cuba--and this is the only island in the West Indies which has a
number of freshwater fishes sufficient for the determination of its
zoo-geographical relations--is inhabited by several kinds of a perch
(_Centropomus_), freshwater mullets, Cyprinodonts, one species of
Chromid (an _Acara_), and _Symbranchus marmoratus_. All these fishes
are found in Central America, and as they belong to forms known to
enter brackish water more or less freely, it is evident that they
have crossed from the mainland of South America or from Central
America. But with them there came a remarkable North American type,
_Lepidosteus_. _Lepidosteus viridis_, which is found in the United
States, has penetrated on the mainland to the Pacific coast of
Guatemala, where it is common at the mouth of the rivers and in
brack-water lakes along the coast; it probably crossed into Cuba from
Florida. A perfectly isolated type of fishes inhabits the subterranean
waters of the caves of Cuba (two species of _Lucifuga_). The eyes are
absent or quite rudimentary, as in most other cave animals. Singularly,
it belongs to a family (_Ophidiidæ_), the members of which are strictly
marine; and its nearest ally is a genus, _Brotula_, the species of
which are distributed over the Indo-Pacific Ocean, one only occurring
in the Caribbean Sea. This type must have witnessed all the geological
changes which have taken place since Cuba rose above the surface of the
sea.
A similar mixture of forms of the Tropical and Temperate types of
Freshwater fishes takes place in the south of South America; its
details have not yet been so well studied as in the north; but this
much is evident that, whilst in the East Tropical forms follow the
Plate river far into the Temperate region, in the West the Temperate
Fauna finds still a congenial climate in ranges of the Andes, situated
close to, or even north of, the Tropic.
Like the Indian region, the Tropical American has a peculiar Alpine
Fauna, the Freshwater fishes of which, however, belong to the
Siluroids and Cyprinodonts. The former are small, dwarfed forms
(_Arges_, _Stygogenes_, _Brontes_, _Astroblepus_, _Trichomycterus_,
_Eremophilus_), and have a perfectly naked body, whilst the
representatives in the lowlands of, at least, the first four genera are
mailed. The Alpine Cyprinodonts, on the other hand, (_Orestias_) exceed
the usual small size of the other members of this family, are covered
with thick scales, but have lost their ventral fins. Some of these
Alpine forms, like _Trichomycterus_, follow the range of the Andes far
into the southern temperate region. The majority reach to a height
of 15,000 feet above the level of the sea, and a few are found still
higher.
D. The TROPICAL PACIFIC REGION includes all the islands east of
Wallace’s Line, New Guinea, Australia--with the exception of its
south-eastern portion,--and all the islands of the Tropical Pacific to
the Sandwich group. Comparing the area of this region with that of the
others, we find it to be not only the poorest in point of the number of
its species generally, but also in that of the possession of peculiar
forms, as will appear from the following list:--
Dipnoi [Neotrop., Africa.]
_Ceratodus_ 2 species.
Percidæ [Cosmopol.]--
Lates (calcarifer) [India] 1 „
_Nannoperca_ 1 „
Oligorus [New Zealand] 1 „
Dules [India] 8 „
(_Macquaria_) 1 „
Labyrinthici--
Anabas (scandens) [India] 1 „
Ophiocephalidæ--
Ophiocephalus (striatus) [India] 1 „
Atherinidæ [Brack-water]--
Atherinichthys 2 „
Osteoglossidæ [India, Africa, Neotrop.] 1 „
Siluridæ--
Plotosina [India] 9 „
Ariina [India, Africa, Neotrop.] 7 „
Symbranchidæ--
Monopterus (javanicus) [India] 1 „
-----------
Total 36 species.
The paucity of freshwater fishes is due, in the first place, to the
arid climate and the deficiency of water in the Australian continent,
as well as to the insignificant size of the freshwater courses in the
smaller islands. Still this cannot be the only cause: the large island
of Celebes, which, by its mountainous portions, as well as by its
extensive plains and lowlands, would seem to offer a favourable variety
of conditions for the development of a freshwater Fauna is, as far as
has been ascertained, tenanted by seven Freshwater fishes only, viz. 2
_Arius_, 2 _Plotosus_, 1 _Andbas_, 1 _Ophiocephalus_, 1 _Monopterus_,
all of which are the commonest species of the Indian region. New
Guinea has not yet been explored, but, from the faunæ nearest to this
island, we expect its freshwater fishes will prove to be equally few
in number, and identical with those of Celebes and North Australia; a
supposition confirmed by the few small collections which have reached
Europe. Finding, then, that even those parts of this region, which
are favourable to the development of Freshwater fishes, have not
produced any distinct forms, and that the few species which inhabit
them, are unchanged, or but slightly modified Indian species, we must
conclude that the whole of this area has remained geologically isolated
from the other regions of this zone since the commencement of the
existence of Teleostei; and that, with the exception of _Ceratodus_ and
_Osteoglossum_, the immigration of the other species is of very recent
date.
Fossil remains of _Ceratodus_ have been found in Liassic and Triassic
formations of North America, England, Germany, and India; and it is,
therefore, a type which was widely spread in the Mesozoic epoch.
Although it would be rash to conclude that its occupation of Australia
dates equally far back, for it may have reached that continent long
afterwards; yet it is evident that, as it is one of the most ancient
of the existing types, so it is certainly the first of the Freshwater
fishes which appeared in Australia. _Osteoglossum_, of which no fossil
remains yet have been found, is proved by its distribution to be one
of the oldest Teleosteous types. There must have been a long gap of
time before these ancient types were joined by the other Teleostei.
All of them migrated through the intervening parts of the ocean from
India. Most of the _Plotosina_, some of the _Arii_, _Dules_, and
the _Atherinichthys_, also _Nannoperca_ (allied to _Apogon_), were
among the earliest arrivals, being sufficiently differentiated to
be specifically or even generically (_Cnidoglanis_, _Nannoperca_)
distinguished; but some others, like _Anabas scandens_, _Lates
calcarifer_, _Dules marginatus_, must have reached the Australian
continent quite recently, for they are indistinguishable from Indian
specimens.
In South-western Australia a mingling of the scanty fauna with that of
the southern temperate parts takes place. _Oligorus macquariensis_ (The
Murray Cod), which has a congener on the coast of New Zealand, ascends
high up the Murray river, so that we cannot decide whether this Percoid
should be located in the Tropical or Temperate part of Australia.
Several _Galaxias_ also extend to the confines of Queensland, and will
probably some day be found members of this region.
In the smaller Pacific islands the Freshwater fishes exhibit a
remarkable sameness: two or three species of _Dules_, several Eels, an
Atherine, or some Gobies, Mullets, and other fishes which with equal
readiness exchange fresh for salt water, and which would at once reach
and occupy any streams or freshwater lakes that may be formed on an
island.
The Sandwich Islands are the only group among the smaller islands which
are tenanted by a Siluroid, a species of _Arius_, which is closely
allied to Central American species, and, therefore, probably immigrated
from Tropical America.
II. NORTHERN ZONE.
The boundaries of the Northern Zone coincide in the main with the
northern limit of the Equatorial Zone; but at three different points
they overlap the latter, as has been already indicated. This happens
in, and east of, Syria, where the mixed faunæ of the Jordan and the
rivers of Mesopotamia demand the inclusion of this territory into the
Northern Zone as well as the Equatorial; in the island of Formosa,
where a Salmonoid and several Japanese Cyprinoids flourish; and in
Central America, where a _Lepidosteus_, a Cyprinoid (_Sclerognathus
meridionalis_), and an Amiurus (_A. meridionalis_) represent the North
American fauna in the midst of a host of tropical forms.
A separate _Arctic_ Zone does not exist for Freshwater fishes; ichthyic
life becomes extinct towards the pole as soon as the fresh water
remains frozen throughout the year, or thaws for a few weeks only; and
the few fishes which extend into high latitudes, in which lakes are
open for two or three months in the year, belong to types in no wise
differing from those of the more temperate south. The highest latitude
at which fishes have been obtained is 82° lat. N., whence the late
Arctic Expedition brought back specimens of Charr (_Salmo arcturus_ and
_Salmo naresii_).
The ichthyological features of this zone are well marked: the
Chondrosteous Ganoids or Sturgeons, and the families of _Salmonidæ_
and _Esocidæ_ are limited to, and characteristic of, it; Cyprinoids
flourish with the Salmonoids, both families preponderating in numbers
over the others, whilst the Siluroids are few in number and in variety.
The two regions in which this zone is divided are very closely related
to one another, and their affinity is not unlike that which obtains
between the sub-regions of the Southern Zone. The subjoined list will
show their close agreement with regard to families as well as species.
Several of the latter are common to both, viz.--_Acipenser sturio_,
_A. maculatu_s, _Perca fluviatilis_, _Gastrosteus pungitius_, _Salmo
salar_, _Esox lucius_, _Lota vulgaris_, _Petromyzon marinus_, _P.
fluviatilis_, and _P. branchialis_; and all recent investigations have
resulted in giving additional evidence of the affinity, and not of the
diversity of the two regions.
In Europe and temperate Asia, as well as in North America, mountain
ranges elevated beyond the line of perpetual snow would seem to offer
physical conditions favourable for the development of a distinct
alpine fauna. But this is not the case, because the difference of
climate between the mountain districts and the lowlands is much less in
this zone than in the Equatorial. Consequently the alpine freshwater
fishes do not essentially differ from those of the plains; they are
principally Salmonoids; and in Asia, besides, mountain-barbels and
Loaches. _Salmo orientalis_ was found by Griffith to abound in the
tributaries of the Bamean river at an altitude of about 11,000 feet.
Europo-Asiatic. N. American.
_Acipenseridæ_--
Acipenser 9 species. 12 species.
Scaphirhynchus 2 „ 1 „
Polyodon 1 „ 1 „
_Lepidosteidæ_ 0 „ 3 „
_Amiidæ_ 0 „ 1 „
Percina [Cosmopol.] 10 „ 30 „
Grystina [Australia, New Zealand] 0 „ 2 „
_Centrarchina_ 0 „ 26 „
_Aphredoderidæ_ 0 „ 1 „
Cottidæ [partly marine]--
_Cottus_ 3 „ 8 „
_Ptyonotus_ 0 „ 1 „
_Gastrosteidæ_ 5 „ 5 „
_Comephoridæ_ 1 „ 0 „
Gadidæ [marine]--
_Lota_ 1 „ 1 „
Siluridæ--
Silurina [India, Africa] 5 „ 0 „
Bagrina 2 „ 0 „
_Amiurina_ 1 „ 17 „
_Salmonidæ_ 90 „ 45 „
_Percopsidæ_ 0 „ 1 „
_Esocidæ_ 1 „ 7 „
_Umbridæ_ 1 „ 1 „
Cyprinodontidæ Carnivoræ [India,
Africa, Neotrop.] 9 „ 30 „
_Heteropygii_ 0 „ 2 „
Cyprinidæ--
_Catostomina_ 1 „ 25 „
Cyprinina [India, Africa] 80 „ 30 ”
_Leuciscina_ 60 „ 70 „
_Rhodeina_ 10 „ 0 „
Abramidina [India, Africa] 44 „ 10 ”
Cobitidina [India] 20 „ 0 ”
_Hyodontidæ_ 0 „ 1 „
Petromyzontidæ [Southern Zone] 4 „ 8 ”
-----------------------------
360 species. 339 species.
=============================
A. THE EUROPO-ASIATIC (PALÆARCTIC) REGION.--Its western and
southern boundaries coincide with those of the Northern Zone, so that
only those which divide it from North America have to be indicated.
Behring’s Strait and the Kamtschatka Sea have been conventionally
taken as the boundary, but this is shown to be artificial by the fact
that the animals of both coasts, as far as they are known at present,
are not sufficiently distinct to be referred to two distinct regions.
As to the freshwater fishes those of North-western America and of
Kamtschatka are but imperfectly known, but there can be little doubt
that the same agreement exists between them as is the case with other
classes of animals. The Japanese islands exhibit a decided Palæarctic
fish-fauna, which includes Barbus and Cobitioids, forms strange to the
North American fauna. A slight influx of tropical forms is perceived in
the south of Japan, where two Bagrina (_Pseudobagrus aurantiacus_
and _Liocassis longirostris_) have established themselves for a
considerable period, for both are peculiar to the island, and have not
been found elsewhere.
In the east, as well as in the west, the distinction between the
Europo-Asiatic and North American regions disappears almost entirely
the farther we advance towards the north. Of four species of the genus
Salmo known from Iceland, one (_S. salar_) is common to both regions,
two are European (_S. fario_ and _S. alpinus_), and one is a peculiarly
Icelandic race (_S. nivalis_). As far as we know the Salmonoids of
Greenland and Baffin’s Land they are all most closely allied to
European species, though they may be distinguished as local races.
Finally, as we have seen above, the Europo-Asiatic fauna mingles with
African and Indian forms in Syria, Persia, and Afghanistan. _Capoëta_,
a Cyprinoid genus, is characteristic of this district, and well
represented in the Jordan and rivers of Mesopotamia.
Assuming that the distribution of Cyprinoids has taken its origin from
the alpine tract of country dividing the Indian and Palæarctic regions,
we find that this type has found in the temperate region as equally
favourable conditions for its development as in the tropical. Out of
the 360 species known to exist in the Palæarctic regions, no less than
215 are Cyprinoids. In the countries and on the plateaus immediately
joining the Himalayan ranges those mountain forms which we mentioned
as peculiar to the Indian Alps abound and extend for a considerable
distance towards the west and east, mixed with other _Cyprinina_
and _Cobitidina_. The representatives of these two groups are more
numerous in Central and Eastern Asia than in Europe and the northern
parts of Asia, where the _Leuciscina_ predominate. _Abramidina_ or
Breams are more numerous in the south and east of Asia, but they
spread to the extreme north-western and northern limits, to which the
Cyprinoid type reaches. The _Rhodeina_ are a small family especially
characteristic of the East, but with one or two off-shoots in Central
Europe. Very significant is the appearance in China of a species of the
_Catostomina_, a group otherwise limited to North America.
The Cyprinoids, in their dispersal from the south northwards, are
met from the opposite direction by the Salmonoids. These fishes are,
without doubt, one of the youngest families of _Teleostei_, for they
did not appear before the Pliocene era; they flourished at any rate
during the glacial period, and, as is testified by the remnants which
we find in isolated elevated positions, like the Trout of the Atlas,
of the mountains of Asia-Minor, and of the Hindu Kush, they spread to
the extreme south of this region. At the present day they are most
numerously represented in its northern temperate parts; towards the
south they become scarcer, but increase again in numbers and species,
wherever a great elevation offers them the snow-fed waters which they
affect. In the rivers of the Mediterranean Salmonoids are by no means
scarce, but they prefer the upper courses of those rivers, and do not
migrate to the sea.
The Pike, Umbra, several species of Perch and Stickleback, are also
clearly autochthont species of this region. Others belong to marine
types, and seem to have been retained in fresh water at various epochs:
thus the freshwater Cottus (Miller’s Thumb); _Cottus quadricornis_,
which inhabits lakes of Scandinavia, whilst other individuals of the
same species are strictly marine; the Burbot (_Lota vulgaris_); and the
singular _Comephorus_, a dwarfed and much-changed Gadoid which inhabits
the greatest depths of Lake Baikal.
Remnants of the Palæichthyic fauna are the _Sturgeons_ and _Lampreys_.
The former inhabit in abundance the great rivers of Eastern Europe and
Asia, periodically ascending them from the sea; their southernmost
limits are the Yangtse-kiang in the east, and rivers flowing into the
Adriatic, Black and Caspian Seas, and Lake Aral, towards the centre of
this region. None are known to have gone beyond the boundaries of the
Northern Zone. If the Lampreys are justly reckoned among Freshwater
fishes, their distribution is unique and exceptional. In the Palæarctic
region some of the species descend periodically to the sea, whilst
others remain stationary in the rivers; the same has been observed
in the Lampreys of North America. They are entirely absent in the
Equatorial Zone, but reappear in the Temperate Zone of the Southern
Hemisphere. Many points of the organisation of the Cyclostomes indicate
that they are a type of great antiquity.
The remaining Palæarctic fishes are clearly immigrants from
neighbouring regions: thus _Silurus_, _Macrones_, and _Pseudobagrus_
from the Indian region; _Amiurus_ (and, as mentioned above,
_Catostomus_) from North America. The Cyprinodonts are restricted to
the southern and warmer parts; all belong to the carnivorous division.
The facility with which these fishes accommodate themselves to a
sojourn in fresh, brackish, or salt water, and even in thermal springs,
renders their general distribution easily comprehensible, but it is
impossible to decide to which region they originally belonged; their
remains in tertiary deposits round the Mediterranean are not rare.
* * * * *
_B_. The boundaries of the NORTH AMERICAN or NEARCTIC REGION have
been sufficiently indicated. The main features and the distribution
of this fauna are identical with those of the preceding region. The
proportion of Cyprinoid species to the total number of North-American
fishes (135:339) appears to be considerably less than in the Palæarctic
region, but we cannot admit that these figures approach the truth,
as the Cyprinoids of North America have been much less studied than
those of Europe; of many scarcely more than the name is known. This
also applies in a great measure to the Salmonoids, of which only half
as many as are found in the Palæarctic region have been sufficiently
described to be worthy of consideration. North America will, without
doubt, in the end show as many distinct races as Europe and Asia.
Cyprinoids, belonging to genera living as well as extinct, existed
in North America in the tertiary period. At present, _Cyprinina_,
_Leuciscina_, and _Abramidina_ are well represented, but there
is no representative of the Old World genus _Barbus_, or of the
_Cobitidina_[26]; _Rhodeina_ are also absent. On the other hand, a
well-marked Cyprinoid type is developed--the _Catostomina_, of which
one species has, as it were, returned into Asia. Very characteristic is
the group of _Centrarchina_, allied to the Perch, of which there are
some thirty species; two _Grystina_. Of the Sticklebacks there are as
many species as in Europe, and of Pike not less than seven species have
been distinguished. _Umbra_ appears to be as local as in Europe. Some
very remarkable forms, types of distinct families, though represented
by one or two species only, complete the number of North American
autochthont fishes--viz., _Aphredoderus_, _Percopsis_, _Hyodon_, and
the _Heteropygii_ (_Amblyopsis_ and _Chologaster_). The last are
allied to the Cyprinodonts, differing from them in some points of the
structure of their intestines. The two genera are extremely similar,
but _Chologaster_, which is found in ditches of the rice-fields of
South Carolina, is provided with eyes, and lacks the ventral fins.
_Amblyopsis_ is the celebrated Blind Fish of the Mammoth Cave of
Kentucky: colourless, eyeless, with rudimentary ventral fins, which may
be occasionally entirely absent.
A peculiar feature of the North American Fish Fauna is that it has
retained, besides the Sturgeons and Lampreys, representatives of two
Ganoid families, _Lepidosteus_ and _Amia_. Both these genera existed
in tertiary times: the former occurs in tertiary deposits of Europe as
well as North America, whilst fossil remains of _Amia_ have been found
in the Western Hemisphere only.
It is difficult to account for the presence of the _Amiurina_ in North
America. They form a well-marked division of the _Bagrina_, which
are well represented in Africa and the East Indies, but absent in
South America; it is evident, therefore, they should not be regarded
as immigrants from the south, as is the case with the Palæarctic
Siluroids. Nor, again, has the connection between South and North
America been established sufficiently long to admit of the supposition
that these Siluroids could have spread in the interval from the south
to the northern parts of the continent, for some of the species are
found as far north as Pine Islands Lake (54° lat. N.)[27]
III. SOUTHERN ZONE.
The boundaries of this zone have been indicated in the description of
the Equatorial Zone; they overlap the southern boundaries of the latter
in South Australia and South America, but we have not at present the
means of exactly defining the limits to which southern types extend
northwards. This zone includes Tasmania with at least a portion of
South-eastern Australia (_Tasmanian sub-region_), New Zealand and the
Auckland Islands (_New Zealand sub-region_), and Chili, Patagonia,
Terra del Fuego, and the Falkland Islands (_Fuegian sub-region_). No
freshwater fishes are known from Kerguelen’s Land, or from islands
beyond 55° lat. S. The southern extremity of Africa has to be excluded
from this zone so far as Freshwater fishes are concerned.
This zone is, with regard to its extent as well as to the number of
species, the smallest of the three; yet its ichthyological features
are well marked; they consist in the presence of two peculiar
families, each of which is analogous to a northern type, viz. the
_Haplochitonidæ_, which represent the _Salmonidæ_, _Haplochiton_ being
the analogue of _Salmo_, and _Prototroctes_ that of _Coregonus_; and
the _Galaxiidæ_, which are the Pikes of the Southern Hemisphere.
Although geographically widely separate from each other, the Freshwater
fishes of the three divisions are nevertheless so closely allied
that conclusions drawn from this group of animals alone would hardly
justify us in regarding these divisions as sub-regions. One species of
_Galaxias_ (_G. attenuatus_) and the three Lampreys are found in all
three, or at least two, sub-regions.
_Freshwater Fishes of the Southern Zone._
Tasmanian. N. Zealand. Fuegian.
_Percichthys_ ... ... 3
Siluridæ--
_Diplomystax_ ... ... 1
_Nematogenys_ ... ... 1
Trichomycterina [Neotrop.] ... ... 5
_Gadopsidæ_ 1 ... ...
(_Retropinna_ ... 1 ...)
_Haplochitonidæ_ 1 1 1
_Galaxiidæ_ 6 5 4
Petromyzontidæ 3 1 3
-- -- --
11 8 18
But little remains to be added in explanation of this list;
_Percichthys_ is in Chili the autochthont form of the cosmopolitan
group of _Percina_. _Diplomystax_, an Arioid fish of Chili, and
_Nematogenys_ seem to have crossed the Andes from Tropical America
at a comparatively early period, as these genera are not represented
on the eastern side of South America; the _Trichomycterina_ occur on
both sides of the Andes, which they ascend to a considerable height.
_Retropinna_ is a true Salmonoid, allied to, and representing in the
Southern Hemisphere the Northern Smelt, _Osmerus_. In both these
genera a part of the specimens live in the sea, and ascend rivers
periodically to spawn; another part remain in rivers and lakes, where
they propagate, never descending to the sea, this freshwater race
being constantly smaller than their marine brethren. That this small
Teleostean of the Northern Hemisphere should reappear, though in a
generically modified form, in New Zealand, without having spread over
other parts of the Southern Zone, is one of the most remarkable, and
at present inexplicable facts of the geographical distribution of
freshwater fishes.
[Illustration: Fig. 104.--_Haplochiton zebra_, Straits of
Magelhæn.]