SALMOPERCÆ AND OTHER TRANSITIONAL
GROUPS
=SUBORDER Salmopercæ, the Trout-perches: Percopsidæ.=—More ancient than
the _Hemibranchii_, and still more distinctly in the line of transition
from soft-rayed to spiny-rayed fishes, is the small suborder of
_Salmopercæ_. This is characterized by the presence of the adipose fin
of the salmon, in connection with the mouth, scales, and fin-spines of a
perch. The premaxillary forms the entire edge of the upper jaw, the
maxillary being without teeth. The air-bladder retains a rudimentary
duct. The bones of the head are full of mucous cavities, as in the
European perch called _Gymnocephalus_ and _Acerina_. There are two
spines in the dorsal and one or two in the anal, while the abdominal
ventrals have each a spine and eight rays. Two species only are known
among living fishes, these emphasizing more perfectly than any other
known forms the close relation really existing between spinous and
soft-rayed forms. The single family of _Percopsidæ_ would seem to find
its place in Cretaceous rocks rather than in the waters of to-day.
[Illustration:
FIG. 191.—Sand-roller, _Pecropsis guttatus_ Agassiz. Okoboji Lake, Ia.
]
_Percopsis guttata_, the trout-perch or sand-roller of the Great Lakes,
is a pale translucent fish with dark spots, reaching a length of six
inches. It abounds in the Great Lakes and their tributaries and is
occasionally found in the Delaware, Ohio, Kansas, and other rivers and
northwestward as far as Medicine Hat on the Saskatchewan. It is easily
taken with a hook from the piers at Chicago.
[Illustration:
FIG. 192.—Oregon Trout-perch, _Columbia transmontana_ Eigenmann.
Umatilla River, Oregon.
]
_Columbia transmontana_ is another little fish of similar type, but
rougher and more distinctly perch-like. It is found in sandy or weedy
lagoons throughout the lower basin of the Columbia, where it was first
noticed by Dr. Eigenmann in 1892. From the point of view of structure
and classification, this left-over form is one of the most remarkable of
American fishes.
[Illustration:
FIG. 193.—_Erismatopterus endlicheri_ Cope. Green River Eocene. (After
Cope.)
]
=Erismatopteridæ.=—Here should perhaps be placed the family of
_Erismatopteridæ_, represented by _Erismatopterus levatus_ and other
species of the Green River Eocene shales. In _Erismatopterus_ the short
dorsal has two or three spines, there are two or three spines in the
anal, and the abdominal ventrals are opposite the dorsal. Allied to
_Erismatopterus_ is _Amphiplaga_ of the same deposits.
We cannot, however, feel sure that these extinct fragments, however well
preserved, belonged to fishes having an adipose fin. Among spiny-rayed
fishes the _Percopsidæ_ alone retain this character, and the real
affinities of _Erismatopterus_ may be with _Aphredoderidæ_ and other
percoid forms.
The relations of the extinct family of _Asineopidæ_ are also still
uncertain. This group comprises fresh-water fishes said to be allied to
the _Aphredoderidæ_, but with the pelvic bones not forked. _Asineops
pauciradiata_, _squamifrons_ and _viridensis_ are described from the
Green River shales. With _Erismatopterus_ all these fishes may belong to
the suborder of _Salmopercæ_, but, as above stated, the possession of
the adipose fin, the most characteristic trait of the _Salmopercæ_,
cannot be verified in the fossil remains.
[Illustration:
FIG. 194.—Shoulder-girdle of the Opah, _Lampris guttatus_ (Brünnich),
showing the enlarged infraclavicle. (After Boulenger.)
]
=Suborder Selenichthyes, the Opahs: Lamprididæ.=—We may bring together
as constituting another suborder certain forms of uncertain
relationship, but which seem to be transitional between deep-bodied
extinct Ganoids and the forms allied to _Platax_, _Zeus_, and
_Antigonia_. The name of _Selenichthyes_ (σηλήνη, moon; ἰχθύς, fish) is
suggested by Boulenger for the group of opahs, or moonfishes. These are
characterized by the highly compressed body, the great development of a
large hypocoracoid, and especially by the structure of the ventral fins,
which are composed of about fifteen rays instead of the one spine and
five rays characteristic of the specialized perch-like fishes. The
living forms of this type are further characterized by the partial or
total absence of the spinous dorsal, by the small oblique mouth, and the
prominence of the ventral curve of the body. A thorough study of the
osteology of these forms living and fossil will be necessary before the
group can be properly defined. The large bone above mentioned was at
first considered by Boulenger as the interclavicle or infraclavicle, the
hypocoracoid being regarded by him as displaced, lying with the
actinosts. But it is certain, from the studies of Mr. Starks, that this
bone is the real hypocoracoid, which in this case is simply exaggerated
in size, but placed as in ordinary fishes.
The single living family, _Lamprididæ_, contains but one species,
_Lampris guttatus_, known as opah, moonfish, mariposa, cravo, Jerusalem
haddock, or San Pedro fish. This species reaches a length of six feet
and a weight of 500 to 600 pounds. Fig. 199 (Vol. I) is taken from a
photograph of an example weighing 317½ pounds taken near Honolulu by Mr.
E. L. Berndt. The body is almost as deep as long, plump and smooth,
without scales or bony plates. The vertebræ are forty-five in number,
and the large ventrals contain about fifteen rays. The dorsal is without
spines, the small mouth without teeth. The color is a "rich brocade of
silver and lilac, rosy on the belly, everywhere with round silvery
spots." The head and back have ultramarine tints, the jaws and fins are
vermilion. On a drawing of this fish made at Sable Island in 1856, Mr.
James Farquhar wrote (to Dr. J. Bernard Gilpin): "Just imagine the body,
a beautiful silver interspersed with spots of a lighter color about the
size of sixpence, the eyes very large and brilliant, with a golden ring
around them. You will then have some idea of the splendid appearance of
the fish when fresh. If Caligula had seen them I might have realized a
fortune."
The skeleton of the opah is very firm and heavy. The flesh is of varying
shades of salmon-red, tender, oily, and of a rich, exquisite flavor
scarcely surpassed by any other fish whatsoever.
The opah is a rare fish, swimming slowly near the surface and ranging
very widely in all the warm seas. It was first noticed in Norway by
Gunner, the good bishop of Throndhjem, about 1780. It was soon after
recorded from Elsinore, Torbay, and Madeira, and is occasionally taken
in various places in Europe. It is also recorded from Newfoundland,
Sable Island, Cuba, Monterey, San Pedro Point (near San Francisco),
Santa Catalina, Honolulu, and Japan.
The specimen studied by the writer came ashore at Monterey in an injured
condition, having been worsted in a struggle with some better-armed
fish.
Allied to _Lampris_ is the imposing extinct species known as
_Semiophorus velifer_ from the Eocene of Monte Bolca near Verona, the
type of the extinct family of _Semiophoridæ_. This is a deep compressed
fish, with very high spinous dorsal and very long, many-rayed ventrals.
Other related species are known also from the Eocene. There is no
evidence of any close relation between these fishes with _Caranx_ or
_Platax_, with which Woodward associates _Semiophorus_.
The _Semiophoridæ_ differ from the _Lamprididæ_ chiefly in the
development of the spinous dorsal fin, which is composed of many slender
rays.
=Suborder Zeoidea.=—Not far from the _Selenichthyes_ and the
_Berycoidei_ we may place the singular group of John Dories, or zeoid
fishes. These have the ventral fins thoracic and many-rayed, the dorsal
fin provided with spines, and the post-temporal, as in the
_Chætodontidæ_, fused with the skull. Dr. Boulenger calls attention to
the close relation of these fishes to the flounders, and suggests the
possible derivation of both from a synthetic type, the _Amphistiidæ_,
found in the European Eocene. The _Amphistiidæ_, _Zeidæ_, and flounders
are united by him to form the group or suborder _Zeorhombi_,
characterized by the thoracic ventrals, which have the rays not I, 5 in
number, by the progressive degeneration of the fin-spines and the
progressive twisting of the cranium, bringing the two eyes to the same
side of the head. It is not certain that the flounders are really
derived from Zeus-like fishes, but no other guess as to their origin has
more elements of probability.
[Illustration:
FIG. 195.—_Semiophorus velifer_ Volta. Eocene. (After Agassiz, per
Zittel.)
]
We may, however, regard the _Zeoidea_ on the one hand and the
_Heterosomata_ on the other as distinct suborders. This is certain, that
the flounders are descended from spiny-rayed forms and that they have no
affinities with the codfishes.
[Illustration:
FIG. 196.—_Amphistium paradoxum_ Agassiz. Upper Eocene. (Supposed
ancestor of the flounders). (After Boulenger.)
]
=Amphistiidæ.=—The _Amphistiidæ_, now extinct, are deep-bodied,
compressed fishes, with long, continuous dorsal and anal fins in which a
few of the anterior rays are simple, slender spines scarcely
differentiated from the soft rays. The form of body and the structure of
the fins are essentially as in the flounders, from which they differ
chiefly by the symmetry of the head, the eyes being normally placed.
_Amphistium paradoxum_ is described by Agassiz from the upper Eocene. It
occurs in Italy and France. In its dorsal and anal fins there are about
twenty-two rays, the first three or four undivided. The teeth are minute
or absent and there is a high supraoccipital crest.
=The John Dories: Zeidæ.=—The singular family of _Zeidæ_, or John
Dories, agrees with Chætodonts in the single character of the fusion of
the post-temporal with the skull. The species, however, diverge widely
in other regards, and their ventral fins are essentially those of the
Berycoids. In all the species there are seven to nine soft rays in the
ventral fins, as in the Berycoid fishes. Probably the character of the
fused post-temporal has been independently derived. The anterior
vertebræ in _Zeus_, as in _Chætodon_, are closely crowded together. In
the _Zeidæ_ the spinous dorsal is well developed, the body naked or with
very thin scales, and provided with bony warts at least around the bases
of dorsal and anal fins. The species are mostly of small size, silvery
in color, living in moderate depths in warm seas. The best-known genus
is _Zeus_, which is a group of shore-fishes of the waters of Asia and
Europe. The common John Dory (called in Germany Härings-König, or king
of the herrings), _Zeus faber_, abounds in shallow bays on the coasts of
Europe. It reaches a length of nearly a foot, and is a striking feature
of the markets of southern Europe. The dorsal spines are high, the mouth
large, and on the sides is a black ring, said by some to be the mark of
the thumb of St. Peter, who is reported to have taken a coin from the
mouth of this species. A black spot on several other species is
associated with the same legend.
[Illustration:
FIG. 197.—The John Dory, _Zeus faber_. Linnæus. Devon, England.
]
On the coasts of Japan abounds the Matao, or target-fish (_Zeus
japonicus_), very similar to the European species and like it in form
and color. _Zenopsis nebulosa_ and _Zen itea_ also occur on the coasts
of Japan. The remaining _Zeidæ_ (_Cyttus_, _Zenopsis_, _Zenion_, etc.)
are all rare species occasionally dredged especially in the Australian
region. _Zeus priscus_ is recorded from the Tertiary, and _Cyttoides
glaronensis_ from the upper Eocene of Glavus.
=Grammicolepidæ.=—The _Grammicolepidæ_, represented by a single species,
_Grammicolepis brachiusculus_, rarely taken off the coast of Cuba, is
related to the _Zeidæ_. It has rough, ridged, parchment-like scales
deeper than long. The ventrals are thoracic, with the rays in increased
number, as in _Zeus_ and _Beryx_, with each of which it suggests
affinity.