_THE MARINE AQUARIUM_
We have already advised our readers to take home their specimens alive
for the purpose of studying their growth and habits. Now, although there
may be some difficulties in the way of keeping marine animals and plants
alive for any considerable time, yet we are inclined to emphasise the
importance of this matter, knowing that the pleasure and instruction
that may be obtained from even a moderately successful attempt to carry
this out will far more than compensate for the amount of trouble
entailed. There are very many marine objects that are exceedingly pretty
and also very instructive, even when studied apart from the life with
which they were associated in the sea. Thus, a well-preserved sea-weed
may retain much of its original beauty of form and colour, the shells of
numerous molluscs and crustaceans exhibit a most interesting variety of
features well worthy of study, and a number of the soft-bodied animals
may be preserved in such a manner as to closely resemble their living
forms. This being the case, we can hardly say anything to discourage
those who gather sea-side objects merely for the purpose of making a
collection of pretty and interesting things to be observed and admired.
Such objects must necessarily afford much pleasure and instruction, and
the time spent in the collection and preparation will certainly cause
the collector to stray to the haunts of the living things, where he is
certain to acquire, though it may be to a great extent unconsciously, a
certain amount of knowledge concerning their habits and mode of life.
Moreover, sea-side collecting is one of the most healthy and
invigorating of all out-door occupations, and for this reason alone
should be encouraged.
Yet it must be observed that he whose sea-side occupation is merely that
of a collector, and whose work at home is simply the mounting and
arranging of the objects obtained, can hardly be considered a
naturalist. Natural history is a living study, and its devotee is one
who delights in observing the growth and development of living things,
watching their habits, and noting their wonderful adaptation to their
environments; and it is to encourage such observation that we so
strongly recommend the young collector to keep his creatures alive as
far as it is possible to do so.
The first thing to settle, then, is the nature of the vessel or vessels
that are to serve the purpose of aquaria for the work of the young
naturalist.
As long as the outdoor work is in progress temporary aquaria will be
very useful as a means by which the objects collected may be sorted and
stored until a final selection is made for the permanent tank. These
temporary aquaria may consist of jars or earthenware pans of any kind,
each containing a few small tufts of weed, preferably attached to pieces
of rock, and a layer of sand or gravel from the beach.
As such temporary aquaria will, as a rule, be within a convenient
distance from the sea-side where the collecting is being done, there
will be, we presume, no great difficulty in the way of obtaining the
frequent changes of water necessary to keep the animals and plants in a
healthy condition, so that we need do no more now than urge the
importance of avoiding overcrowding, and of renewing the water
frequently for the purpose of supplying the air required for the
respiration of the inmates.
When it is desired to isolate small species in such a manner that their
movements may be conveniently observed, glass jars answer well; but
whatever be the form or size of the vessels used, care must be taken to
avoid excess of both light and heat. They should be kept in a cool
place, quite out of the way of direct sunshine, and the glass vessels
used should be provided with a movable casing of brown paper to exclude
all light except that which penetrates from above.
Even temporary aquaria, used merely for the purpose suggested above,
should be carefully watched, for a single day’s neglect will sometimes
result in the loss of several valuable captives. A dead animal should be
removed as soon as it is discovered to avoid the unpleasant results
arising from the putrefaction of its body. The appearance of a scum or
film on the surface of the water should always be regarded with
suspicion. Such a scum should be removed with the aid of absorbent
paper, since it tends to prevent the absorption of oxygen from the air;
and, should the water be tainted in the slightest degree, it should be
changed at once, or, if this is not practicable, air should be driven
into it for some time by means of a syringe with a very fine nozzle.
Such precautions, however, are not so urgently needed when the aquarium
contains crustaceans only, for the majority of these creatures suffer
less than others in the tainted sea water, some even being apparently
quite as comfortable in this as in a supply fresh from the sea.
Sea-weeds exhibiting the slightest tendency to decay must be removed at
once; and, as regards the feeding of the animals, one must be careful to
introduce only as much food as is required for immediate use, so that
there be no excess of dead organic matter left to putrefy. Some of the
marine animals obtained from our shores feed entirely on the minute and
invisible organisms that are always present in the sea water, and others
subsist principally on certain of the weeds. Many, however, of a more
predaceous disposition, capture and devour living prey, while some, and
more especially the crustaceans, are partial to carrion. If, therefore,
the observer desires to study the ways in which the various creatures
secure and devour their food, he should introduce into his aquaria live
marine worms and other small animals, and also small pieces of fish or
flesh.
We will now pass on to the more serious undertaking of the construction
and management of a permanent salt-water aquarium.
The first point to decide is, perhaps, the size of the proposed vessel,
and this will in many cases be determined partly by a consideration of
the space at one’s disposal, and of the apartment it is intended to
occupy. If it is to be placed in a drawing-room or other ordinary
apartment of a dwelling-house, preference should be given to a window
facing the north in order to avoid the direct rays of the sun, but
perhaps no situation is more suitable than a cool conservatory in the
shady part of a garden; and in either case a strong table or other
support should be provided, of a form and size adapted to those of the
aquarium to be constructed.
Various materials may be used in the construction of such an indoor
aquarium, and we shall deal with two or three different types, so that
the reader may make his selection according to his fancy, or to his
mechanical ability, if he intends that it shall be of his own
construction.
We will begin with an aquarium constructed entirely of a mixture of
cement and fine sand, this being the most inexpensive and certainly the
easiest to make; and although it may not be regarded as the most
ornamental--but opinions will differ on this point--yet it has the
decided advantage of being the nearest approach to the natural rock
pool. Though somewhat heavy and cumbersome, even when empty, the amount
of material used in its construction may be varied according to the
taste and convenience of the maker. Further, this form of aquarium is
one that will readily admit of structural alterations at any future
period. It may be deepened at any time; lateral additions or extensions
may be made, or a portion may at any time be shut off for the purpose of
isolating certain of the animals procured.
[Illustration: FIG. 34.--SECTION OF AN AQUARIUM CONSTRUCTED WITH A
MIXTURE OF CEMENT AND SAND]
The first thing to do is to prepare a flat, strong slab of hard wood or
stone, the exact shape and size of the desired artificial pool, and then
cover this, if of wood, with a mixture of fine sand and cement, mixed to
a convenient consistency with water, to the depth of about one inch. The
banks or walls of the pool must then be built up on all sides, and this
is best done by the gradual addition of soft pellets of cement, applied
in such a manner as to produce an irregular surface. Unless the walls of
the aquarium be very thick and massive the cement will soon show a
tendency to fall from its place as the height increases, but this may be
avoided by doing the work in instalments, allowing each portion to set
before further additions are made to the structure.
Since some marine animals like to occupy snug and shady niches in deep
water while others prefer full exposure to the light in shallows,
arrangements should be made for all by varying the depth of the bed, and
providing several little tunnels and caverns. This may be accomplished
either by working the cement itself into suitable form, or by means of
piled stones obtained from the sea beach; and if the latter plan is
adopted, the stones should not be obtained until the aquarium is quite
ready for its living contents; for then a selection of stones and rock
fragments with weeds, anemones, sponges, and other fixed forms of life
attached to them, may be made. The natural appearance of a rock pool is
thus more nearly approached, and in a shorter time than if the sedentary
life were required to develop on an artificial ground.
Objection may be raised to the form of aquarium just described on the
ground that no life within it is visible except when viewed from above.
But is not this also the case with a rock pool on the sea shore? And has
any admirer of nature ever been heard to complain of the beauties of
such a pool because he was unable to look at them through the sides?
Further, it may be urged that the inmates of our aquarium will be living
under more natural conditions than those of the more popular glass-sided
aquaria, _because_ they receive light from above only.
[Illustration: FIG. 35.--CEMENT AQUARIUM WITH A GLASS PLATE IN FRONT]
However, should the reader require a glass front to his cement tank, the
matter is easily accomplished. Three sides are built up as before
described. A sheet of thick glass--plate glass by preference--is then
cut to the size and shape of the remaining space, and this is fixed by
means of cement pressed well against its edges, both inside and outside.
Water should not be put into the tank until it is quite dry; and, if one
side is made of glass, not until the cement surrounding the edge of the
glass has been liberally painted with marine glue, hot pitch, or some
other suitable waterproof material.
If any pipes are required in connection with the water supply of the
aquarium, according to either of the suggestions in a later portion of
this chapter, such pipes may be fixed in their proper places as the
cement sides are being built up.
The next type of aquarium we have to describe is of low cost as far as
the materials are concerned, and one that may be made by any one who has
had a little experience in woodwork; and although the tank itself is of
a simple rectangular form, yet it may be made to look very pretty with a
suitable adjustment of rocks and weeds.
It consists of a rectangular box, the bottom, ends, and back of which
are of hard wood, firmly dovetailed together, and the front of plate
glass let into grooves in the bottom and ends. All the joints and
grooves are caulked with marine glue, but no paint should be used in the
interior.
This form of tank may be vastly improved by the substitution of slabs of
slate for the wood, though, of course, this change entails a much
greater expenditure of both time and cash; but supposing the work to be
well done, the result is everything that could be desired as far as
strength and durability are concerned.
[Illustration: FIG. 36.--AQUARIUM OF WOOD WITH GLASS FRONT]
In either of the rectangular tanks just described glass may be used for
two sides instead of one only; and since this is not a matter of very
great importance, the choice may well be left to the fancy of the one
who constructs it.
Some prefer an aquarium with glass on all sides, and where this is the
case the framework may be made of angle zinc with all the joints
strongly soldered. Such an aquarium may be made in the form of any
regular polygon, for it is no more difficult to construct one of six or
eight sides than of four. It is more difficult, however, to make such an
aquarium perfectly watertight, for the glass, instead of being in
grooves, has to be securely fastened to the metal frame by means of a
cement on one side only, and this cement has to serve the double purpose
of holding the glass and keeping in the water.
Various mixtures have been suggested for this purpose, and among them
the following are perfectly satisfactory:--
1. Litharge 2 parts
Fine sand 2 "
Plaster of Paris 2 "
Powdered resin 1 part
Mix into a very thick paste with boiled linseed oil and a little driers.
2. Red lead 3 parts
Fine sand 3 ”
Powdered resin 1 part
Mix with boiled linseed oil as above.
Both these cements should be applied very liberally, and the aquarium
then allowed to remain quite undisturbed for at least two weeks before
any water is introduced.
[Illustration: FIG. 37.--HEXAGONAL AQUARIUM CONSTRUCTED OF ANGLE ZINC,
WITH GLASS SIDES]
When ready for the water, the bottom of the aquarium should be covered
with a moderately thick layer of fine sand from the sea shore, and
stones then piled in such a manner as to form little tunnels and caves
to serve as hiding-places for those creatures that prefer to be under
cover. As to the selection of stones, we have already suggested that
some may have weeds rooted to them, and that pieces of rock with
anemones, sponges, and other forms of life attached may be chipped off.
Further, on many of our rocky coasts we may find, near low-water mark, a
number of stones covered with a layer of vegetable growth, amongst which
many small animals live, often more or less concealed by their
protective colouring. Some of these stones placed on the bed of the
salt-water aquarium would add greatly to the natural appearance, as well
as give greater variety to the living objects. Shells bearing the
calcareous, snakelike tubes of the common serpula (p. 121), preferably
with the living animals enclosed, will also enhance the general
appearance and interest of the aquarium.
In making preparations previous to the introduction of animal life, due
regard should be paid to the peculiar requirements of the creatures it
is intended to obtain. We have already referred to the advisability of
arranging the bed of the tank in such a manner that the water may vary
considerably in depth, so that both deep and shallow water may be found
by the animals as required, and to the provision of dark holes for
crustaceans and other creatures that shun the light. Very fine sand
should be provided for shrimps, prawns, and other animals that like to
lie on it; and this sand must be deep in places if it is intended to
introduce any of the burrowing molluscs and marine worms.
The water used may be taken from the sea or be artificially prepared.
The former is certainly to be preferred whenever it can be conveniently
obtained, and at the present time few will find much difficulty in
securing a supply, for not only are we favoured with the means of
obtaining any desired quantity by rail at a cheap rate from almost any
seaport, but there are companies in various ports who undertake the
supply of sea water to any part of the kingdom. If the water is to be
conveyed from the coast without the aid of the regular dealers in this
commodity, great care must be taken to see that the barrel or other
receptacle used for the purpose is perfectly clean. Nothing is more
convenient than an ordinary beer or wine barrel, but it should be
previously cleansed by filling it several times with water--not
necessarily sea water--and allowing each refill to remain in it some
time before emptying. This must be repeated as long as the water shows
the slightest colouration after standing for some time in the barrel.
Should any difficulty arise in the way of getting the salt water direct
from the sea, it may be made artificially by dissolving ‘sea salt’ in
the proper proportion of fresh water, or even by purchasing the
different salts contained in the sea separately, and then adding them to
fresh water in proportionate quantities.
The composition of sea water is as follows:--
Water 96·47 per cent.
Sodium chloride 2·70 ”
Magnesium chloride ·36 ”
Magnesium sulphate (Epsom salts) ·23 ”
Calcium sulphate ·14 ”
Potassium chloride ·07 ”
Traces of other substances ·03 ”
100·00
and it will be seen from this table that artificial sea water may be
made by adding about three and a half pounds of sea salt, obtained from
the sea by the simple process of evaporation, to every ninety-six and a
half pounds of fresh water used. In making it there may be some
difficulty in determining the weight of the large volume of water
required to fill an aquarium of moderate dimensions, but this will
probably disappear if it be remembered that one gallon of water weighs
just ten pounds, and, therefore, one pint weighs twenty ounces.
If the sea salt cannot be readily obtained, the following mixture may be
made, the different salts being purchased separately:--
Water 96-1/2 lbs.
Sodium chloride (common salt) 43-1/4 ozs.
Magnesium chloride 5-3/4 ”
Epsom salts 3-3/4 ”
Powdered gypsum (calcium sulphate) 2-1/4 ”
Although in this mixture the substances contained in the sea in very
small quantities have been entirely omitted, yet it will answer its
purpose apparently as well as the artificial sea water prepared from the
true sea salt, and may therefore be used whenever neither sea salt nor
the natural sea water is procurable.
Assuming, now, that the aquarium has been filled with sea water, it
remains to introduce the animal and vegetable life for which it is
intended; and here it will be necessary to say something with regard to
the amount of life that may be safely installed, and the main conditions
that determine the proportion in which the animal and vegetable life
should be present in order to insure the greatest success.
Concerning the first of these we must caution the reader against the
common error of overcrowding the aquarium with animals. It must be
remembered that almost all marine animals obtain the oxygen gas required
for purposes of respiration from the air dissolved in the water. Now,
atmospheric air is only very slightly soluble in water, and hence we can
never have an abundant supply in the water of an aquarium at any one
time. If a number of animals be placed in any ordinary indoor aquarium,
they very soon use up the dissolved oxygen; and, if no means have been
taken to replace the loss, the animals die, and their dead bodies soon
begin to putrefy and saturate the water with the poisonous products of
decomposition.
It is probably well known to the reader that a large proportion of the
oxygen absorbed by the respiratory organs of animals is converted by
combination of carbon into carbonic acid gas within their bodies, and
that this gas is given back into the water where it dissolves, thus
taking the place of the oxygen used in its formation.
If, then, an aquarium of any kind is to be a success, some means must be
taken to keep the water constantly supplied with fresh oxygen quite as
rapidly as it is consumed, and this can be done satisfactorily by the
introduction of a proportionate quantity of suitable living weeds,
providing there is not too much animal life present.
The majority of living plants require carbonic acid gas as a food, and,
under the influence of light, decompose this gas, liberating the oxygen
it contained. This is true of many of our common sea-weeds, and thus it
is possible to establish in a salt-water aquarium such a balance of
animal and vegetable life that the water is maintained in its normal
condition, the carbonic acid gas being absorbed by the plants as fast as
it is excreted by animals, and oxygen supplied by the plants as rapidly
as it is consumed by the animals.
This condition, however, is more difficult to obtain in a salt-water
aquarium than in one containing fresh-water life, partly because,
generally speaking, the sea-weeds do not supply oxygen to the water as
rapidly as do the plants of our ponds and streams, and partly because of
the difficulties attending the successful growth of sea-weeds in
artificial aquaria. Thus it is usually necessary to adopt some means of
mechanically aërating the water; but, for the present, we shall consider
the sea-weeds only, leaving the mechanical methods of aërating the water
for a later portion of this chapter.
In the first place, let us advise the amateur to confine his attention
to the smaller species of weeds that are commonly found in small and
shallow rock pools, for the successful growth of the larger purple and
olive weeds will probably be beyond his power, even though his tank be
one of considerable capacity. The best plan is that we have already
suggested--namely, to chip off small pieces of rock with tufts of weed
attached, and to fix them amongst the rockery of the aquarium, being
careful to place those that grew in shallow water with full exposure to
the light, and those which occupied sheltered and shady places in the
rock pool, respectively, in similar situations in the artificial pool.
For the purposes of aëration we have to rely principally on the bright
green weeds, and preference should be given to any of these that
exhibit, in their natural habitat, a multitude of minute air-bubbles on
the surface of their fronds, for the bubbles consist principally of
oxygen that is being liberated by the plant, and denote that the species
in question are those that are most valuable for maintaining the desired
condition of the water in an aquarium.
Any small sea-weed may be tried at first, but experience will soon show
that some are much more easily kept alive than others. In this
experimental stage, however, a constant watch should be maintained for
the purpose of detecting signs of decay in the marine garden. A plant
should always be removed as soon as it presents any change from the
natural colour, or exhibits the smallest amount of slimy growths on the
surface, for decomposing plants, as well as decaying animals, will soon
convert an aquarium into a vessel of putrid and poisonous water.
It seems almost unnecessary to name a selection of sea-weeds for small
aquaria, seeing that our rock pools produce so many extremely beautiful
species, most of which may be successfully kept alive in a well-managed
tank; but the common Sea Grass (_Enteromorpha compressa_), and the Sea
Lettuce (_Ulva latissima_), also known locally as the Green Laver or
Sloke, are particularly useful for the aëration of the water; while the
Common Coralline (_Corallina officinalis_), the Dulse (_Schizymenia
edulis_), the Peacock’s tail (Padina pavonia), the Irish or Carrageen
Moss (_Chondrus crispus_), _Callithamnion_, _Griffithsia setacea_,
_Plocamium plumosium_, _Rhodymenia palmata_, _Rhodophyllis bifida_, and
_Ceramium rubrum_ are all beautiful plants that ought to give no trouble
to the aquarium-keeper.
It is not advisable to introduce animal life into the aquarium
immediately it is filled, on account of the possibility of the water
being contaminated by contact with the cement that has been used to make
it water-tight. It is safer to allow the first water to stand for a few
weeks, the weeds and all other objects being _in situ_, and the
necessary means employed for perfect aëration during this interval, and
then, immediately before the animals are placed in their new home, to
syphon off the whole of the water, and refill with a fresh supply.
In the selection of animals due regard should be paid to two important
points--first, the danger of overcrowding, and, secondly, the
destructive habits of some of the more predaceous species.
No more than two or three animals should, as a rule, be reckoned for
each gallon of water; and the proportion of animals should be even less
than this when any of them are of considerable size.
As regards the destructive species, these are intended to include both
those that are voracious vegetable feeders and also those whose habit it
is to kill and prey on other creatures.
It must be understood that the weeds are to serve two distinct
purposes:--They are to supply at least some of the oxygen required for
the respiration of the animal inmates, and also to serve as food for
them. Some marine fishes and molluscs feed on the fronds of the weeds,
and among these the common periwinkle may be mentioned as one of the
most voracious. If many such animals are housed in the aquarium, it will
be necessary to replace at intervals those species of weeds that suffer
most from their ravages. The zoospores thrown off by the weeds,
particularly in the autumn, are also valuable as food for some of the
animals.
Notwithstanding the destructive character of the periwinkle just
referred to, it has one redeeming feature, for it is certainly useful in
the aquarium as a scavenger, as it greedily devours the low forms of
vegetable life that cover the glass and rocks, thus helping to keep them
clean; and the same is true of the common limpet and other creeping
molluscs. Some of these are even more to be valued on account of their
partiality for _decaying_ vegetable matter, by devouring which they
reduce the amount of the products of decomposition passing into the
water.
Other details concerning the selection of animal and vegetable life for
the indoor aquarium must be left to the discretion and experience of the
keeper, for it is impossible by written instructions and advice to cover
all the various sources of loss and trouble that may from time to time
arise. If, however, the general hints for the management of the marine
aquarium here given be faithfully followed, there ought to be no further
losses than must accrue from the injudicious selection of animal
species, and these will decrease as experience has been acquired
respecting the habits of the creatures introduced.
We must now pass on to matters pertaining to the maintenance of the
healthy condition of an aquarium which, we will suppose, has been
established with due regard to scientific principles. Under this head we
shall consider, (1) the aëration of the water, (2) the repair of loss
due to evaporation, and (3) the regulation of light and temperature.
It has already been shown that the marine aquarium can hardly be
maintained in a satisfactory condition as regards its air supply by
leaving the aëration of the water entirely to the action of plant life;
and herein this form of aquarium differs from that employed for the
animal and vegetable life derived from ponds and streams. Fresh-water
weeds develop and multiply with such rapidity, and are such ready
generators of oxygen gas that it is a very easy matter to establish a
fresh-water aquarium that will remain in good condition for years with
but little attention; it is therefore important that we should point out
the difference in treatment necessary to those of our readers who are
already acquainted with the comparative ease with which the fresh-water
aquarium may be kept in good order, lest they expect the same
self-aërating condition in the marine tank.
It is never a good plan to leave the renovation of the water of the
aquarium until there are visible signs within that something is going
wrong. It is true that an unsatisfactory condition of the water,
revealed by a slight taint in the odour, or a general turbidity, or the
formation of a slight scum on the surface, may sometimes be rectified by
the prompt application of some method of artificial aëration, but the
aim of the aquarium-keeper should be not the rectification of
unsatisfactory conditions, but the establishment of such a method of
aëration that the unsatisfactory condition becomes an impossibility. We
do not wish to discourage anyone who has the slightest desire to start a
marine aquarium. Our aim is to point out any difficulties that lie in
the way in order that the aquarium may be a success; and thus, having
stated that the difficulties attending it are somewhat greater than
those connected with the management of a fresh-water aquarium, we should
like to add that these practically disappear when one is prepared to
devote a short time at regular intervals in order to see that the
process of aëration is properly carried out.
Some recommend the occasional injection of air by a syringe as one means
of aërating the water; but, although this may be all very well as a
_temporary_ purifier of the slightly tainted aquarium, it is hardly
suitable as a means of maintaining a good, healthy condition. It must be
remembered that oxygen gas--the gas of the atmosphere so essential to
animal life--is only very slightly soluble in water. By this we mean not
only that water dissolves oxygen very slowly, but also that it can never
hold a large supply of the gas at any one time. This being the case, it
is clear that the use of a syringe for a short time, though it
discharges an enormous total volume of air into the water, will result
in the actual solution of only a small quantity. No method of aëration
is perfect that allows the admission of air for a short time only at
comparatively long intervals; the most perfect system is that in which
air is slowly but _continuously_ passed into solution.
Since air is slightly soluble in water, it is clear that it must be
continuously passing into any body of water that has its surface freely
exposed to it; hence a wide and shallow aquarium is much more likely to
keep in good order than one that is narrower and deeper. But, with
marine aquaria, the simple absorption from the air at the surface is not
in itself sufficient, as a rule, to maintain a healthy condition. Yet it
will be advisable to remember this matter when constructing a tank for
marine life.
One of the prettiest, and certainly one of the most effectual, methods
of supplying air to an aquarium is by means of a small fountain with a
very fine spray. The water need seldom be changed, but the fountain may
be fed by water from the aquarium, and as the fine spray passes through
the air it will absorb oxygen and carry it in solution to the tank.
The accompanying diagram illustrates the manner in which this can be
accomplished. The aquarium (A) is supplied with an outlet (O) about an
inch from the top by means of which the water is prevented from
overflowing, and the outlet pipe leads to a vessel (V) of considerable
capacity which, for the sake of convenience and appearance, may be
concealed beneath the table on which the aquarium stands. Some feet
above the level of the aquarium is another vessel (C), supported on a
shelf, having about the same capacity as V, and supplied with a small
compo pipe that passes down into the aquarium, and then, hidden as much
as possible by the rockery, terminates in a very fine jet just above the
level of the water in the centre. The upper vessel should also be
provided at the top with a loose covering of muslin to serve as a
strainer, and this should be replaced at intervals as it becomes clogged
with sedimentary matter.
In order that this arrangement may give perfect satisfaction the two
vessels (C and V) must each be of at least half the capacity of the
aquarium itself, and the total quantity of salt water sufficient to fill
the aquarium together with one of them. It should also be remembered
that since the pressure of water depends not on its quantity, but on its
height measured perpendicularly, it follows that the height to which the
fountain will play is determined by the height of the vessel C above the
level of the jet.
[Illustration: FIG. 38.--METHOD OF AËRATING THE WATER OF AN AQUARIUM
A, aquarium with fountain; C, cistern to supply the fountain;
O, pipe for overflow; V, vessel for overflow]
Let us now suppose that the aquarium and the upper vessel have both been
filled with sea water. The fine jet from the pipe plays into the air and
returns with a supply of oxygen to the aquarium, while the excess above
the level of O passes into the concealed vessel below the table. If the
two vessels are as large as we recommend, and the jet a very fine one,
the fountain may continue to play for hours before C is empty, the
animals of the tank being favoured all this time with a continuous
supply of air. And when the supply from above is exhausted, the contents
of the bottom vessel are transferred to the top one, and at the same
time so effectually strained by the layer of muslin that no sedimentary
matter passes down to choke the fine jet of the fountain. One great
advantage this method possesses is that the living creatures derive the
benefit of a much larger quantity of water than the aquarium alone could
contain; and thus, apart from the aërating effects of the fountain, the
result is the same as if a much larger tank were employed.
In our next illustration (fig. 39) we give a modified arrangement based
on the same principle which may commend itself by preference to some of
our readers. Here the supply pipe to the fountain passes through a hole
in the bottom of the aquarium instead of into the top, and the outlet
pipe is bent downward within so as to form a syphon.
Those who are acquainted with the principle of the syphon will
understand at once the working of such an arrangement as this. Let us
suppose the vessel _c_ to be full of water, and the fountain started,
while the water in the aquarium stands no higher than the level _l_. The
water slowly rises until the level _h_ of the bend of the outlet tube
has been reached, and during the whole of this time no water escapes
through the exit. As soon, however, as the latter level has been
attained, the water flows away into the lower vessel, into which it
continues to run until the lower level is reached, and then the outflow
ceases, not to commence again until the fountain causes the water to
rise to the upper level.
From what has been said the reader will see that the total quantity of
water required in this instance need not exceed the capacity of the
aquarium; also that each of the vessels connected with water supply and
waste should have a capacity equivalent to the volume of water contained
in the aquarium between the two levels _h_ and _l_.
The alternate rising and falling of the water produced in the manner
just described represents in miniature the flow and ebb of the tides,
but perhaps this is in itself of no great advantage in the aquarium
except from the fact that it allows those creatures that prefer to be
occasionally out of the water for a time a better opportunity of
indulging in such a habit. And further, with regard to both the
arrangements for aëration above described, it should be noted that
earthenware vessels are much to be preferred to those made of metal for
the holding of sea water, since the dissolved salts corrode metallic
substances rather rapidly, and often produce, by their chemical action,
soluble products that render the water more or less poisonous.
[Illustration: FIG. 39.--AQUARIUM FITTED WITH APPARATUS FOR PERIODIC
OUTFLOW]
Other methods of aërating the water of aquaria are practised, but these,
as a rule, are only practicable in the case of the large tanks of public
aquaria and biological laboratories, as the mechanical appliances
necessary to carry them out successfully are beyond the means of an
ordinary amateur.
In such large tanks as those referred to it is common to force a fine
jet of air into the water by machinery. Sometimes this air is driven
downward from a jet just below the surface, and with such force that a
multitude of minute bubbles penetrate to a considerable depth before
they commence to rise, but in others the air is made to enter at the
bottom and must therefore pass right through the water.
Of course the amateur aquarium-keeper may carry out this method of
aëration with every hope of success providing he has some self-acting
apparatus for the purpose, or can depend on being able himself to attend
to a non-automatic arrangement at fairly regular intervals, always
remembering that a single day’s neglect, especially in the case of a
small tank with a proportionately large amount of animal life, may lead
to a loss of valuable specimens.
We have already mentioned the use of a syringe as a means by which an
aquarium may be temporarily restored to a satisfactory condition
providing it has not been neglected too long, and some recommend forcing
air, or, still better, pure oxygen gas, from an india-rubber bag into
the water. We have used, for the same purpose, a stream of oxygen from a
steel cylinder of the compressed gas with very satisfactory results; and
since oxygen may be now obtained, ready compressed, at a very low
price--about twopence a cubic foot--there is much to be said in favour
of this method as an auxiliary in the hands of the owner of a small
tank, though we hardly recommend it as a prime means of aëration to take
the place of the fountain.
In any case, where a stream of air or oxygen is employed, an exceedingly
fine jet should be used, in order that the expelled gas may take the
form of a stream of minute bubbles; for, as previously stated, the water
can absorb the gas only very slowly, so that there must necessarily be a
considerable waste when the gas issues rapidly. Further, the smaller the
bubbles passing through the water, the greater is the total surface of
gas in contact with the liquid, the volume of the supply being the same,
and hence the more effectually will the solution of the gas proceed.
Again, another advantage of the fine stream of minute bubbles lies in
the fact that the smaller these bubbles are the more slowly they rise to
the surface of the water, and thus the longer is the time in which the
gas may be absorbed during its ascent.
A fine jet, well suited to the purpose here defined, may be made very
easily by holding the middle of a piece of glass tubing in a gas flame
until it is _very_ soft, and then, immediately on removing it, pulling
it out rather quickly. A slight cut made with a small triangular file
will then enable the operator to sever the tube at any desired point.
Yet another method of maintaining the air supply of aquaria is adopted
in the case of some of the large tanks of public aquaria and biological
laboratories situated close to the sea, and this consists in renewing
the water at every high tide by means of pumps.
It must not be supposed that an indoor aquarium, even when well
established, and supplied with the best possible system of aëration,
requires no further care and attention. In the first place there is a
continual loss of water by evaporation, especially in warm and dry
weather, and this must be rectified occasionally. Now, when water
containing salts in solution evaporates, the water passing away into the
air is perfectly free from the saline matter, and thus the percentage of
salt in the residue becomes higher than before. It is evident,
therefore, that the loss by evaporation in a marine aquarium must be
replaced by the addition of _fresh_ water, which should either be
distilled, or from the domestic supply, providing it is soft and
moderately free from dissolved material.
But the question may be asked, ‘Do not the marine animals and plants
utilise a certain amount of the saline matter contained in the salt
water?’ The answer to this is certainly in the affirmative, for all
sea-weeds require and abstract small proportions of certain salts, the
nature of which varies considerably in the case of different species;
and, further, all the shelled crustaceans and molluscs require the salts
of lime for the development of their external coverings, and fishes for
the growth of their bony skeletons. Hence the above suggestion as to the
replenishment of loss by evaporation with pure water is not perfectly
satisfactory. It will answer quite satisfactorily, however, providing
the sea water is _occasionally_ changed for an entirely new supply.
Again, since carbonate of lime is removed from sea water more than any
other salt, being such an essential constituent of both the external and
internal skeletons of so many marine animals, as well as of the
calcareous framework of the coralline weeds, we suggest that the
aquarium may always contain a clean piece of some variety of carbonate
of lime, such as chalk, limestone, or marble, which will slowly dissolve
and replace that which has been absorbed.
Water is rendered denser, and consequently more buoyant, by the presence
of dissolved salts; and, since the density increases with the proportion
of dissolved material, we are enabled to determine the degree of
salinity by finding the density of the solution. We can apply this
principle to the aquarium, as a means of determining whether the water
contains the correct amount of sea salt, also for testing any artificial
salt water that has been prepared for the aquarium.
Probably some of our readers are acquainted with some form of
hydrometer--an instrument used for finding the density of any liquid;
but we will describe a simple substitute that may be of use to the owner
of a marine aquarium, especially if the salt water for the same is
artificially prepared. Melt a little bees-wax, and mix it with fine,
clean sand. Then, remembering that the wax is lighter than water, and
consequently floats, while sand is considerably heavier, and sinks,
adjust the above mixture until a solid ball of it is just heavy enough
to sink _very slowly_ in sea water. Now make two such balls, and then
cover one of them with a light coating of pure wax. We have now two
balls, one of which will float in sea water, and the other sink, and
these may be used at any time to test the density of the water in, or
prepared for, the aquarium. If the water is only a little too salt, both
balls will float; while, if not sufficiently rich in saline matter, both
will sink.
We must conclude this chapter by making a few remarks on the important
matter of the regulation of light and temperature. Direct sunlight
should always be avoided, except for short and occasional intervals, not
only because it is liable to raise the temperature to a higher degree
than is suitable for the inmates of the aquarium, but also because an
excess of light and heat tends to produce a rapid decomposition of
organic matter, and a consequent putrid condition of the water, and this
dangerous state is most likely to occur when both light and temperature
are high at the same time.
The water should always be cold; and as it is not always easy to
estimate the temperature, even approximately, by the sensation produced
on immersing the fingers, it is a good plan to have a small thermometer
always at hand, or placed permanently in the aquarium. In the summer
time the water should be kept down to fifty-five degrees or lower, and
in winter should never be allowed to cool much below forty. There may be
some difficulty in maintaining a temperature sufficiently low in summer,
but a small piece of ice thrown in occasionally to replace the loss due
to evaporation, especially on very hot days, will help to keep it down.