CHAPTER VIII.
THE FISH AND CRUSTACEANS OF THE AQUARIUM.
A marine Aquarium may be rendered very interesting without the introduction of fish, and as their presence requires that the water should be once each day aerated by means of additional water, introduced by the syringe or by a drip, continuing for some time from another vessel, many may prefer the lovely Sea-Weeds, curious Zoöphytes, and beautiful Molluscs, alone; as, if the balance between the amount of animal and vegetable life be felicitously balanced, and the natural scavengers, in the shape of Periwinkles and other Sea-Snails, for the consumption of decaying vegetable matter, and a few Prawns to perform a similar office for perishing _Infusoriæ_, or any other animal matter, be properly supplied—the tank may remain for a long time undisturbed, the supply of oxygen being ample for the lower classes of animal life alluded to. The beautiful _Actiniæ_, indeed, will exist in apparent health for a considerable time in water in which no vegetable growth has been introduced. Mr. Gosse describes instances in which the water in glass Aquaria, containing Sea-Anemonies, has remained perfectly pure for more than a year.
The addition of fish, however, undoubtedly enlivens the general aspect of an Aquarium very considerably; and many may not grudge the task of daily aerating the water, in order to enjoy the cheerful spectacle of their agreeable and ever-active movements. One or two young Flounders, very small, and the young of other species of flat fish, add much interest to an Aquarium, in consequence of their mode of swimming being so different to that of the class of fishes with whose movements the eye is more familiar.
Among the fish mentioned by the most experienced in the keeping of Sea Aquaria as best suited to that purpose, the first is the pretty little Tansy, _Blennius pholis_, with its bright scarlet eyes, and the many changing hues of its body. This little fellow will live and flourish in a tank with a poorer supply of oxygen than any other fish yet tried.
The fifteen-spined Stickleback, _Gasterosteus spinachia_, does well, and is very cheerful and brisk in his movements. Three or four would be an improvement to any tank.
Young of the gray Mullet, too, do well; for if the supply of oxygen be rather inadequate, they are observed to put their heads partly above the surface of the water, and obtain an artificial supply in that surreptitious manner. The black Goby, _Gobius niger_, has also been tried with success; but his voracious character—devouring without scruple even his own congeners—renders him on the whole not a very desirable tenant; and yet it is a fine sight to see the little warrior turn black when he seizes his prey, his turquois-coloured eyes dilating with fury.
Several other kinds are mentioned, in a previous page, in the list of animals placed by Mr. Gosse in his first experimental Aquarium.
The Pogge, _Aspidophorus cataphractus_, is a singularly formed fish that might be added by way of experiment. The plate-armour in which his body is clothed runs in regular longitudinal lines, showing eight sharp ridges, running from head to tail, that have a singular and unfish-like appearance. In confinement, however, he does not display himself to advantage, generally lying near the bottom of the Aquarium.
The beautiful crimson maculations of the Ancient Wrasse, _Labrus maculatus_, render him a very desirable tenant; but his size—small specimens being eight or nine inches long—causes him to be inconvenient; and, moreover, he is difficult to manage, and would probably require altogether a special treatment. One of the smaller Wrasses, however, _Crenilabrus cornubicus_, is a desirable guest; his minute size, and varying and often gay colours, rendering him very attractive. He is an active and eager searcher for food, but never takes any loosely floating object, only darting at and detaching such atoms as are attached to the different species of Algæ.
The Pipe-Fish, _Syngnathus acus_, is interesting in the tank, and also the two-spotted sucker, _Lepidogaster bimaculatus_, a prettily coloured and curious little fish, which has the faculty of attaching itself to the side of the tank, or any other hard flat surface, by means of two singularly-formed ventral fins, which act like the leather suckers by means of which boys enjoy the sport of lifting heavy stones at the end of a string. The spawn of this fish is like tiny amber beads, and is attached to shells and other substances.
Among the Crustacea fitted for an Aquarium, the common Prawn, _Palæmon serratus_, holds the first rank. In the first place, his cleansing properties, in devouring all decaying animal matter, are most important. But not less interesting are his graceful movements: Now, he steals stealthily over the pebbles or the fronds of the Algæ, with his long, slender, hair-like horns in gentle motion, with all the seeming wariness of a cat (the resemblance being increased by candle-light by the fiery glare of the eye); next, leaving his walking apparatus, or legs, inactive, he uses only the swimming members, which are larger and flatter, and bordered with a compact fringe; agitating these instruments with beautiful regularity, he rises in the water with graceful ease (see Plate VI.), his semi-transparent body, as he rises, giving to his appearance a strange and somewhat apparition-like aspect, which has caused him to be compared to a marine spectre.
The Prawn takes its food with its _second_ feet, two-fingered hands or claws, and carries it to its mouth. The hands of the _first_ pair of legs are only rudimental in appearance, but are precisely fitted to their special purpose. They are his cleansing apparatus; and it is most interesting to watch the operations of his toilet when he uses these fringes as brushes, with which he cleanses his whole person most thoroughly, being almost unmerciful in the amount of severe scrubbing to which he subjects himself.
An allied species, _P. squilla_, is scarcely distinguishable from _P. serratus_; but the handsome scarlet-striped Prawn, _Pardulus annuticornis_, about the size of a Shrimp, is quite distinct, and would make a valuable addition to the collection. The Lobster Prawn, also, _Athanas nilescens_, has likewise been tried.
Some kinds of Crabs may be admitted, but not many; for several are extremely voracious, and would soon clear off all the naked Zoöphytes and most of the Molluscs.
The Climbing Crab, _Eurynome aspera_, is interesting in a tank from his habits. His climbing is as graceful and skilful as that of a monkey, and when he has succeeded in perching himself upon the highest object in the tank, he forms a picturesque object.
Crabs, like Prawns, are sea-scavengers, and the kinds that do not attack living creatures as well as dead are consequently useful in a tank. The great Fiddler Crab, _Portunus puber_, is remarkably handsome. He is clothed, in part, with a velvety brown fur, and the bare places of his shell are of a shining black. His eyes are marked with scarlet, and there are a few touches of bright blue about the head. If introduced, his proceedings should be carefully watched.
There should certainly be a specimen of the Hermit Crab in a Whelk-shell; and the Cleanser Crab, _Portunus depurator_, has been tried, but these active and greedy Sea-Spiders must be closely looked after.
It remains to speak of the Star-Fish tribe, which affords some of the most beautiful and easily managed subjects for the Aquarium.
In the centre of the lower part of Plate VI. are a large and a small specimen of the beautiful scarlet species, _Geniaster equestres_; just above, to the right, the graceful pink _Cribella oculata_; further to the right, _Asteria gibbosa_; and immediately above the _Cribella_, the thin, leathery species, the bird’s foot Sea-Star, _Palmipes membranaceus_. All these species are small, easily managed, and especially suited to the Aquarium; as is also the finely-marked and long-rayed _Ophicoma rosula_, his deep scarlet, with bright black marks, and his slender limbs or rays, rendering him a conspicuous object. These Star-Fish glide round the Aquarium, by the aid of their thousand sucker-like feet, in a very interesting manner.
All the true Star-Fishes, the _Asteriæ_, have the body divided into rays, like a star, and are furnished with sucking feet, or _cirrhi_, which are tubular, and filled with water. The internal structure of these creatures is very intricate and beautiful, and the skeleton of almost any kind offers the appearance of that of some exquisitely symmetrical flower. There are fourteen British species of Star-Fish, the finest being the Sun-Star, _Solaster papposa_, the disk, surrounded with twelve or thirteen rays, varying in colour from scarlet to deep purple, the rays being sometimes of a different colour.
The _Luidia fragilissima_ is also a large kind, sometimes two feet across, which is peculiar to the British shores. It possesses the peculiar faculty of breaking itself into fragments when enraged or captured; and, in a work by the lamented Professor Forbes, there is a very graphic and facetious account of a specimen that escaped him in a very determined way by a suicide of this kind.
Stars of this class, having the power to dislocate their structure, are popularly known as brittle Stars. Some affect to consider this faculty not so very wonderful; but let such suppose for a moment some higher animal—a man, for instance—gifted with a capacity for exploding his trunk and limbs into moderately-sized fragments—into joints, as a butcher would say—at any slight provocation, and then the character of such a power would appear very sufficiently extraordinary. It is possible that the fragments of the disruptured Star-Fish have the power, in each separate fragment, of renewing the absent portions, and that each portion thus becomes a perfect fish, the dissevered portions having been noticed to retain their vitality long after their separation. We know that the little Garden Lizard has the power of dislocating his tail without effort, and leaving it between the thumb and finger, when he is playfully caught by that appendage; and, also, that he has the power of renewing his caudal extremity within a very short period. It is thought, therefore, not impossible, reasoning by analogy, that the Star-Fish may possess powers of a similar kind, of a somewhat more extensive character.
The Amnion Star-Fish, called sometimes Five-fingered (_Asterias rubens_), belongs to the division _Echinodermata_, that is, skinned like the Hedgehog.
The Sea-Egg, Sea-Urchin, or Egg-Urchin, as it is sometimes called, belongs also to the _Echinodermata_, or Hedgehog-skinned class, and form interesting objects in the Aquarium; the flat species exhibiting much more evidently their close affinity to the Star-Fish tribe, than those of the more common spherical form.
To revert to other classes that occur to me as suitable objects for an Aquarium, I may mention the “Red-noses,” as they are graphically termed (_Saxicava rugosa_), a colony of which, peeping out of their holes in the rock, would form a very striking object; and if a piece of their native rock could be detached sufficiently deep not to disturb them in the recesses of their tube-like burrows, their removal “_en bloque_” would not be difficult. When touched, the Red-nose squirts a stream of water at you in defiance, and darts back into his cavern. He is a small bivalve, having his inner or immediate home within two rough brown shells. The double-tubed proboscis with which he is furnished is extended, when in search of food, to the mouth of his cave, in which position the appearance of its ruddy terminus has given to this tribe the characteristic name of “Red-noses.” How he contrives to bore a hole in the solid rock, with any of the soft pulpy members with which he is furnished, appears a mystery. Other Conchifers have, however, similar capabilities, their ingenuity not being confined to rocks, and their industry not being always harmless. Such, for instance, is that of the Teredo, or Ship-worm, a species of which has long proved so inimical to the formation of a Russian fleet in the Black Sea—the late war having, however, proved a far more serious impediment to the development of that portion of the Russian navy.
The Sea-Leaf, formed of twenty thousand or more cradles for young Polypes, is also a curious object. It is the Polyzoön, sometimes called the Hornwrack.
A few of the translucent Medusæ, in a young stage of their existence, might be procured and tried, though their transport would be difficult; and a group of creatures, of the genus _Zoöthamnium_, forming, as they do, an object like a little tree of glass, covered with trumpet-shaped bells, of the same crystalline aspect, each exhibiting its rotating circle of minute cilia in rapid motion within, would form a singular and beautiful complement to the wonders of the Aquarium, if its removal from its native depths, and its location in its new home, could be successfully managed.