CHAPTER XIX.

SUB-AQUATIC NESTS. VERTEBRATES.

Fishes as architects-The STICKLEBACKS and their general habits-The FRESH WATER STICKLEBACKS-A jealous proprietor-Punishment of trespassers-Form and materials of the nest-Use of the nest-Cannibalistic propensitiesThe FIFTEEN-SPINED STICKLEBACK, and its form-Its curious nest-Mr. Couch's description of a nest in a rope's end-Fishes of Guiana-The HASSAR or HARDBACK, and its place in zoology-Nest of the Hassar-Parental watchfulness-Singular position of the nest-Habits of the Hassar.

As a rule, FISHES display but little architectural genius, their anatomical construction debarring them from raising any but the simplest edifice. A fish has but one tool, its mouth, and even this instrument is of very limited capacity. Still, although the nest which a fish can make is necessarily of a slight and rude character, there are some members of that class which construct homes which deserve the name.

The best instances of architecture among the Fishes are those which are produced by the STICKLEBACKS (Gasterosteus), those well-known little beings whose spiny bodies, brilliant colours, and dashing courage make them such favourites with all who study nature. There are several species of British Sticklebacks, but as the fresh-water species all make their nests in a very similar manner, there will be no need of describing each species separately.

These fishes make their nests of the delicate vegetation that is found in fresh water, and will carry materials from some little distance in order to complete the home. They do not, however, range to any great extent, because they would intrude upon the preserve of some other fish, and be ruthlessly driven away.

When the male Stickleback has fixed upon a spot for his nest, he seems to consider a certain area around as his own

especial property, and will not suffer any other fish to intrude within its limits. His boldness is astonishing, for he will dash at a fish of ten times his size, and, by dint of his fierce onset and his bristling spears, drive the enemy away. Even if a stick be placed within the sacred circle, he will dart at it, repeating the assault as often as the stick may trespass upon his domains. Within this limit, therefore, he must seek materials for his nest, as he can hardly move for six inches beyond it without intruding upon the grounds of another fish. This right of property only seems to extend along the banks and a few inches outwards, the centre of the stream or ditch being common property. Along the bank, however, where vegetation is most luxuriant, there is scarcely a foot of space that is not occupied by some Stickleback, and jealously guarded by him.

Although the nests of the Stickleback are plentiful enough, they are not so familiar to the public as might be expected, principally because they are very inconspicuous, and few of the uninitiated would know what they were, even if they were pointed out. Being of such very delicate materials, and but loosely hung together, they will not retain their form when they are removed from the water, but fall together in an undistinguishable mass, like a coil of tangled thread that had been soaked in water for a few weeks.

The materials of which the nest is made are extremely variable, but they are always constructed so as to harmonize with the surrounding objects, and thus to escape ordinary observation. Sometimes it is made of bits of grass which have been blown into the river, sometimes of straws, and sometimes of growing plants. The object of the nest is evident enough, when the habits of the Stickleback are considered. As is the case with many other fish, there are no more determined destroyers of Stickleback eggs than the Sticklebacks themselves, and the nests are evidently constructed for the purpose of affording a resting-place for the eggs until they are hatched. If a few of these nests be removed from the water in a net, and the eggs thrown into the stream, the Sticklebacks rush at them from all sides, and fight for them like boys scrambling for halfpence. The eggs are very small, barely the size of dust-shot, and are yellow when first placed in the nest, but deepen in colour as they approach maturity.

THE FIFTEEN-SPINED STICKLEBACK-THE HASSAR.

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THERE is a well-known marine species of this group, called the FIFTEEN-SPINED STICKLEBACK (Gasterosteus spinachia), a longbodied, long-snouted fish, with a slightly projecting lower jaw, and a row of fifteen short and sharp spines along the back. This creature makes its nest of the smaller algæ, such as the corallines, and the delicate green and purple seaweeds which fringe our coasts.

Sometimes, indeed, it becomes rather eccentric in its architecture, and builds in very curious situations. Mr. Couch, the well-known ichthyologist, mentions a case where a pair of Sticklebacks had made their nest "in the loose end of a rope, from which the separated strands hung out about a yard from the surface, over a depth of four or five fathoms, and to which the materials could only have been brought, of course in the mouth of the fish, from the distance of about thirty feet. They were formed of the usual aggregation of the finer sorts of green and red seaweed, but they were so matted together in the hollow formed by the untwisted strands of the rope, that the mass constituted an oblong ball of nearly the size of the fist, in which had been deposited the scattered assemblage of spawn, and which was bound into shape with a thread of animal substance, which was passed through and through in various directions, while the rope itself formed an outside covering to the whole."

THIS is not the only fish that is known to construct a nest. In the fresh waters of tropical America there is a genus of fish belonging to the Siluridæ, and named Callichthys, from the beauty of the species. The fishes of this genus have four very long barbules hanging from the upper lip and pointing backwards, and are all mailed except part of the belly. Their general colour is green-brown, and they do not reach to any great size, eight inches being their usual length. They are generally very fat, and are much valued by the natives of Guiana, who live so much upon fish. The native name for this fish is HASSAR, and the European residents call it the HARDBACK, in allusion to its coat of shining mail.

To the naturalist, however, the chief point of interest in these fish is the fact that they are in the habit of constructing nests which are quite as well formed as those of the stickleback, and are made of grass-blades, straws, and leaves. These nests are