The old saying which compares great helplessness to the state of 'a fish out of water,' does not always find a corroborative re-echo in natural history science. As every one knows, different fishes exhibit very varying degrees of tenacity of life when removed from their native element. Thus a herring dies almost immediately on being taken out of water; whilst, on the other hand, the slippery eels will bear removal from their habitat for twenty-four hours or longer; and we have known of Blennies—such as the Shanny (Blennius pholis)—surviving a long journey of some forty-eight hours' duration, when packed amid some damp sea-weed in a box.
But certain fishes are known, not merely to live when taken out of water, but actually of themselves, and as part of their life and habits, to voluntarily leave the water, and disport themselves on land. Of such abnormal fishes, the most famous is the Climbing Perch or Anabas scandens of India, which inhabits the Ganges, and is also found in Asiatic ponds and lakes. These fishes may be seen to leave the water, and to make their way overland, supporting themselves in their jerking gait by means of their strong spiny fins. They appear to migrate from one pool to another in search of 'pastures new,' especially in the dry season, and when the water of their habitats becomes shallow.
The Hindu names applied to these fishes mean 'climbers of trees;' and although statements have been made both by travellers and natives, that the Climbing Perch has been found scaling the stems of trees, these accounts, we fear, must be regarded as of equal value with the native belief that the fishes fall in showers on the land 'from the skies!' Of the power of the fishes to live for five or six days out of water, however, no doubt can be entertained; and their ability to support life under these unwonted conditions, is explained by the fact that certain bones of the head are curiously contorted so as to form a labyrinth, amid the delicate recesses of which a supply of water is retained, for the purpose of keeping the gills moist.
The curious Lepidosirens or Mudfishes, which occur in the Gambia of Africa and the Amazon of South America, exhibit a greater peculiarity of structure which still more completely fits them for living out of water. In the great majority of fishes, a curious sac or bag known as the swimming or air bladder is found. The use of this structure in ordinary fishes is to alter the specific gravity of the animals; and, by the compression or expansion of the air or gases it contains, to enable them to sink or rise in the water at will. In the Mudfishes, however, the air-bladder becomes divided externally into two sacs, whilst internally each division exhibits a cellular structure resembling that seen in the lungs of higher animals. Then also, this elaborate air-bladder communicates with the mouth and throat by a tube, which corresponds to a windpipe. The nostrils of the Mudfishes further open backwards into the mouth; whilst in all other fishes, except in one genus, the nostrils are simple, closed, pocket-like cavities. And it may lastly be noted that the Lepidosirens are provided with true gills, like their ordinary and more commonplace neighbours.
These remarks serve to explain the 'reason why' these fishes can exist for months out of water. Thus, on the approach of the hot season, the Mudfishes leave their watery homes, and wriggle into the soft mud of their rivers. Here they burrow out a kind of nest, coiling head and tail together; and as the mud dries and hardens, the fishes remain in this temporary tomb, breathing throughout the warm season like true land-dwellers, by means of the lung-like air-bladder. When the wet season once more returns, the fishes are aroused from their semi-torpid state by the early rains moistening the surrounding clay; and when the pools and rivers once more attain their wonted depth, the Lepidosirens emerge from their nests, seek the water, breathe by means of their gills, and otherwise lead a true aquatic existence.
With such a combination of the characters of land and water animals, it is little to be wondered at that the true position of the Mudfishes in the zoological scale should have formed a subject for much discussion. They appear, however, to be true fishes, and not amphibians, and they therefore may legally occupy a prominent position among the oddities of their class.
Other curious beings included among the fishes are the so-called Globe-fishes (Diodon, &c.), which derive their name from their power of distending their bodies with air at will; and their bodies being usually provided with spines, they may be judged to present a rather formidable front to any ordinary adversary, in their expanded condition. Then also we have the curious Trigger-fishes (Balistes), so named from the prominent pointed spine in front of the first of the back-fins; this spine firmly holding its erect position until the second spine or fin-ray be depressed, when the first spine is released by mechanism resembling that of the trigger of a gun. The obvious use of such an apparatus is clearly of a defensive kind; and it is remarkable to find a familiar mechanical appliance of man so accurately reproduced in the fish—or rather, vice versâ.
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