CHAPTER XIV.. Domesticated and Acclimatised Fishes; Artificial Impregnation

DOMESTICATED AND ACCLIMATISED FISHES; ARTIFICIAL IMPREGNATION OF OVA--TENACITY OF LIFE AND REPRODUCTION OF LOST PARTS--HYBERNATION--USEFUL AND POISONOUS FISHES.

A few fishes only are thoroughly domesticated--that is, bred in captivity, and capable of transportation within certain climatic limits--viz. the Carp, Crucian Carp (European and Chinese varieties), Tench, Orfe or Ide, and the Goramy. The two former have accompanied civilised man almost to every place of the globe where he has effected a permanent settlement.

Attempts to acclimatise particularly useful species in countries in which they were not indigenous have been made from time to time, but were permanently successful in a few instances only; the failures being due partly to the choice of a species which did not yield the profitable return expected, partly to the utter disregard of the difference of the climatic and other physical conditions between the original and new homes of the fish. The first successful attempts of acclimatisation were made with domestic species, viz. the Carp and Gold-fish, which were transferred from Eastern Asia to Europe. Then, in the first third of the present century, the Javanese Goramy was acclimatised in Mauritius and Guiana, but no care seems to have been taken to insure permanent advantages from the successful execution of the experiment. In these cases fully developed individuals were transported to the country in which they were to be acclimatised. The most successful attempt of recent years is the acclimatisation of the Trout and Sea-Trout, and probably also of the Salmon, in Tasmania and New Zealand, and of the Californian Salmon (Salmo quinnat?), in Victoria, by means of artificially-impregnated ova. The ova were transported on ice, in order to retard their development generally, and thus to preserve them from destruction during the passage of the tropical zone.

Artificial impregnation of fish-ova was first practised by J. L. JACOBI, a native of Westphalia, in the years 1757–63, who employed exactly the same method which is followed now; and there is no doubt that this able observer of nature conceived and carried out his idea with the distinct object of advantageously restocking water-courses which had become unproductive, and increasing production by fecundating and preserving all ova, of which a great proportion, in the ordinary course of propagation, would be left unfecundated or accidentally perish. Physiology soon turned to account Jacobi’s discovery, and artificial impregnation has proved to be one of the greatest helps to the student of embryology.

Fishes differ in an extraordinary degree with regard to tenacity of life. Some will bear suspension of respiration--caused by removal from water, or by exposure to cold or heat--for a long time, whilst others succumb at once. Nearly all marine fishes are very sensitive to changes in the temperature of the water, and will not bear transportation from one climate to another. This seems to be much less the case with some freshwater fishes of the temperate zones: the Carp may survive after being frozen in a solid block of ice, and will thrive in the southern parts of the temperate zone. On the other hand, some freshwater fishes are so sensitive to a change in the water that they perish when transplanted from their native river into another apparently offering the same physical conditions (Grayling, Salmo hucho). Some marine fishes may be abruptly transferred from salt into fresh water, like Sticklebacks, some Blennies, and Cottus, etc.; others survive the change when gradually effected, as many migratory fishes; whilst again, others cannot bear the least alteration in the composition of the salt water (all pelagic fishes). On the whole, instances of marine fishes voluntarily entering brackish or fresh water are very numerous, whilst freshwater fishes proper but rarely descend into salt water.

Abstinence from food affects different fishes in a similarly different degree. Marine fishes can endure hunger less than freshwater fishes, at least in the temperate zones, no observations having been made in this respect on tropical fishes. Goldfishes, Carps, Eels, are known to be able to subsist without food for months, without showing a visible decrease of bulk; whilst the Trigloids, Sparoids, and other marine fishes, survive abstinence from food for a few days only. In freshwater fishes the temperature of the water is of great influence on their vital functions generally, and consequently on their appetite,--many cease to feed altogether in the course of the winter; a few, like the Pike, are less inclined to feed during the heat of the summer than when the temperature is lowered.

Captivity is easily borne by most fishes, and the appliances introduced in our modern aquaria have rendered it possible to keep in confinement, and even to induce to propagate, fishes which formerly were considered to be intolerant of captivity.

Wounds affect fishes generally much less than higher Vertebrates. A Greenland Shark continues to feed whilst his head is pierced by a harpoon or by the knife, as long as the nervous centre is not touched; a Sea-perch or a Pike (Fig. 97) will survive the loss of a portion of its tail; a Carp that of half of its snout. However, some fishes are much more sensitive, and perish even from the superficial abrasion caused by the meshes of the net during capture (Mullsn.)

The power of reproduction of lost parts in Teleosteous fishes is limited to the delicate terminations of their fin-rays and the various tegumentary filaments with which some are provided. These filaments are sometimes developed in an extraordinary degree, mimicking the waving fronds of the seaweed in which the fish hides. Both the ends of the fin-rays and the filaments are frequently lost, not only by accident, but merely by wear and tear; and as these organs are essential for the preservation of the fish, their reproduction is necessary.

In Dipnoi, Ceratodus, and Protopterus, the terminal portion of the tail has been found to have been reproduced, but without the notochord.

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Hybernation has been observed in many Cyprinoids and Murænoids of the temperate zones. They do not fall into a condition of complete torpidity, as Reptiles and Mammals, but their vital functions are simply lowered, and they hide in sheltered holes, and cease to go abroad in search of their food. Between the tropics a great number of fishes (especially Siluroids, Labyrinthici, Ophiocephaloids, the Dipnoi), are known to survive long-continued droughts by passing the dry season in a perfectly torpid state, imbedded in the hardened mud. Protopterus, and probably many of the other fishes mentioned, prepare for themselves a cavity large enough to hold them, and coated on the inside with a layer of hardened mucus, which preserves them from complete desiccation. It has been stated that in India fishes may survive in this condition for more than one season, and that ponds known to have been dry for several years, and to the depth of many feet, have swarmed with fishes as soon as the accumulation of water released them from their hardened bed.

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The principal use derived by man from the class of Fishes consists in the abundance of wholesome and nourishing food which they yield. In the Polar regions especially, whole tribes are entirely dependent on this class for subsistence; and in almost all nations fishes form a more or less essential part of food, many being, in a preserved condition, most important articles of trade. The use derived by man from them in other respects is of but secondary importance. Cod-liver oil is prepared from the liver of some of the Gadoids of the Northern Hemisphere, and of Sharks; isinglass from the swim-bladder of Sturgeons, Sciænoids, and Polynemoids; shagreen from the skin of Sharks and Rays.

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The flesh of some fishes is at times, or constantly, poisonous. When eaten, it causes symptoms of more or less intense irritation of the stomach and intestines, inflammation of the mucous membranes, and not rarely death. The fishes, the flesh of which appears always to have poisonous properties, are Clupea thrissa, Clupea venenosa, and some species of Scarus, Tetrodon, and Diodon. There are many others which have occasionally or frequently caused symptoms of poisoning. Poey enumerates not less than seventy-two different kinds from Cuba; and various species of Sphyræna, Balistes, Ostracion, Caranx, Lachnolæmus, Tetragonurus, Thynnus, have been found to be poisonous in all seas between the tropics. All or nearly all these fishes acquire their poisonous properties from their food which consists of poisonous Medusæ, Corals, or decomposing substances. Frequently the fishes are found to be eatable if the head and intestines be removed immediately after capture. In the West Indies it has been ascertained that all the fishes living and feeding on certain coral banks are poisonous. In other fishes the poisonous properties are developed at certain seasons of the year only, especially the season of propagation: as the Barbel, Pike, and Burbot, whose roe causes violent diarrhœas when eaten during the season of spawning.

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Poison-organs are more common in the class of Fishes than was formerly believed, but they seem to have exclusively the function of defence, and are not auxiliary in procuring food, as in venomous Snakes. Such organs are found in the Sting-rays, the tail of which is armed with one or more powerful barbed spines. Although they lack a special organ secreting poison, or a canal in or on the spine by which the venomous fluid is conducted, the symptoms caused by a wound from the spine of a Sting-ray are such as cannot be accounted for merely by the mechanical laceration, the pain being intense, and the subsequent inflammation and swelling of the wounded part terminating not rarely in gangrene. The mucus secreted from the surface of the fish and inoculated by the jagged spine evidently possesses venomous properties. This is also the case in many Scorpænoids, and in the Weaver (Trachinis), in which the dorsal and opercular spines have the same function as the caudal spines of the Sting-rays; however, in the Weavers the spines are deeply grooved, the groove being charged with a fluid mucus. In Synanceia the poison-organ (Fig. 99,) is still more developed: each dorsal spine is in its terminal half provided with a deep groove on each side, at the lower end of which lies a pear-shaped bag containing the milky poison; it is prolonged into a membranous duct, lying in the groove of the spine, and open at its point. The native fishermen, well acquainted with the dangerous nature of these fishes, carefully avoid handling them; but it often happens that persons wading with naked feet in the sea, step upon the fish, which generally lies hidden in the sand. One or more of the erected spines penetrate the skin, and the poison is injected into the wound by the pressure of the foot on the poison-bags. Death has not rarely been the result.

1. Hinder half of the head, with the venom-sac* in situ. a, Lateral line and its branches; b, Gill-opening; c, Ventral fin; d, Base of Pectoral fin; e, Base of dorsal.

2. Operculum with the perforated spine.]

The most perfect poison-organs hitherto discovered in fishes are those of Thalassophryne, a Batrachoid genus of fishes from the coasts of Central America. In these fishes the operculum again and the two dorsal spines are the weapons. The former (Fig. 100, ^2) is very narrow, vertically styliform and very mobile; it is armed behind with a spine, eight lines long, and of the same form as the hollow venom-fang of a snake, being perforated at its base and at its extremity. A sac covering the base of the spine discharges its contents through the apertures and the canal in the interior of the spine. The structure of the dorsal spines is similar. There are no secretory glands imbedded in the membranes of the sacs; and the fluid must be secreted by their mucous membrane. The sacs are without an external muscular layer, and situated immediately below the thick loose skin which envelops the spines to their extremity; the ejection of the poison into a living animal, therefore, can only be effected, as in Synanceia, by the pressure to which the sac is subjected the moment the spine enters another body.

Finally, a singular apparatus found in many Siluroids may be mentioned in connection with the poison-organs, although its function is still problematical. Some of these fishes are armed with powerful pectoral spines and justly feared on account of the dangerous wounds they inflict; not a few of them possess, in addition to the pectoral spines, a sac with a more or less wide opening in the axil of the pectoral fin; and it does not seem improbable that it contains a fluid which may be introduced into a wound by means of the pectoral spine, which would be covered with it, like the barbed arrow-head of an Indian. However, whether this secretion is equally poisonous in all the species provided with that axillary sac, or whether it has poisonous qualities at all, is a question which can be decided by experiments only made with the living fishes.