Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/255

 FISHERIES 245 takes place at the surface ; but with the cod family we believe the operation has not been so distinctly observed. The ova, however, are undoubtedly met with at the surface and at a short distance below it. Entirely subversive as these discoveries of Professor Sars are of the popular notions ubout fish-spawning, it is even more unexpected to find that both he and M. A. W. Malm of Gothenburg have independently ascertained that the ova of that essentially ground-fish the plaice (Pleuronectes platessa) follow the same rule of floating at the surface. Other kinds of float ing ova were also obtained by Sars, some of which he succeeded in hatching ; and he has completely identified the gurnard (Triyla) and the garfish (Bellone), in addition to those before mentioned. It is evident, then, that the iloating of fish ova during the development of the embryo must be taken as the general rule in several large and distinct families of sea fish. Sars has pointed out that the development takes place at the bottom in the case of those fishes especially whose ova are cemented together by a glutinous secretion, or fastened in lumps to foreign bodies, such as Algse, Hydroids, &c. lie mentions as examples of this, among others, the herring (Clupea), the capelan (Osmerus), the species of Coitus, Liparis, &c. It is particularly worthy of notice that, according to these observations of the Norwegian naturalists, all the important kinds of fish taken by our line fishermen and beam-trawlers, and the mackerel among such as are caught by the drift-nets, may be reasonably included among the species whose spawn floats at or near the surface of the sea, and their ova cannot therefore be liable to the slightest injury by any method of fishing which is carried on upon or near the ground. For if that bo the rule with the spawn of the cod and haddock there can hardly be a doubt about its being so likewise with the ova of ling, coal-fish, whiting, pollack, hake, and that northern species, the tusk, all belonging to the same family. Again, turbot, holibut, brill, soles, plaice, dabs, and flounders are all closely allied, and there can scarcely be a doubt that the same rule applies to all which Sars and Malm have established in the case of the plaice, one of the most typical of this group of fishes. The gurnard family must also be included in this category; the spawn of the red mullet, we believe, has been observed floating in aquariums; and the dory, from its close affinity to the mackerel, may be expected to follow the same rule. On the other hand, we know that the spawn of the herring is commonly found at the bottom, although it by no means follows that the parent fish is there when the ova are excluded ; for the full herring is frequently taken in drift nets which are very near the surface, and these nets are often covered with small lumps of spawn. At the same time the specific gravity of herring spawn is greater than water, and it sinks to the bottom sooner or later if nothing intercepts it. There is no evidence of its ever floating at or near the surface as is the case with that of the cod. In fact, the aggregation of the ova into masses of various sizes, and the glutinous substance in which the ova are embedded, by which they are enabled to adhere firmly to anything with which they may come in contact, point to their remaining in a fixed position during the process of development. It might have been anticipated that the other members of the herring family the pilchard and sprat, for instance would also have spawned on the ground, but, so far as we are aware, their ova have never been found there. Indeed, nothing is known of the spawning habits of the sprat, although this little fish lias the roe well developed in December or January, when it is found in the greatest abundance on our coast, and comes nearest to the shore. The spawning of the pilchard is a matter of some little interest. The late Mr Jonathan Couch, who probably devoted more time to the study of the habits of this fish than any other ichthyologist, states 1 his belief that the pilchard spawned at the surface, and the ova became mixed with a large quantity of tenacious mucus which spread out like a sheet on the water and kept them floating. If this should be confirmed, it will prove that even in the case of agglu tinated masses of ova, development may naturally take place in them far away from the bottom. There appears to be little doubt that the pilchard spawns far out at sea, as they are on chance occasions taken in spawning condi tion in the mackerel drift-nets early in the year ; and when, some months later, the shoals of pilchards approach the land the roe shows no signs of development. These circumstances favour the idea that pilchards are surface spawners, as believed by Mr Couch. There are several other kinds of edible fish of whose spawning habits we have no definite knowledge, but enough has been discovered of the habits of most of the fish which are valuable for the purposes of food, to show that there need be no anxiety about their spawn being destroyed by any of the methods of fishing in ordinary use. The only apparent exception to this statement is in the case of the herring, whose spawn it has been alleged has been destroyed by the beam-trawlers. But if the beam-trawlers wish to avoid tearing their nets in pieces, they must work where the ground is smooth; and in the few precise localities where it has been positively ascertained that the herring does spawn, the general character of the bottom is rough. That is the ground specially worked over by the line fisher men for haddock, cod, turbot, and other fishes, which come there in numbers for the sake of feeding on the herring spawn. There is a popular idea that all fish spawn is of a Vitality most delicate nature, and quickly loses its vitality if taken of spawn, out of the water for a short time, or at all knocked about. This is probably true in those cases in which the ova are separated from each other after exclusion, and float freely in the water ; but it is not so with the spawn of the her ring, or probably of other fish whose ova are embedded in a tenacious mucus. The experiments of Professor Allman and of Dr M Bain have shown that herring spawn does not readily lose its vitality under rough treatment, and may even be hatched out after having been exposed to most unnatural conditions. Professor Allman states in his Report to the Board of Fisheries at Edinburgh that some stones covered with spawn were taken from the sea by divers on the 1st of March 1862, not far from the Island of May. Some of this spawn was forwarded to him and came into his possession after being kept in only a small quantity of water for two entire days. He says : &quot;With the view of determining whether development would proceed in confinement, I placed some of this spawn in a glass jar with sea-water, exposing it in a window looking to the east. The several stages of development were regularly passed through, and on the 15th of March the embryo was fully formed, energetic movements were performed by it in the ovum, and it seemed ready to escape into the surrounding water. On the 16th some of the embryos had actually escaped, and were now about four-tenths of an inch in length. They were of crystalline transparency, and swam about with great activity, and with the remains of the yolk, reduced now to a very small volume, still adhering to them. The specific characters had, of course, not yet become established, and the little fish afforded no further evidence, beyond what we already possessed, to enable us to identify it with the young of the herring. The young fish lived nearly a month in confinement, but the specific characters were not even then sufficiently per fected to identify the fish with certainty. There could be no reasonable doubt, however, that the spawn was that of the herring. After some account of other discoveries of spawn, he thus concludes his report: &quot;It was shown by these experiments that the vitality of the iawn was in no way injured by detaching it from the spawning spawn History nf British Fishes, vol. iv. p. 81 (1865).