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RECENT ADDITIONS TO OUR KNOWLEDGE OF

THE NATURAL HISTORY OF SOME

DEVONSHIRE SEA FISHES.

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In the course of the last ten years, even within the last five, in consequence of the great activity which has been displayed in this department of research, remarkable progress has been made in the study of the life-histories of marine fishes, and of their relations to the conditions under which they live. The activity to which I refer has numerous centres in nearly all civilized countries, and these centres are laboratories expressly organized for marine biological research. Such laboratories are either wholly or partly devoted to the investigation of the natural history of those marine species of fish which form an important part of the national food supply, and in Britain and other countries with an extensive coast-line, form the basis of one of the great trades or industries of the population. It is curious to contrast our meagre knowledge of the natural history of sea fishes, constituting as they do an important item of national wealth, with the elaborate and detailed knowledge available concerning insects which have comparatively little economic importance. Of course, there are some insects of practical interest, because they are injurious to crops, but there are others, like ants and butterflies, which have only the slightest effect upon agricultural industries, and which have been studied by entomologists for centuries until every detail of their organization and life is familiar. On the other hand, only a few years ago, the mode and place of development of our most important food-fishes, except the herring, was absolutely unknown. In place of scientific knowledge we had romantic and imaginary legends, such as the story that the herrings came down in hordes on an annual migration from the Arctic seas. Whitebait was described as a separate species. Males and females of a single species were described under different specific names, as though belonging to different kinds of fish, and so on. At the present time, although we know somewhat more, there is still much to be discovered, many questions to be answered. The reason of these facts is not far to seek: it lies simply in the enormously greater difficulty attending the study of animals that live in the sea. Insects are always with us, they force themselves on our attention, and the apparatus required to study them either in the living or dead state is neither costly nor cumbrous. But, in studying a marine animal, man is at a great disadvantage. He cannot see what takes place in the sea, he can only pursue his investigations from a ship. Fishermen are not naturalists, and naturalists have, until recent years, had few opportunities of carrying out their methods of study on board ship. Now that they have procured themselves such opportunities they have not been slow to remove some of the obscurity under which the natural history of fishes was long concealed. On the present occasion I propose merely to give a brief summary of the facts that have been established by the work of the Marine Biological Laboratory at Plymouth, concerning some of the fishes which are brought to market at that port.

The pilchard and herring belong to the same family of fishes, namely, Clupeidae, to which also belong the sprat and the shads. The herring was the first marine food-fish whose eggs were identified and studied, and it was well known and definitely proved that the spawn of the herring formed adhesive clumps which adhered to stones, weed, hydroids, or other objects on the sea-bottom. It was also known that shoals of herring annually visited particular areas, and deposited their spawn there. Although Sars proved in Norway that the eggs of the cod were buoyant and nonadhesive, and were suspended separately in the surface waters of the sea, it was natural to suppose that the eggs of the sprat and pilchard would prove to resemble those of the herring. However, in 1887, a German naturalist, Hensen, proved that the eggs of the sprat were pelagic, i.e., buoyant and transparent. As for the pilchard, Couch, in 1865, stated that its spawn was kept floating in a sheet of tenacious

or jelly, which has been shown to be erroneous. Matthias Dunn, of Mevagissey, stated, in 1871, that he pressed ripe spawn from a pilchard into a bucket of sea water, and that it floated at the top in the form of transparent globules, an observation which has been proved by corroborative evidence to have been perfectly correct. In 1888, an Italian naturalist at Naples, described a floating ovum, which he believed to belong to the sardine, and which he obtained from the sea. At Plymouth I have taken similar eggs from the sea, and have compared them with ripe eggs squeezed from the pilchard, and shown that they are the same. The spawning pilchards are caught in small numbers in the mackerel nets in June and July, at a considerable distance from the coast, but artificial fertilization has never yet been carried out. I have not obtained ripe males and ripe females at the same time. It is not easy to determine definite limits for the spawning period. I have received ripe specimens of the fish at various times, and have obtained the developing eggs from the sea at various times, and judging from these data, I conclude that the spawning period lasts from the end of May to the end of October.

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The young larval pilchards are to be caught with a fine meshed net in July : these are different from the adult, being very slender and quite transparent. Gradually they assume the silvery livery of the adult, and pass into what Devonshire fishermen call britt, the stage corresponding to white bait, similar to the adult except that they are only 11 to 3 inches long. At this stage they are largely devoured by mackerel in November, and are found in mackerels' stomachs.

There is a good evidence for believing that the pilchard of one year old is not adult, but varies from 5 to 6 inches in length, and in weight from half an ounce to an ounce, while adult pilchards are 8 to 9 or 10 inches long and weigh 3 to 5 oz. In November, 1891, we obtained in small meshed nets a large number of such small pilchards, and it is probable that they could be caught in summer, from May to November. But small-meshed drift nets are not used on the Devonshire or Cornish coasts, and these fish are therefore net taken. Off the French coast from Brest south to La Rochelle, the regular sardine fishery is carried on for the capture of such young pilchards. The adult pilchard is however caught on the French coast in autumn and winter as on the Cornish coast, and there is no doubt whatever that the French sardine as preserved in tins is the young of the pilchard.

The pilchard begins to breed when it is two years old, though probably only a proportion of individuals breed at this age, many not reaching sexual maturity until the end of their third year.

The pilchard like other fishes similar in habits, such as the herring and mackerel, used to be considered a migratory fish, and it is still so considered by fishermen. I do not wish to say that it is not migratory, but naturalists are now able to form a different conception of the habits of such fish, best expressed by saying they are pelagic. They feed in midwater on minute animals, and are always moving about in shoals. But their range is probably limited: the pilchard of the Cornish coast may wander to the French coast, but it probably does not reach the Spanish coast, and the sardine of the Mediterranean is certainly a separate race; nor does the pilchard extend to true oceanic waters, beyond the 100 fm. line.

The family Pleuronectidae is as important to our seafisheries as that of the Clupeidae, and I will just touch upon a few of the points which have recently been made out concerning this family. It is quite an old story now, that the eggs of all the species are pelagic. The eggs of the sole were first identified with complete certainty at Plymouth. They have been artificially fertilized with success several times at our Laboratory in small numbers, but an unexpected difficulty was found to prevent the performance of that operation on a large scale, namely, the extremely small size of the testes, and the impossibility of getting a large supply of milt from the male fish. The young of the flat-fishes when first hatched are transparent and symmetrical, and when they are a few weeks old their metamorphosis commences, one eye passing round to the opposite side of the body and the blind side becoming colourless. When this change commences in the sole, flounder, plaice, dab, and merrysole, the little fish are only about half an inch long, and they soon cease to swim at the surface. But the young turbot and brill are very different; they have an air-bladder during the period of transition, and swim at the very surface of the sea, often being washed into harbours or docks with the tide. They also reach a considerable size before their metamorphosis is complete, some specimens in this condition being as much as 11 inches long. After this stage the air-bladder entirely disappears.

There are interesting differences in the distribution of young flat fishes in the first year of their age, after they have begun to live on the sea-bottom like their parents, differences which do not completely correspond to those in the distribution of the adult fish. Thus young flounders, plaice, soles, turbot, and brill, are all found in shallow water, in summer VOL. XXIV.

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and autumn. To some extent they ascend estuaries; this is particularly true of the flounder, dab, and plaice. On the other hand the young of the thick-back, Solea variegata has been found only in deep water, over 20 fathoms. The young of the merrysole, Pleuronectes microcephalus, though it is so common in the adult condition, I have never found at all under 6 inches in length. Although the plaice and merrysole are two species of the same genus, it would seem that the young of the latter are reared in deep water beyond the 30 fathom line, while those of the plaice are found in abundance in water from two to ten fathoms. The young of another species again, Pleuronectes limanda, the dab, are found at all depths, from shallow water in estuaries and in Plymouth Sound, up to 30 or 40 fathoms.

Until the last two or three years practically nothing was known concerning the rate of growth of flat-fishes. I have made a number of observations on various species in connection with this question, both on specimens collected at sea, and specimens reared from the larval condition in the aquarium. The most complete experiment in rearing was made with flounders. I have found that both in the natural condition and in confinement the rate of growth is extraordinarily variable in different individuals, even allowing somewhat for the length of the spawning period, which extends over about three months. Thus specimens of the flounder, obtained on May 7th, 1890, were little more or less than half an inch; measured on April 4th, 1891, although kept during the

year in the same tank, they varied from 1.6 to 60 inches in length. Specimens are taken at sea during the spawning period, none of which can therefore be less than a year old, which show a similar variation in size. At two years of age some of my captive flounders became sexually mature, and eggs and milt were obtained from them. But the ripe specimens were only 19 per cent of the whole number, and the rest probably would become mature in the following year, when three years old. It may be that the course of events in specimens in the free state in the sea is different, but observations on specimens taken at sea tend to show that it is the same. The ripe females reared in captivity varied in size from 8.4 to 10.5 in., the males from 6:4 to 9.2 inches, and these sizes correspond closely with that of the smallest mature specimens taken at sea. The conclusion is that flat-fishes when they begin to breed are two or three years old, and that when they reach the size of large specimens of their species they are four or

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