Translation Series No. 266

d ARCHIVES FISHERIES RESEARCH BOARD OF CANADA Translation Series No. 266 DIFFERENCES IN THE BIOLOGY OF REPRODUCTION AND DEVELOPMENT OF RESIDUAL OR DWARF SOCKEYE AND ANADROMOUS SOCKEYE (ONCORHYNCHUS NERKA (WALBAUM)). By A. I. Smirnov Original title: Otlichiiâ v biologii razmnozhens.iâ i razvitii ostatochnoi ili karlikovoi i prokhodnoi nerki [Oncorhynchus nerka (Walbaum)]. Fromô Nauchnye Doklady Vysshei Shkoly, Biologicheskie Nauki, No. 3, pp. 59065, 1959. Preliminary translation by W. E. Ricker Distributed by the Fisheries Research Board of Canada Biological Station, Nanaimo, B. C. 1960 At the present time quite a variety of material has been collected indicating wide intraspecific variability in salmonfl an example of this being the recognition of hiemal and vernal races9 and local stocks, From both a theoretical and a practical point of view j_t is of interest to discover whether intraspecific diffe-r® ences occur only in the final stages of the growthfl or whether they are evident throughout other stages of developmentfl even the- very earliest. It can be taken for granted that good material for shedding light on this question is afforded by the species which include both anadromous and freshwater forms a such forms being particularly sharply distinguished from each other. During 1956 and 1957 the author studied the development of anadromous and the so-called residual Costatochna â] or dwarf sockeye salmon (Oncorhynchus nerka (Walbaum)). The work was done at the Paratunka Stàtion of the Kamchatka bivision of the Pacific Research Institute for Fisheries and Oceanography (TINRO)fl which is situated on Lake Dalneen the latter being connected by means of a small river of the same name which drains from it to the bisin of the Paratunka, and thence flows into the Gulf of Avachin. The characteristics of the development of anadromous sockeye have already been briefly described (Smirnov, l95$). In the present article some characteristics of the reproduction and development of the dwarf form are outlined, and a comparison is made with the anadromous form. According to the observations of F. V. Krogius2^ males pre® dominate in number among the residual sockeye9 and they mature at ages from 2+ to 4+ 9 most frequently at 3+; the females for the most part mature one year later, most of ^hem at age 1++, and they have a fecundity of about 500 eggs, Ripe dwarf males are observed from the beginning of September and mingle with the anadromous sockeye during spawning, but the dwarf females mature about a month later. Both the male and the female dwarf sockeye feed up to the time of maturing9 whereas anadromous sockeye cease feeding at the mouths of the rivers, that is, quite a long time before spawning. 1The success of the work was greatly facilitated by the efforts of F. V. Krogius and E. M. Krokhin, to whom the author extends his heartfelt thanks. 2F, V. Krogius, 1952, Materials on the biology of the sockeye salmon Oncorhynchus nerka (Walbaum), Fondy Kamchatskovo otdelenii Tikhookeanskovo n,-i-, in-ta rybn. khoz-va i okeanogr, 3 [Here and later peripe" is used to translate tekuchii, literally '1running"p presumably meaning fish with freely flowing milt or eggs.] - 2 - In the years of our observations ripe dwarf male skeye were encountered beginning in the second 5-day period of September, whereas the first ripe females were caught only between the 6th and 10th of October. Judging by the capture of females with only a small quantity of eggs remaining, spawning lasted up to the beginning of November. In the same years the summer anadromous sockeye began spawning in the last 5-day period of August and they finished in the last 10-day period of October. The beginning of their spawning [page 60] coincided with a marked warming of the upper layers of water in the lake and also of the springs (ground water) the daily mean temperature of the water at the source of the river [outlet of the lake?] exceeded 14 0 9 and in the spring which supplied water for our hatching apparatus it was 4'. The spawning of the dwarf sockeye began when there had been some cooling of the upper layers of water (mean daily temperature at the source of the river fell to 5 or -6") and when the temperature of the ground waters began to decrease. Thus the completion of the maturation of the dwarf females and their spawning takes place at a lower temperature [than that of the anadromous fish]. The spawning place of dwarf sockeye has not been exactly determined. In earlier years and during the period of our work in Kamchatka no nest construction by them was observed in the shallow littoral area of the lake in places where the anadromous summer form spawns. Above Lake Dalnee there are no tributary bodies of water where spawning might take place, as has been observed for the kokanee type of dwarf sockeye [zhilaia karlikovafà nerka] in Lake Kronotsk and in certain American lakes (V. V. Ohernavin, 1921; E. M. Krokhin and F. V. Krogius, 1936; I. Fraser and A. Pollit, 1951); while in the river flowing from the lake no emigration of dwarf females for spawning has been observed. Inas- much as during the spawning period ripe dwarf females were cap- tured in fixed nets, placed near the shore, we may assume that they laid their eggs in the littoral region of the lake but in deeper water than the anadromous sockeye. Ripe dwarf individuals in Lake Dalnee are easily distinguished by external appearance from anadromous sockeye. It is widely known that mature males and females of anadromous sockeye assume an intense red colour, while their scales lose their luster and become deeply buried in the skin; the body of the males before maturity becomes compressed, on the back there appears a great hump, the jaws become greatly lengthened and tusk-like teeth grow out from them. Pre-spawning changes in the form of the body, skeleton and teeth of dwarf sockeye of Lake Dalnee are quite small (Fig. 1). The body covering of the dwarf sockeye also changes very little. It retains a distinct silveriness, while the scales are only slightly embedded in the skin and are easily removed. The general tone of the colour of the ripe spawners is dark grey. Dwarf sockeye males are usually of a dark olive shade on the body, with a weak narrow rosy stripe along the midline; among the females these marks [page 61] as a rule are lacking and a metallic blue-violet shade prevails. On the head and back of the dwarf 3 spawners there are weakly developed fine dark spots; similar spots are more clearly developed on the dorsal and caudal fins. On certain females there may be seen the rosy stripe along the lateral line which is characteristic of males, and an olive shade on the back. These characters do not occur on all of the males Ceither7. Becâ.use of this variability in colour, and the absence of differences in body form, it is not possible to distinguish the sex of some of the dwarf individuals by external characters. An analysis of the pre-spawning changes in the body covering of Pacific salmons, and the conditions under which they appear, has led me to the conclusion that they have an important adaptive function, permitting intensification of the dermal respiration which is necessary under the new environmental conditions and the changed physiological. circumstances for the spawners ( Smirnov, 1959)o Dwarf spawners, because of their small size, have a relatively large . body surface; therefore, among them it would seem that the necessa:ry increase in level of dermal respiration is achieved with-less change in structure and colour of the body covering. In addition , the spawning medium of the dwarf sockeye is not so radically different from the medium in which they feed during their active life; therefore the transition to the place of reproduction does not require such radical adaptive changes in the organism as takes place in the anadromous sockeye. Judging by the specimens which E. M. Krokhin has kindly provided me with, the Lake Kronotsk kokanee change more9 during the period of their maturation, than do the Lake Dalnee dwarf sockeye; spawning individuals are brightly coloured, they have heavier teeth and in the males a distinct hump is developed. As was remarked earlier, the stock of Kronotsk kokanee leaves the lake for spawning and enters the river and springs9,corresponding to this more severe change in spawning environment ( as compared with that of the Lake D.alnee dwarf sockeye) among them there occurs a more important change in the whole organism before spawning. Such an ecological -int,erp.retation of the causes of the differences in the degree of development of the somcalled breeding colours [brachnyi nariad], among different stocks of trout, has already been suggested (V. V. Chernavin, 1921). As we have seen, this approach is applicable also to our problem; however it is clear that a more detailed analysis of the causes of the development of pre-spawning changes in the dwarf and the anadromous forms of sockeye will require the undertaking of special physiological studies. The majority of the dwarf males which were at my disposal were ripe, and data on the weight of their gonads, of course, are too low. The observed variation in weight of the testes is from 3.6 to 6.6% of the body weight. The maximum weight was observed in a male of stage IV of maturity ( weight 17$ g) whose testes weighed 11.7 g. According to the data of I. V. Kizevetter (194$), among,semi-mature anadromous sockeye the weight of the gonads varies among the males.from 2 to 6%, and among the females from 7 to 12% of the body weight.

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