274 G. V. NIKOL'SKII 



FEEDING ON INDIVIDUALS OF THE SAME SPECIES 



Accidental or regular consumption of individuals of the same species is 

 known to take place in many fish species; in most cases it is the large-sized 

 individuals which consume their own young (Klyuchareva, 1956). This mass 

 consumption of their own young varies rather strongly from year to year. 

 In years when the production of young is high but the food supply for large 

 fish unfavourable, the consumption of their own young by the adults 

 naturally decreases the density of the forthcoming generation. In some 

 species (cod, navaga, common and Balkhash perch and others) the fry provide 

 more than 50 per cent of the yearly consumption of food. The eating of the 

 young usually takes place after that period of development (usually the 

 period of transition from internal to external feeding) when the size of the 

 generation is being determined. Naturally feeding on the young is not only 

 a method o£ density regulation; in some species, e.g. in common perch, 

 the feeding on their own young provides food in water bodies where the 

 food supply for the adult fish is insufficient. Consuming its own fry, the 

 adult perch through its young eats such food as small zooplankton which it 

 is unable to assimilate directly. 



In the rivers of the Far East the salmon die after spawning and their 

 cadavers are well preserved till spring in the cold water. They then serve as 

 an important food for the young of some species of Far Eastern salmon (e.g. 

 the autumn form of chum salmon) during the river period of their life. But 

 perhaps of much greater importance for the increase of food supply of these 

 young, is not their direct consumption of parental cadavers, but the effect 

 of these latter as fertilizers of feeding grounds. In the places where many 

 cadavers of spawners accumulate in the rivers a rich fauna of the benthal 

 invertebrates develops in the next spring; while in the river the young 

 salmon exist partly on this fauna. As E. M. Krokhin has shown (i959)» the 

 amount of phosphates and plankton in the lakes of Kamchatka increase in 

 the years that follow those when large numbers of red salmon [Oncorhynchus 

 nerka Walb.) migrated into the lakes for spawning; an increase in the amount 

 of plankton food for the young takes place as a result of the fertilization of 

 the lakes by the cadavers. Thus, the generation of O. nerka which descends 

 from a large spawning stock fmds itself under more favourable conditions 

 of food supply and its survival rate is increased. 



This means that in spawning rivers of the Far East, the young salmon are 

 to some extent provided with food at the expense of the food resources of 

 the sea that have been accumulated in the bodies of their parents during the 

 period of their life in the sea (Vastnetsov, 1953). The feeding of the young of 

 the Far Eastern salmon on the parental cadavers is utihzed for practical 



