PROLONGATION OF THE LIFE SPAN OF KOKANEE SALMON (ONCORHYNCHUS NERKA KENNERLYI) BY CASTRATION BEFORE BEGINNING OF GONAD DEVELOPMENT

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Abstract
To ascertain whether or not there is a causal relationship between the spawning act and subsequent death of Pacific salmon, a large number of kokanee salmon (168) were castrated at 2 years of age while still completely immature. They were maintained in a rearing pond together with twice the number of unoperated controls. The castrates grew well and were indistinguishable from the controls until the fourth year when many of the males took on the morphological appearance of normally maturing salmon, exhibited degenerative changes and died. Regeneration of testicular tissue, usually very small in amount, was found to be present in these fish. The control kokanee all matured and died before the end of their fish year. A small group of castrates (21) were alive at this time, and continued to grow. Seven of them reached the eighth year of life and two survived until the ninth year. The last, a female, died at 8 years 6 months. The results of this experiment indicate that it is the maturation of gonadal tissue and not the actual spawning (at least in males) which leads to degeneration and death and that if sexual development is prevented by castration kokanee can survive well beyond the normal life span of this species.