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An investigation of the regulation of reproductive development in pink salmon (Oncorhynchus gorbusha) in relation to the initiation of an off-year pink salmon run MacKinnon, Colin N.

Abstract

This study was undertaken to determine whether gonads of pink salmon (Oncorhynchus gorbuscha) could be stimulated by pelleted or injected salmon gonadotropin to reproductive maturity one year earlier than normal. This procedure, if successful, might be used in attempting to populate an "off" year cycle of pink salmon. In juvenile male pink salmon complete maturity was attained by September in the year of hatching with both pellet implantation (1x/3 weeks) and injection (thrice weekly) of 1.0 micrograms of chinook salmon (Oncorhynchus tshawytscha) gonadotropin per gram body weight. Time of onset of mitotic division of spermatogonia and rate of spermatogenesis were accelerated in the precociously mature testes. Similar doses of salmon gonadotropin injected at longer time intervals (1x/week, and 1x/2 weeks) resulted in a slower maturation. In females, acceleration of maturation was achieved in immature pink salmon by injection and pellet implantation of salmon gonadotropin. The primary yolk vesicle stage was achieved after 4 months of treatment with thrice weekly injections and 1x/3 week pellet implantations of 1.0 μg/gm body weight of salmon gonadotropin. Similar doses of salmon gonadotropin injected at longer time intervals (1x/week and 1x/2 weeks) resulted in a reduction in the rate of maturation. Large numbers of preovulatory corpora atretica were observed in all treated fish. The knowledge developed by this research formed part of a large scale co-operative program with two objectives. The pragmatic objective is to develop an "off" year pink salmon spawning population in Bear River which has no spawners in odd-numbered years. The scientific objective is to assess the value of adding "home stream" genetic material to the transplanted embryos and to evaluate two experimental techniques as to their effectiveness in providing "home stream" genes to the transplanted population. The approach was to fertilize eggs taken from fish of another river (Glendale River) with 1) spermatozoa from precocious Bear River males, 2) cryopreserved spermatozoa from Bear River males, and 3) spermatozoa from Glendale River males (control transplant group). The fertilization rate among eggs of the precocious Bear River male x donor Glendale female group was equal to the control group (Glendale River male x Glendale River female) and twice that of the cryopreserved Bear River male x Glendale female transplant group. The control group exhibited a higher developmental index (K[sub D]) and migrated about 6 days earlier than the other two groups which had 50% of their genetic complement from the Bear River stock.

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