ENDOCRINE AND OTHER PHYSIOLOGICAL FACTORS ASSOCIATED WITH THE SPAWNING MIGRATION OF PACIFIC SALMON (ONCORHYNCHUS SPP.) AND THE STEELHEAD TROUT (SALMO GAIRDNERI)

31 pagesTwo genera of fishes in the family Salmonidae have stimulated considerable biological interest on the Pacific coast of North America. The anadromous life histories of both the Pacific salmons (Oncorhynchus spp.) and the migratory rainbow trout (Salmo gairdneri) have provided many research opportunities during the past several decades. Although the life histories of these two genera of fishes are quite similar, a basic difference is reflected in their post-spawning mortalities. While the universal post-spawning mortality of adult Pacific salmon restricts them to a single spawning, some of the anadromous trout may spawn repeatedly, but post-spawning mortality may amount to as much as 50%. The ability of the steelhead trout to survive under the same environmental stresses that result in the death of Pacific salmon represents -- a still somewhat Puzzling species difference of vertebrate physiological uniqueness. This paper will attempt to review current and past work on this question of survival vs. death in these anadromous fishes which comprise one of our most valuable local natural resources