Endocrine effects on nitrogen excretion in the euryhaline teleost, Salmo gairdnerii

Abstract

Several of the hormones known to be active in the induction of parr-smolt transformation and the migration of salmonids to salt water were administered to nonsmolt freshwater rainbow trout to assess their effects on the nitrogen excretion of fed and starved individuals. Somatotrophin and thyroxine decreased nitrogen excretion in the fed fish, whereas cortisol was without effect. In the starved fish, cortisol caused an increase in the excretion of nitrogen, but somatotrophin and thyroxine were ineffective. Simultaneous administration of cortisol and somatotrophin to nonsmolt freshwater fish produced a pattern of nitrogen excretion similar to that observed in freshwater smolt and salt water fish, decreasing the nitrogen excretion of fed fish but inducing an increase in starved fish. It is suggested that the hormones responsible for the regulation of euryhalinity in rainbow trout have an important influence on the different specific growth and nitrogen excretion rates found at the various stages in its life history.