Proximate Composition, Reproductive Development, and a Test for Trade-Offs in Captive Sockeye Salmon

Abstract

Abstract Energy limitations during reproduction should lead to the evolution of adaptive patterns of energy use and should cause trade-offs in the expression of different traits. We addressed these issues by measuring secondary sexual development, gonad investment, and proximate composition for sockeye salmon Oncorhynchus nerka maturing in captivity. Each of the last 3 months before maturity was characterized by a different pattern of reproductive development and energy use. From June to July, gonad mass increased (1.1% to 5.2% of male body mass; from 1.3% to 2.7% of female body mass), muscle fat decreased (15.1% to 8.6% sex-specific values averaged), and viscera fat decreased (23.9% to 16.7%). From July to August, male gonad mass did not change appreciably, but female gonad mass nearly doubled (to 5.5% of body mass). Muscle fat and viscera fat continued to decrease (to 6.0% and 8.8%, respectively), but muscle protein remained relatively constant. From August to maturity (September–October), female gonad ...