Proximate composition, reproductive development, and a test for trade-offsin captive sockeye salmon

Energy limitations during reproduction should lead to the evolution of adap tive patterns of energy use and should cause trade-offs in the expression o f different traits. We addressed these issues by measuring secondary sexual development, gonad investment, and proximate composition for sockeye salmo n Oncorhynchus nerka maturing in captivity. Each of the last 3 months befor e maturity was characterized by a different pattern of reproductive develop ment 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 decre ased (15.1% to 8.6% sex-specific values averaged), and viscera fat decrease d (23.9% to 16.7%). From July to August, male gonad mass did not change app reciably, but female gonad mass nearly doubled (to 5.5% of body mass). Musc le fat and viscera fat continued to decrease (to 6.0% and 8.8%, respectivel y), but muscle protein remained relatively constant. From August to maturit y (September-October), female gonad mass more than tripled (to 18.6% of bod y mass) and secondary sexual characters increased in linear dimension by as much as 20.0% (male snout length). Viscera fat continued to decline (to 3. 3%), but muscle fat did not decrease appreciably. The conservation of muscl e protein until after fat was depleted may postpone reductions in performan ce that would accompany muscle degeneration. Mass-specific energy decreased between June and maturity in muscle (9.5-5.6 kJ (.) g(-1)) and viscera (11 .2-4.9 kJ (.) g(-1)). We found no evidence for trade-offs in allocation bet ween stored somatic energy, the size of secondary sexual characters, and go nad investment. An important area requiring further research is the effect of variation in energy stores prior to maturity on reproductive development at maturity. This prebreeding energy variation may obscure phenotypic trad e-offs.