Heterozygosity and components of fitness in a strain of rainbow trout

We examined the relationship between multilocus heterozygosity and several components of fitness in the Arlee strain of rainbow trout (Salmo gairdneri). There is a significant negative association between multilocus heterozygosity and standardized rate of oxygen consumption (VO2) in 168 fish produced from a pooled mating between 55 females and 60 males. Fish which are more heterozygous also tend to be longer, heavier and have a significantly greater condition factor than fish which are less heterozygous. However, no relationship is evident between VO2, weight, length, condition factor and multilocus heterozygosity within two full-sib families. These results indicate that the larger size of more heterozygous fish may partially be attributed to the increased metabolic efficiency in heterozygotes compared to homozygotes and that these differences may only be detectable at the population level. More heterozygous females of the same age also have larger eggs. Energy conversion may be more efficient in more heterozygous females resulting in the production of larger eggs. The prediction that fish with faster developmental rates are metabolically more efficient and, therefore, have lower VO2 was also tested. Earlier hatching fish from five families do not have significantly lower VO2 than their later hatching full-sibs.