We compare the developmental rate of six closely related hatchery strains of rainbow trout. Hatching time, morphological analysis, and the pattern of ontogenetic change in lactate dehydrogenase, malate dehydrogenase, glucosephosphate isomerase, and phosphoglucomutase activities indicate significant differences in developmental rate between strains. There is close concordance among the different measures of developmental rate. Strains with higher levels of heterozygosity, as estimated from electrophoretic analysis of 42 loci, developed faster than less heterozygous strains. The variation in developmental rate in these closely related strains indicates that there is substantial genetic variation affecting the developmental process in rainbow trout.Key words: development rate, intraspecific variation, rainbow trout.
