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Effect of food quantity on the fecundity of Kamloops trout, salmo gairdneri kamloops Jordan Scott, David Paul

Abstract

Tests showed that, in Kamloops trout, Salmo gairdneri kamloops Jordan, egg number produced at spawning is dependent on egg size for fish of a given length. Mean egg size in trout from Paul lake was considerably smaller than that of Penask lake trout. The difference is associated with natural selection pressures of low and high population densities, respectively. Egg number was inversely correlated with egg size in all samples. Pew differences were found between age classes within the natural populations. Starvation during early ovarian maturation produced a reduction in numbers of eggs shed at spawning. Experimental starvation treatments of hatchery trout indicated that increasing degrees of starvation resulted in commensurately fewer eggs reaching maturity. Pull diet conditions for the remainder of maturation resulted in no compensatory change in egg size. Maturing ovaries and stomach content volumes from trout reared naturally indicated a positive correlation between reduced food intake and increased follicular degeneration. Variations in egg number are therefore attributable to differences in egg size, fish size and adequacy of food supply. Egg size is apparently genetically controlled. Direct reduction of fecundity by starvation has an adaptive value in partially limiting population density.

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