Effect of Food Quantity on Fecundity of Rainbow Trout, Salmo gairdneri

Studies of histology and development of rainbow trout ovaries indicate that the degree of follicular atresia is associated with degree of starvation during the maturation period. Experimental stocks raised under varying starvation regimes showed that the greater the starvation, the higher the proportion of maturing follicles which regressed. Thus the result was a lower number of eggs brought to maturity in starved fish.Observations on natural populations indicate wide differences in egg size, with corresponding inverse differences in egg number at maturity. Egg size is apparently not effected by diet, but rather through natural selection depending on intraspecific competition. There appeared to be little correlation between egg size and fish size, but some difference did exist between age classes. Variations in egg number are therefore attributable to fish size, egg size and adequacy of diet. Starvation has also a lasting effect on the proportion of a given age-class which matures.