The Competition for Food between Triploids and Diploids and its Effect on the Growth of Triploids in Rainbow Trout

Abstract

We compared feeding and growth potential between diploid and triploid rainbow trout Oncorhynchus mykiss under communal and separate rearing conditions. Under communal rearing conditions and at 100 % of the daily feeding rate of dry food recommended by Leitritz, significant differences in the body weight between diploid and triploid were noted from 16 weeks after the start of the feeding trial. At twenty weeks, the mean body weight of diploid and triploid trout were 18.62 ± 0.21 (SEM) and 17.38 ± 0.22 g, respectively. When using 50% or 30% of the feeding amounts recommended by Leitritz, there was a proportional decrease in the growth rate of triploids in comparison with that of diploids as feeding amounts decreased. Under separate rearing conditions and at 100 % feeding rate, triploid showed better growth than diploid. A comparison of the amount of food taken by diploid and triploid trout in communal rearing conditions revealed a progressive decrease in the food available for the triploids with decreased feeding rates. The growth hormone levels in plasma in both ploidies were not significantly different. These results suggest that the decreasing growth rates of triploids reared together with diploids was due to poor performance of the former in the competition for food.