Effect of density on growth and survival of rainbow trout

Abstract

Groups of rainbow trout ( Salmo gairdneri) were kept at five different densities during an initial feeding period of 42 days and a subsequent growth period of 180 days. They were then kept at the same density for 55 days. Differences between groups in mean weights and mortality were found as early as the end of the initial feeding period. At the end of the 180-days growth period the differences in mean weight between density groups were large. Differences in condition ( K) factor were also found at the end of this period. Groups at high densities had the lowest growth rate and K factor. When groups were kept at the same density, those originally at high densities showed the highest relative growth. It is concluded that high densities depressed the growth rate, and that compensatory growth occurred when the densities were standardized. It is important to take density into account when ranking families or progeny groups for growth performance.