Effect of density on growth and survival of artificially reared Atlantic salmon

Groups of salmon (Salmo salar) from two localities were kept at five different densities during the initial feeding period of 42 days and a subsequent growth period of 205 days. They were then kept at the same density for 95 days. Differences in mean weight between fish from different localities were found as early as the end of the initial feeding period. No marked differences were found between mean weights of fish held at different densities during the initial feeding period, while the mortality rate of fry decreased with higher densities for both strains. At the end of the 205-day growth period the differences in mean weight between strains and between density groups within a strain were large. Significant interaction between locality and density was also found. Part of this interaction is due to scale effects.When groups were kept at the same density, those originally at high densities showed the highest relative growth, and also had the highest K-factor at the end of this period. 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 in selective breeding trials.