(p = 0.057). In models without maternal common environmental effects,
the estimated genetic correlation between direct and indirect genetic
effects on harvest weight was negative, indicating that traditional
selection will increase competition among individuals in the environment
of our study. We also found a strongly negative genetic correlation
between direct effects on survival and indirect effects on harvest
weight, indicating that individuals with better genes for survival had
group mates with lower growth rate in the competitive environment
that prevailed in our experiment. The confounding between maternal
common environmental effects and DGEs indicated that the one male
to two females nested mating design has limited power to estimate
the genetic parameters. We have to be aware that other mating designs
may allow more accurate estimation of genetic parameters, but may be
suboptimal for long-term genetic improvement in schemes where the
number of families is limited. Furthermore, more investigation is needed
on the implications of IGEs on commercial aquaculture industry,
where competition among