Heritable variation in swimming performance in Nile tilapia (Oreochromis niloticus) and negative genetic correlations with growth and harvest weight

Nile tilapia is predominantly produced in smallholder ponds without aeration. We hypothesize that Nile tilapia with high oxygen uptake efficiency (O 2 UE) may perform better under these conditions than Nile tilapia with low O 2 UE. Critical swimming speed ( U crit , in cm s −1 ) is a potential indicator for O 2 UE. Our objectives were to estimate variance components for U crit and fish size at swim testing early in life, and genetic correlations ( r g ) between U crit with harvest weight (HW) and daily growth coefficient (DGC) later after grow-out in a non-aerated pond. Substantial heritability was found for absolute U crit (0.48). The estimated r g between absolute U crit and fish size at testing were all strong and positive (range 0.72–0.83). The estimated r g between absolute U crit and HW, and absolute U crit and DGC were − 0.21 and − 0.63 respectively, indicating that fish with higher absolute U crit had lower growth in the non-aerated pond as compared to fish with lower absolute U crit . These results suggest a juvenile trade-off between swimming and growth performance where fish with high U crit early in life show slower growth later under conditions of limited oxygen availability. We conclude that U crit in Nile tilapia is heritable and can be used to predict growth performance.