Three strains [domestic (D), Laval (L) and Rupert (R)] of brook charr Salvelinus fontinalis and their reciprocal hybrids were submitted to transport stress to measure stress resistance. Primary (cortisol) and secondary (glucose, osmolality and haematocrit) stress responses were
measured for each cross. Significant heritabilities were observed for both levels of stress response, with mean ±s.e. heritability (h2) = 0·60 ± 0·20 for plasma cortisol and 0·61 ± 0·20 for plasma glucose.
There were strain differences whereby the R strain was the least sensitive to stress at the primary and secondary levels. No heterosis was detected, and only one case of outbreeding depression was present. The outbreeding depression was observed in the D♀R♂
hybrid, which had a 27% increase of plasma glucose compared to parental strains. The D♀R♂ and R♀L♂ hybrids had more pronounced variations (increase or decrease) in plasma osmolality than their respective parental strains,
but these variations were difficult to relate definitively with the potential secondary stress response. These results indicate a strong potential for genetic improvement in the stress response to transport with the use of purebred crosses while hybridization has little value in this regard.