Maternal effects in the inheritance of cold tolerance in blue tilapia (Oreochromis aureus)

In accordance with their tropical origin, the optimal water temperature for most tilapia species is between 25 and 28 A degrees C. The lethal temperature varies as a function of environmental effects, individual fish histories and genetic effects; however, the genetic basis of cold tolerance in tilapia has not been investigated in detail. Blue tilapia (Oreochromis aureus) is considered as one of the most cold-tolerant tilapia species, and, in this study, we have used a fish from a three-generation selective breeding program for enhanced cold tolerance. Four crosses within and between resistant and sensitive fish were used in this study. Forty families were challenged for cold tolerance, and a strong maternal effect was observed in two consecutive experiments. Expression patterns of the mitochondrial ATP6 gene were strongly correlated with cold tolerance; however, an analysis that applied an individual animal model restricted maximum likelihood on a three-generation pedigree, implies that an epigenetic effect rather than mitochondrial inheritance is the main source of the observed maternal effect. This study demonstrates that maternal effects can play a significant role in the inheritance of cold tolerance and that maternally-transferred genetic components should be targeted when adaptation to low temperature is studied in tilapia.