Enlarged fatty livers of small juvenile cod: A comparison of laboratory-cultured and wild juveniles

Large juveniles and adult cod Gadus morhua develop enlarged fatty livers when fed high-energy lipid-rich diets in captivity; however, little is known of the partitioning of growth energy of small juveniles. This study compared simple indices of condition of laboratory-cultured and wild juvenile cod of similar size that consumed high-energy, lipid-rich food to determine whether small juveniles develop enlarged fatty livers in captivity. Cultured cod developed enlarged fatty livers. The hepatosomatic index (I(H)) and condition factor of cultured cod were significantly higher and tissue water contents were significantly lower than in wild cod. Cultured cod also exhibited significantly higher muscle mass at length. Cod of similar age exhibited a high range in body size, high coefficient of variation in size and the I(H) was correlated positively with body size indicating that a size-selective social hierarchy had developed in the laboratory. In contrast, the I(H) of wild cod was correlated negatively with body size, supplying evidence of high utilization of dietary lipids by larger juveniles in association with increased metabolic expenditure when feeding on small prey items.