Evidence of differences in growth and food intake regulation in different genetic strains of channel catfish

Abstract

Norris and USDA‐103 strains of channel catfish Ictalurus punctatus were compared for growth rate and food conversion ratio under satiation feeding and restricted feeding (1% body weight day−1) regimes. At the start of the experiment Norris fish weighed 2·8 g, USDA‐103 fish weighed 14·0 g. Therefore, a regression of the loge of specific growth rate against the loge of mean body size with an empirically derived fixed slope of ‐0·37 was used to compare growth rates. Under both feeding regimes the USDA‐103 strain had faster specific growth rates and more efficient food conversion. In subsequent studies, voluntary food intake of size matched fish (60 g average) from these two strains was compared using a radiographic method. Fish were acclimatized to tank conditions for 3 weeks prior to voluntary food intake measurement. Half of the groups were deprived of food for 2 days prior to food intake measurement, while the remaining groups were fed 1% body weight day−1. The USDA‐103 strain fish ate significantly more food and grew faster than the Norris strain fish. Previously fasted Norris fish subsequently ate more than their fed counterparts, whereas the fed USDA‐103 fish consumed more food than the fasted USDA‐103 group. When the USDA‐103 strain fish were deprived of food for 4, 2 or 0 days, all groups subsequently consumed between 4·5 and 5·0% of body weight in one meal. The USDA‐103 fish, unlike the Norris fish were not stimulated to consume more after short‐duration fasting. Taken together, these results suggest that there are genetic differences in growth, food conversion ratio and regulation of food intake between Norris and USDA‐103 strains.