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

Norris and USDA-103 strains of channel catfish Ictalurus punctatus were com pared for growth rate and food conversion ratio under satiation feeding and restricted feeding (1% body weight day(-1)) regimes. Al the start of the e xperiment Norris fish weighed 2.8 g, USDA-103 fish weighed 14.0 g. Therefor e, a regression of the log(e) of specific growth rate against the log(e) of mean body size with an empirically derived fixed slope of -0.37 was used t o compare growth rates. Under both feeding regimes the USDA-103 strain had faster specific growth rates and more efficient food conversion. In subsequ ent studies, voluntary food intake of size matched fish (60 g average) from these two strains was compared using a radiographic method. Fish were accl imatized to tank conditions for 3 weeks prior to voluntary food intake meas urement. 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. 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 f ood than the fasted USDA-103 group. When the USDA-103 strain fish were depr ived 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 Norri s fish were not stimulated to consume more after short-duration fasting. Ta ken together, these results suggest that there are genetic differences in g rowth, food conversion ratio and regulation of food intake between Norris a nd USDA-103 strains. (C) 1999 The Fisheries Society of the British Isles.