Measurement of channel catfish (Ictalurus punctatus) plasma insulin in species-specific radioimmunoassay

A single antibody, equilibrium, species specific radioimmunoassay (RIA) for catfish insulin was developed and validated for measurements of plasma levels of insulin in juvenile and adult channel catfish. The RIA appeared to be sensitive (20 pg/tube) and stable with intra-assay coefficient of variation between 5.7% and 3.1% and inter-assay coefficient of variation of 6.5%. The blood was collected from two strains of catfish, USDA 103 and Norris, which differ in food consumption and growth rates, the former strain consuming more food and growing faster (Silverstein et al. 1999). The experiments conducted from December to May included fasting and feeding periods from 5 to 14 days as well as either intravenous or intraperitoneal administration of glucagon-like peptide known for its anorexic effect in both mammals and fish (Silverstein et al. 2001). As in other piscine species studied before, fed fish had higher plasma insulin content than food-deprived fish. Feeding status prevailed over other treatments as the primary physiological factor determining circulating plasma insulin levels.