Plasma glucagon levels in different species of fish.

Plasma glucagon levels in 11 different teleosts and in dogfish were evaluated using an adapted classical mammalian radioimmunoassay (RIA). The values obtained are considered relative; sensitivity was inferior to the original method, but the validation experiment results are acceptable. The mean value of the coefficient of the variation for interassay was 6% and for intraassay 4%, recovery was 98%, and a good linearity in the dilution test was found. Some species (Sparus aurata and cyprinids) presented high plasma glucagon concentrations (0.50-1.60 ng/ml) versus the lower levels (0.08-0.40 ng/ml) found in salmonids and others, and the lowest in dogfish (0.02-0.20 ng/ml). A positive correlation (P less than 0.02) between insulin and glucagon plasma levels was found in different species. The low levels obtained in all parameters analyzed in the selachian were remarkable. This adapted RIA could serve as a useful tool in amplifying knowledge on the endocrine pancreatic response in fish in different biological situations.