Plasma insulin levels in teleosts determined by a charcoal-separation radioimmunoassay technique.

Abstract

Plasma insulin levels in a variety of teleosts were determined by a charcoal-separation radioimmunoassay technique employing cod insulin components. The method was satisfactory for all species studied but was more sensitive for cod and less so for trout, dab, and eel, while the values for plaice and pike were at the lower limits of sensitivity of the assay. Plasma insulin and glucose levels in cannulated European silver eels, sampled over 4 days, were both elevated initially but subsequently fell to stable, lower values after 2 days. Plasma insulin and amino-acid nitrogen levels of fed rainbow trout and cod were significantly higher than for starved animals while the correlation of plasma insulin with glucose was less apparent. The study illustrates the need for careful consideration of the blood-sampling technique to be used and of the nutritional state of the fish whose plasma insulin is to be measured.