PLASMA-INSULIN, GLUCAGON, GLUCAGONLIKE PEPTIDE AND GLUCOSE-LEVELS IN RESPONSE TO FEEDING, STARVATION AND LIFE LONG RESTRICTED FEED RATION IN SALMONIDS

Plasma insulin, glucagon, glucagon-like peptide (GLP) and glucose were measured in samples taken from rainbow trout, Oncorhynchus mykiss. (1.5 years of age) before feeding and at selected times up to 9 days after feeding. The feed contained 21.7% carbohydrate (65% digestible) in the dry matter. The fish responded to feeding with an elevated plasma insulin level (p < 0.005) 0.5 h post-feeding, which may account for the unchanged plasma glucose levels. Twentyfour hours after feeding, plasma insulin level had returned to pre-feeding levels, while 4-9 days after feeding, a significant reduction compared to pre-feeding levels was observed (p < 0.001). During this period plasma glucose levels remained unchanged. The corresponding plasma glucagon or GLP levels showed no significant elevation in response to starvation, the plasma GLP concentration was even significantly reduced on days 4-9 post-feeding (p < 0.01-0.001). Atlantic salmon, Salmo salar, (3.5 years of age) fed a calculated satiation ration (RL = 100) throughout their lifetime had, in addition to a higher body weight, significantly higher plasma insulin (p < 0.005) glucagon (p < 0.0001) and GLP levels (p < 0.0001) than fish fed half the satiation ration. The plasma glucose levels were, however, not significant different between the groups.