Seasonal variations of insulin and some metabolites in dogfish plasma, Scyliorhinus canicula, L.

Plasma levels in insulin, glucose, ketone bodies, and lactate were analyzed during a 1-year period in the lesser spotted dogfish (Scyliorhinus canicula) in captivity. Plasma insulin levels fluctuated similarly for both sexes. The highest insulin levels were found during late prespawning (from January to March) and another increase was observed during the active feeding period (September and October). During the spawning period, insulin decreased and in the postspawning period the lowest values were reached. Glucose, however, showed a different trend. It was at a minimum in late prespawning and it reached its highest values in postspawning. It decreased again in September and October. Plasma ketone body levels were highest in late prespawning and could be considered as an alternative energy source for this hypoglycemic period. In the summer months plasma lactate levels rose, with maximum levels occurring in July.