Early insulin and glucagon response associated with food intake in a teleost, the striped bass (Morone saxatilis)

To determine the existence of preabsorptive reflex responses in fish, plasma glucose, insulin and glucagon were measured in striped bass (Morone saxatilis) pre-feeding (baseline: 0 min) and at five times post-feeding (5, 10, 20 and 40 min) following a 15 h fast. Two diets were fed, a basal agar-gel diet, and the agar-gel diet supplemented with a previously identified feeding stimulant mixture comprised of L-alanine, L-serine, betaine and inosine-5-monophosphate at equimolar concentrations (0.1 mol l). After 11 days, blood samples were obtained from the caudal vein. In fish fed the stimulant diet, plasma insulin increased at 5 and 10 min post-feeding but fish fed the basal diet had lower levels than baseline after 5, 10 and 20 min. Glucagon levels were increased in fish fed the stimulant diet at 0–10 min post-feeding, then decreased to levels similar to fish fed the basal diet. Glucose levels were elevated in both treatments post-feeding and were similar in both treatments. These results indicate that there is an early phase of reflex insulin and glucagon secretion in fish, shortly after the beginning of a meal, as has been described in mammals and birds. Furthermore, feed palatability may play an important role in insulin and glucagon secretion.