Response of cholecystokinin and digestive enzyme mRNA levels to various feed ingredients in yellowtail Seriola quinqueradiata

Cholecystokinin (CCK) is the key regulator hormone that stimulates the secretion of digestive pancreatic enzymes in vertebrates. In fish, little is known about the mechanism of induction of CCK in the digestive tract by feed ingredients. To investigate the response of CCK and digestive enzymes to fish feed ingredients in yellowtail Seriola quinqueradiata, we performed a number of experiments in which we measured the mRNA levels of CCK, trypsin, and lipase after oral administration of a single bolus of the ingredients. We administered fish meal and fish oil in experiment 1; high and low concentrations of fish meal in experiment 2; and five different dietary protein sources (fish meal, soybean meal, soy protein concentrate, corn gluten meal, and glutamic acid fermentation by-products) in experiment 3. In experiments 1 and 3, only fish meal significantly increased the mRNA levels of CCK and digestive enzyme. In experiment 2, a high concentration of fish meal 20?% (w/v)] significantly increased CCK and trypsin mRNA levels, but a low concentration of fish meal 1?% (w/v)] did not. These results suggest that high concentrations of fish meal (the protein source in fish feed) has the most potent effect on stimulation of CCK synthesis and secretion of digestive enzymes in yellowtail.