Cholecystokinin and gastrin-releasing peptide differentially inhibit appetite of rainbow trout

The appetite in fish is a multifaceted phenomenon that comprises specialized interactions between brain and peripheral signals, and as a result, appetite is either stimulated or inhibited. Cholecystokinin (Cck) and gastrin-releasing peptide (Grp) are two postprandially released gastrointestinal peptide hormones that affect feed intake in fish. As the stimulatory or inhibitory effects of hormones can vary in duration and strength, making the nature of hormone effects dynamic, we modelled the dynamics of Cck and Grp using a direct, non-stressful approach. Fish were hormonally treated through an intraperitoneal cannula and feed intake was monitored for 12 h post-injection using a self-feeder system. Cck and Grp decreased feed intake in a dose-dependent manner, hormone-specific both in terms of magnitude and duration. Cck had an immediate inhibitory effect on feed intake, which lasted two-three hours, whereas the immediate inhibitory effect of Grp lasted for the entire 12-hour observation period. The data suggest that Cck acts as a short-term satiety signal in rainbow trout, while Grp acts as a longer-term appetite suppressor.