New insights into tambaqui (Colossoma macropomum) feeding behavior and digestive physiology by the self-feeding approach: effects on growth, dial patterns of food digestibility, amylase activity and gastrointestinal transit time

Fish and terrestrial vertebrates usually exhibit daily feeding rhythms that can be associated with daily patterns of digestion dynamics. The classic approach used in feeding studies usually neglects these biological rhythms. Therefore, this study aims to investigate the existence of daily feeding rhythms for tambaqui (Colossoma macropomum), and of daily nutrients and energy digestibility, amylase activity rhythms and gastric evacuation. Four trials were conducted by evaluating: 1) daily feeding rhythms by the self-feeder method; 2) digestibility with two different feeding schedules (midday feeding ML or midnight feeding MD) and assessment of the resulting growth differences; 3) circadian rhythms in amylase activity; 4) the gastric evacuation of the fish fed at the ML or MD. Tambaqui clearly showed nocturnal feeding behavior, with 84.98% of daily food demand occurring at night (p = 0.001). The fish fed at MD grew better than those at ML (p = 0.000), but this result was not followed by improved digestibility (p = 0.500). A clear daily rhythm of amylase activity was observed in fish under both the ML and MD conditions, with an activity peak at night for both groups. Lastly, the tambaqui fed at ML obtained higher intestinal evacuation rates compared to those fed at MD (p = 0.000). Therefore, the results confirm the existence of daily rhythmicity in feeding activity, amylase and evacuation time in tambaqui. Taken together, our results demonstrate that a list of some of tambaquis' digestive physiology and behavioral traits are under circadian control, which should be considered to establish optimized feeding protocols.