Characterization of the digestive enzymes of juvenile Dormitator latifrons (Richardson, 1844)

The Pacific fat sleeper, Dormitator latifrons, is an omnivorous freshwater fish that primarily feeds on detritus. Our understanding of the digestive physiology of this species still needs to be completed, particularly concerning the characterization of its digestive enzymes. This information is crucial in guiding the design of diets that promote optimal digestion of this species, which has the potential for aquaculture. Thus, this study aimed to optimize enzymatic methods and characterize the digestive enzymes of the digestive tract regions: anterior region (AR), middle region (MR), posterior region (PR), and hepatopancreas (HP). Total acid protease, total alkaline protease, amylase, and lipase activities were measured. The enzymatic methods were optimized at an eco-physiological temperature of 25 °C based on extract volume, extract dilution, incubation time, pH, and CaCl₂ concentration to determine specific activity (U/mg of protein). The optimal pH for acid protease (AR) was pH 2.0; while for alkaline protease, the optimal pH was between 7.5 and 11.0. For AR, chymotrypsin was pH 7.0; for the remaining digestive regions, it was pH 9.0-11.0. The optimal pH for amylase was 6.0 to 7.5 (all regions), and for lipase, it was between 7.0 and 11.0, with two apparent in vitro activity peaks (PR). HP experimental samples showed low or no chymotrypsin, amylase, and lipase activity. CaCl₂ did not affect enzyme activity except for amylase and lipase (only in PR and HP, respectively). The acid proteolytic activity (pH 2.0) found in AR and the proteolytic inhibition by pepstatin suggest the presence of a stomach.