One-year old European perch (Perca fluviatilis)-specific in vitro digestion studies in special regard to feed optimization

The aim was to investigate the effect of water temperature on digestive enzyme activities of perch, to determine at which temperature their digestion process is more suitable. European perch (Perca fluviatilis) (1 year old, 50–60 g, 10 cm) were kept in recirculation system with the stocking density of 9 kg/m3 in 150 litre-sized-tanks, at 16°C, 18°C, 20°C, 22°C. Fish were kept for 1 week acclimatization, starved for 72 hours before feeding (crude protein: 45 %, crude fat: 16 %, crude fiber: 2.6 %; digestible energy: 18.5 MJ). Feeding was twice, with a 6 hours interval. There were 3 tanks for each proper temperature treatment; every tank contained 100 fish. 10 fish were moved out from all the tanks (30 fish per treatments). Stomach, intestine of fish was separated and their walls were washed with 1 ml of distilled water (pH 2.5), with 1 ml of 50 mM Tris-HCl, containing 0.5 M NaCl, 20 mM CaCl2 (pH 7.8), respectively, to retrieve gastric and intestinal digestive extracts. Extracts were used for pepsin, trypsin. total alkaline proteolytic, lipase, α-amylase activity tests. We have succeeded in developing protocol for gaining enzyme-containing extracts to monitor the realistic physiological conditions of perch based on enzyme activity measurements. The protocol was considered to be easy to implement and to provide sufficient enzyme extract to simulate subsequent in vitro digestion. The ambient temperature affected enzyme activities significantly: pepsin (40480.14; 69245.91; 79305.86; 40236.32 U/mg protein), trypsin – (7.77; 9.88; 11.12; 5.42 U/mg protein), total alkaline proteolytic - (1.47; 1.14; 1.25; 0.84 U/mg protein), lipase – (0.40; 1.16; 0.72; 0.76 U/mg protein) and α-amylase (0.29; 0.395; 0.98; 1.17 U/mg protein) activities, respectively at 16, 18, 20 and 22°C. Based on protease activities, 18–20°C was chosen to be the most appropriate rearing temperature, which contributes the most to the proper growth of the fish. •Simple-to-implement protocol for yielding digestive enzyme extracts of Perca fluviatilis was successfully developed.•The purity of enzyme extracts was checked and found to be adequate for measuring enzyme activities.•Study gave suggestion to standardize enzyme-activity measurement protocol for fish digestive enzymes.•Novel results on perch-specific enzyme activities can be used for perch-specific in vitro digestion simulation.•Based on all enzyme activities, the most effective temperature for digestion and rearing of European perch was 18–20