Study of digestive enzyme activities in rainbow trout (Oncorhynchus mykiss) over feed deprivation and refeeding periods

Digestive enzymes have the pivotal role in the nutrient uptake and growth of fishes. However, information about the behavior of digestive enzymes and their restoring potential during different deprivation and refeeding periods is scarce. In this study we evaluated whether rainbow trout with an average body weight of 44.01 g ±0.19 ±S.E. could regulate and rehabilitate its digestive capacity after different feed deprivation periods. The study lasted for eight weeks. Four treatments with three replicates including a control group without food deprivation and treatment 1, 2 and 3 with 1, 2 and 3 week(s) of food deprivation, respectively, were set up. Then, fish were fed ad lib for five weeks from the onset of week four up to the end of week eight, twice daily under photoperiod of 15L:9D and temperature of 17.4±0.1°C. Specific enzyme activities of trypsin, chymotrypsin and lipase were measured on days 21 (before commencement of feeding), 33, 43 and 55 (the end of the experiment). At the end of deprivation period the control group had significantly higher (p<0.05) trypsin activity (95.4±12.2) compared to treatments 1 (78.1±5.1), 2 (75.2±10.1) and 3 (85.4±9.3). Starved treatments showed no chymotrypsin activity at the end of starvation period as compared to the control group which showed the enzyme activity of 44.77±9.4. Lipase activity of the control group (37.7±2.3) was significantly higher (p<0.05) than those of treatments 1 (23.0±2.4), 2 (22.1±2.2) and 3 (27.3±5.0) on day 21. However, upon elongation of the feeding period up to day 55, the enzyme activity levels were restored to the level of control group (p>0.05). The results clearly indicated that food intake is one of the main mediatory factors to regulate digestive enzyme activities and fish can restore its digestive capacity following different deprivation periods.