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Aims: Due to vital role of optimum feeding rate on success and profitability of an aquaculture practice, feeding rates were examined in different life stages of Beluga sturgeon.
Methods: Feeding rates were 5%, 7%, 9%, 11%, 13% and 15% in stage 1; 2%, 4%, 6%, 8%, 10% and 12% in stage 2; 1.5%, 2%, 2.5%, 3% and 3.5% in stage 3; 1.5%, 1.75%, 2%, 2.25% and 2.5% in stage 4. Farming durations of stages 1 to 4 were 10, 10, 42 and 56 days, as well as initial mean weights were 1.85, 7, 112.04 and 300.54 g, respectively.
Findings: Results showed that optimum feeding rates from growth and feeding parameters point of view were 9% and 5%, respectively, in stage 1. In stage 2 also optimum feeding rates were different from growth and feeding point of view, as they were 4% and 2%, respectively. For both aspects of growth and feeding parameters, optimum feeding rate was 2.5% of body weight in stage 3. In stage 4, the lowest food conversion rate was observed in the feeding rate of 1.5% and there were no significant differences between treatments from growth parameters point of view.
Conclusion: Growth and feeding parameters were affected with feeding rates in stages 1, 2 and 3. In stage 4, feeding rates influenced feeding parameters, but had no significant effects on growth performance.
 

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This study evaluated the interactive impacts of water temperature and feeding rate on digestive enzymes, intestine histology, growth and stress-related genes, and cultivable intestinal microbiota of Asian seabass (Lates calcarifer). For this purpose, 180 fish (85.0±3.0 g) were reared at three different temperatures (20, 27, and 33°C) and two feeding rates (apparent satiation and 2.5% of biomass) with three replications for 6 weeks. The results revealed no significant differences among different treatments regarding the activity of digestive enzymes (P˃ 0.05) of fish reared under different temperatures and feeding rates. The length, width, and thickness of intestinal villi were unaffected by different temperatures and feeding rates (P˃ 0.05). In addition, no variations were found in the total aerobic bacterial count of fish gut from different experimental groups (P˃ 0.05). At the molecular level, IGF-I and HSP70 coding genes were found to be highly expressed in experimental treatments (P< 0.05). To conclude, the present study showed that temperatures between 27 to 33°C were more optimal for Asian seabass, and the different temperatures and feeding rates did not affect the digestive enzymes, intestine histology, and gut microbiota of juvenile Asian seabass after 6 weeks.