Developing sustainable aquaculture remains a challenge, notably finding suitable alternatives to marine ingredients in carnivorous fish diets such as rainbow trout (Oncorhynchus mykiss) in changing climate. These new diets are especially important because rainbow trout are an ecologically and economically significant aquaculture species. Therefore, we investigated the impact of sustainable ingredients and water temperature manipulations on rainbow trout growth characteristics and mitochondrial function. A total of 432 fish were fed four isocaloric, isolipidic, and isonitrogenous diets comprised 40 % crude protein and 20 % lipid and formulated as diet 1 (animal-based protein +25 % fish oil/ 50 % plant oil/ 25 % terrestrial animal oil), or diet 2 (animal-based protein +100 % plant oil), or diet 3 (plant-based protein +25 % fish oil/ 50 % plant oil/25 % terrestrial animal oil), or diet 4 (plant-based protein +100 % plant oil) at 14 °C or 18 °C or 20 °C water temperature. Results showed percent weigh gain (PWG) and specific growth rate (SGR), feed efficiency (FE), and feed intake (FI) were significantly (P < 0.05) higher in fish reared at 14 °C and 18 °C compared to 20 °C. The PWG, FE, FI, and SGR levels were significantly (P < 0.05) higher for fish fed diets 1 and 2 than those fed diets 3 and 4. Dietary composition influenced whole-body proximate composition, while temperature affected protein, moisture, and lipid contents. For protein, lipid, and energy contents, temperature-diet interactions were significant (P < 0.05). There were differences in mitochondrial enzymatic activities in muscle, liver and intestine. Diet affected only complex V activity in the liver, whereas temperature significantly (P < 0.05) affected the activities of complexes II, III, and V. A temperature-dietary interaction was observed for complex V. The temperature regimens, but not dietary composition, affected muscle mitochondrial enzymatic activities. There were significant (P < 0.05) effects of temperature on complex III, IV, and citrate synthase activities in the intestine, whereas dietary composition had no significant impact (P > 0.05). Based on diet, temperature, and diet-temperature interactions effects, selected genes were expressed differently in different tissues. The nd1, cox2, cytb, cox1, atp6 and PPAR-α genes were significantly influenced by diet and temperature interactions in muscle, liver and intestine. Overall, our results showed that both temperature and dietary composition had significant effects on growth characteristics, proximate composition, mitochondrial enzymatic activities, and their interactions on gene expression levels in rainbow trout. These findings underscore the importance of considering these factors in the development of plant-based aquafeeds in order to optimize growth and productivity.
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