This study evaluated growth, body composition, antioxidant capacity, innate immunity and ammonia excretion of European grayling (Thymallus thymallus) fed diets containing different protein and lipid contents. Six diets were produced to contain 30, 40 or 50% protein and 10 or 20% lipid. Juvenile fish averaging 25.2 ± 0.28 g were stocked into eighteen 450-L circular tanks in a recirculating aquaculture system (RAS) and fed the test diets to satiation twice daily for 12 weeks. Fish weight gain (WG) was enhanced (P ˂ 0.05) as dietary protein increased from 30% (229% WG) to 40% (262% WG) and plateaued thereafter. Enhancing protein and lipid content of diet led to reduced feed intake. Also, feed efficiency was improved by increasing dietary protein (by 40.8%) and lipid (by 16.5%) levels. An interaction of protein and lipid was found on whole-body lipid, and muscle lipid content increased as dietary lipid level increased. Muscle arachidonic acid (ARA), eicosapentaenoic acid (EPA, 20:5n-3) and total n-6 long-chain polyunsaturated fatty acids (LC-PUFA) contents enhanced by increasing dietary protein level. Moreover, increasing fat content of diet led to enhanced muscle linoleic acid, linolenic acid, total monounsaturated fatty acids (MUFA), total n-6, ratio of docosahexaenoic acid (DHA, 22:6n-3) to EPA and n-6/n-3. However, EPA, DHA, total n-6 LC-PUFA, total n-3, total n-3 LC-PUFA and EPA/ARA ratio decreased at higher dietary lipid level. Serum triglyceride (TG) level and lactate dehydrogenase (LDH) activity decreased as dietary protein level increased. Increasing fat content of diet led to enhanced serum TG, CHO and glucose concentrations and reduced alanine aminotransferase, aspartate amino transferase and LDH activities. Serum malondialdehyde concentration was enhanced by increasing both dietary protein and lipid. Furthermore, serum myeloperoxidase activity was enhanced at higher dietary lipid level. Water ammonium nitrogen (NH4+-N) concentration was measured after 5 and 24 h of last feeding, and the results indicated the reduction of ammonia excretion as dietary lipid content increased. These findings suggest that 40% dietary protein can support optimal growth of juvenile European grayling reared in RAS and increasing lipid content from 10 to 20% can improve feed utilization and reduce ammonia excretion to the rearing water.

中文翻译：

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膳食蛋白质和脂质水平对欧洲茴鱼 (Thymallus thymallus) 生长、身体成分、血液生化、抗氧化能力和氨排泄的影响

该研究评估了饲喂含有不同蛋白质和脂质含量的饮食的欧洲鳟鱼 (Thymallus thymallus) 的生长、身体成分、抗氧化能力、先天免疫和氨排泄。生产了六种日粮，分别含有 30%、40% 或 50% 的蛋白质和 10% 或 20% 的脂质。将平均 25.2 ± 0.28 克的幼鱼放入循环水产养殖系统 (RAS) 中的 18 个 450 升圆形水箱中，并在 12 周内每天两次喂食试验饲料至饱。随着日粮蛋白质从 30% (229% WG) 增加到 40% (262% WG) 并在此后趋于稳定，鱼的增重 (WG) 增加（P ˂ 0.05）。提高日粮的蛋白质和脂质含量会导致采食量减少。此外，饲料效率通过增加日粮蛋白质（增加 40.8%）和脂质（增加 16.5%）水平而提高。在全身脂质上发现了蛋白质和脂质的相互作用，和肌肉脂质含量随着膳食脂质水平的增加而增加。通过增加膳食蛋白质水平，肌肉花生四烯酸 (ARA)、二十碳五烯酸 (EPA, 20:5n-3) 和总 n-6 长链多不饱和脂肪酸 (LC-PUFA) 含量增加。此外，增加饮食中的脂肪含量导致肌肉亚油酸、亚麻酸、总单不饱和脂肪酸 (MUFA)、总 n-6、二十二碳六烯酸 (DHA, 22:6n-3) 与 EPA 和 n-6/ n-3。然而，EPA、DHA、总n-6 LC-PUFA、总n-3、总n-3 LC-PUFA和EPA/ARA比率在较高的膳食脂质水平下降低。随着膳食蛋白质水平的增加，血清甘油三酯 (TG) 水平和乳酸脱氢酶 (LDH) 活性降低。饮食中脂肪含量的增加导致血清TG、CHO和葡萄糖浓度升高，丙氨酸转氨酶降低，天冬氨酸氨基转移酶和 LDH 活性。通过增加膳食蛋白质和脂质来提高血清丙二醛浓度。此外，血清髓过氧化物酶活性在较高的膳食脂质水平下增强。在最后一次饲喂 5 小时和 24 小时后测量水氨氮 (NH4+-N) 浓度，结果表明，随着日粮脂质含量的增加，氨排泄量减少。这些发现表明，40% 的日粮蛋白质可以支持在 RAS 中饲养的欧洲鳟鱼幼鱼的最佳生长，将脂质含量从 10% 增加到 20% 可以提高饲料利用率并减少氨向养殖水中的排泄。血清髓过氧化物酶活性在较高的膳食脂质水平下增强。在最后一次饲喂 5 小时和 24 小时后测量水氨氮 (NH4+-N) 浓度，结果表明，随着日粮脂质含量的增加，氨排泄量减少。这些发现表明，40% 的日粮蛋白质可以支持在 RAS 中饲养的欧洲鳟鱼幼鱼的最佳生长，将脂质含量从 10% 增加到 20% 可以提高饲料利用率并减少氨向养殖水中的排泄。血清髓过氧化物酶活性在较高的膳食脂质水平下增强。在最后一次饲喂 5 小时和 24 小时后测量水氨氮 (NH4+-N) 浓度，结果表明，随着日粮脂质含量的增加，氨排泄量减少。这些发现表明，40% 的日粮蛋白质可以支持在 RAS 中饲养的欧洲鳟鱼幼鱼的最佳生长，将脂质含量从 10% 增加到 20% 可以提高饲料利用率并减少氨向养殖水中的排泄。