Table_11_Exploring the Impact of a Low-Protein High-Carbohydrate Diet in Mature Broodstock of a Glucose-Intolerant Teleost, the Rainbow Trout.DOCX

Sustainable aquaculture production requires a greater reduction in the use of marine-derived ingredients, and one of the most promising solutions today is the augmentation in the proportion of digestible carbohydrates in aquafeed. This challenge is particularly difficult for high trophic level teleost fish as they are considered to be glucose-intolerant (growth delay and persistent postprandial hyperglycemia observed in juveniles fed a diet containing more than 20% of carbohydrates). It was previously suggested that broodstock could potentially use carbohydrates more efficiently than juveniles, probably due to important metabolic changes that occur during gametogenesis. To investigate this hypothesis, 2-year old male and female rainbow trout (Oncorhynchus mykiss) were either fed a diet containing no carbohydrates (NC) or a 35%-carbohydrate diet (HC) for an entire reproductive cycle. Zootechnical parameters as well as the activities of enzymes involved in carbohydrate metabolism were measured in livers and gonads. Fish were then reproduced to investigate the effects of such a diet on reproductive performance. Broodstock consumed the HC diet, and in contrast to what is commonly observed in juveniles, they were able to grow normally and they did not display postprandial hyperglycemia. The modulation of their hepatic metabolism, with an augmentation of the glycogenesis, the pentose phosphate pathway and a possible better regulation of gluconeogenesis, may explain their improved ability to use dietary carbohydrates. Although the HC diet did induce precocious maturation, the reproductive performance of fish was not affected, confirming that broodstock are able to reproduce when fed a low-protein high-carbohydrate diet. In conclusion, this exploratory work has shown that broodstock are able to use a diet containing digestible carbohydrates as high as 35% and can then grow and reproduce normally over an entire reproductive cycle for females and at least at the beginning of the cycle for males. These results are highly promising and suggest that dietary carbohydrates can at least partially replace proteins in broodstock aquafeed.

可持续水产养殖生产亟需大幅减少海洋源性原料的使用，而当前最具潜力的解决方案之一，便是提升水产饲料中可消化碳水化合物的占比。对于高营养级硬骨鱼而言，这一挑战尤为艰巨：这类鱼类被普遍认为存在葡萄糖不耐受（glucose-intolerant）现象——饲喂碳水化合物占比超过20%的饲料时，其幼鱼会出现生长迟缓以及持续性餐后高血糖（postprandial hyperglycemia）。此前有研究提出，亲鱼对碳水化合物的利用效率可能优于幼鱼，这或许与配子发生（gametogenesis）过程中发生的重要代谢变化有关。为验证这一假说，本研究选取2年龄的雄性和雌性虹鳟（Oncorhynchus mykiss），在完整生殖周期内分别饲喂无碳水化合物饲料（no carbohydrates, NC）与35%碳水化合物饲料（35%-carbohydrate diet, HC）。研究人员检测了肝脏与性腺中的养殖性能参数，以及参与碳水化合物代谢的酶活性。随后通过繁殖实验，探究该饲料对鱼类繁殖性能的影响。亲鱼可正常采食HC饲料，且与幼鱼的常见表现相反，它们能够正常生长，未出现餐后高血糖现象。其肝脏代谢的调控变化——包括糖原合成（glycogenesis）、磷酸戊糖途径（pentose phosphate pathway）的增强，以及糖异生（gluconeogenesis）的可能更佳调控——或可解释其对膳食碳水化合物利用能力的提升。尽管HC饲料确实会诱导早熟成熟（precocious maturation），但鱼类的繁殖性能并未受到影响，这证实亲鱼在饲喂低蛋白高碳水化合物饲料（low-protein high-carbohydrate diet）时仍可正常繁殖。综上，本探索性研究表明，亲鱼能够耐受碳水化合物占比高达35%的饲料，且雌性亲鱼可在完整生殖周期内正常生长与繁殖，雄性亲鱼至少可在生殖周期初期完成正常繁殖。上述结果极具应用前景，提示膳食碳水化合物可在水产亲鱼饲料中部分替代蛋白质。