Methionine (Met) is one of the most limiting essential amino acids in aquafeeds, and different commercial feed-grade Met sources are available for diet supplementation, namely L-Met, DL-Met, and hydroxy-Met (OH-Met). In this work, we compared the bioefficacy of OH-Met and DL-Met as diet supplements for gilthead seabream (Sparus aurata) juveniles reared at normal (22°C) and high (29°C) water temperatures. Two isoproteic (50%) and isolipidic (20%) practical diets (24% fish meal; 6% fish oil) were formulated to contain 1% Met and were supplemented with 0.2% DL-Met (diet DL-Met) or OH-Met (diet OH-Met). The diets were fed to triplicate groups of fish with an initial body weight of 13 g for 78 days. Growth performance and N retention (%) were higher at 29°C. However, feed efficiency, protein efficiency ratio, and hepatic and visceral indexes were higher at 22°C. Hepatic oxidative stress indicators were not affected by dietary Met source. In the muscle, however, oxidative stress index and lipid peroxidation were lower in fish fed the OH-Met diets. Overall, DL-Met and OH-Met proved to be similarly effective as dietary methionine sources for gilthead seabream, while OH-Met seemed to be more effective in reducing oxidative stress in fish reared at high temperatures.

中文翻译：

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膳食蛋氨酸来源对高温饲养金头鲷幼鱼生长性能和抗氧化潜力的评价

蛋氨酸 (Met) 是水产饲料中最受限制的必需氨基酸之一，不同的商业饲料级 Met 来源可用于日粮补充剂，即 L-Met、DL-Met 和羟基蛋氨酸 (OH-Met)。在这项工作中，我们比较了 OH-Met 和 DL-Met 作为在正常（22°C）和高（29°C）水温下饲养的金头鲷（Sparus aurata ）幼鱼的饮食补充剂的生物功效。两种同蛋白 (50%) 和异脂类 (20%) 实用日粮（24% 鱼粉；6% 鱼油）配制为含有 1% Met，并补充 0.2% DL-Met（日粮 DL-Met）或 OH- Met（饮食 OH-Met）。将这些饲料喂给初始体重为 13 克的三组鱼，持续 78 天。 29°C 时的生长性能和氮保留率 (%) 较高。然而，饲料效率、蛋白质效率、肝内脏指数在22℃时较高。肝脏氧化应激指标不受膳食蛋氨酸来源的影响。然而，在肌肉中，喂食 OH-Met 饲料的鱼的氧化应激指数和脂质过氧化程度较低。总体而言，DL-Met 和 OH-Met 被证明作为金头鲷的膳食蛋氨酸来源同样有效，而 OH-Met 似乎在减少高温饲养的鱼的氧化应激方面更有效。