Evaluation of Dietary Methionine Sources on Growth Performance and Antioxidant Potential of Gilthead Seabream Juveniles Reared at High Water Temperature

Abstract 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.