Using unessential sulfur amino acids to overcome methionine deficient diets on rice field eel (Monopterus albus)

An eight-week feeding trial was conducted using sulfur amino acids to overcome methionine deficient diets on rice field eel Monopterus albus (initial weight 25.12 ± 0.51 g). Six isonitrogenous and isoenergetic experimental formulations included 55% fish meal group (FM, a reference), 22% fish meal group (D₀), and the rest four diets (22% fish meal) supplemented with 2 g/kg of taurine (DTₐᵤ), methionine (DMₑₜ), cysteamine hydrochloride (DCₛₕ) and cystine (DCyₛ), respectively. Compared with FM, the growth performance of M. albus was markedly declined in D₀ (P < 0.05); while the growth performance of M. albus in DMₑₜ, DCₛₕ and DCyₛ were remarkably higher than D₀ (P < 0.05), and these groups were indifference with FM (P > 0.05). Compared with FM, the highest amount of hepatic vacuoles was observed in D₀, while the proportions of vacuoles were lower in DMₑₜ, DCₛₕ and DCyₛ groups than that in D₀, dietary sulfur amino acids also have improved hepatic transaminase and the ability of amino acid metabolism. Compared with FM, muscular texture, density and diameters of muscle fibres were significantly decreased in D₀ (P < 0.05); while muscular texture were significantly increased in DCₛₕ and DCyₛ (P < 0.05). Compared with D₀, dietary sulfur amino acids improved diameters of the muscle fibres. Myocyte myogenic regulatory (Mrf4, MyoD2, Myog and Mrf4) and myocyte enhancer factors (MEF2b and MEF2c) mRNA expression in D₀ were markedly lower than that in FM (P < 0.05), compared with D₀, the expression of Mrf4 and MEF2b in DMₑₜ were significantly up regulated (P < 0.05); the expressions of Mrf4, MyoD2 and MEF2b in DCₛₕ were markedly higher than that in D₀ (P < 0.05), MyoD2, Myog, MEF2b and MEF2c in DCyₛ also were remarkably higher than that in D₀ (P < 0.05). Overall, our study indicated that dietary methionine, taurine, cysteamine hydrochloride and cystine in low fish meal diet could improve amino acids metabolism and muscle growth for M. albus, moreover, cysteamine hydrochloride and cystine overcame methionine deprivation partly.