Optimal levels of methionine and the impact of water leaching in juvenile Penaeus vannamei diets

Abstract

An 8-week feeding trial was conducted to determine the optimal levels of dietary methionine (Met) for juvenile Pacific whiteleg shrimp, Penaeus vannamei, while evaluating the effects of amino acid (AA) leaching. Six practical diets were formulated to be isonitrogenous and isolipidic, with total Met levels ranging from 0.51 % to 1.37 % in 0.14–0.21 % increments, and total sulfur AA (Met + Cysteine) levels from 0.88 % to 1.75 % on a dry matter basis (DM). The total nitrogen content was balanced across all diets by replacing Met with a non-essential AA mixture. Each diet was randomly assigned to seven replicate groups of 15 juvenile shrimp with an initial body weight (BW) of 0.80 ± 0.05 g. Shrimp were fed six times daily until apparent satiation. The effects of varying dietary Met levels on survival, growth performance, feed utilization, and muscle tissue composition were evaluated, with Met leaching rates measured at 30 minutes in full-strength seawater. Results showed consistently high survival rates across all treatments, while final shrimp BW significantly increased with higher Met levels, particularly between diets containing 0.82 % and 0.99 % Met. Met leaching rates positively correlated with synthetic Met supplementation, significantly increasing as total dietary Met concentration rose. Muscle tissue composition analysis highlighted Met's crucial role in protein synthesis and physiological function, revealing significant differences in crude protein and essential AA deposition among dietary treatments. Higher dietary Met promoted optimal protein and AA muscle content up to 0.82 %, after which a saturation effect was observed. In conclusion, this study emphasizes the importance of accounting for nutrient leaching when determining optimal AA levels for juvenile P. vannamei. Quadratic regression analysis indicated that an optimal dietary Met level of approximately 1.04 % in the dry diet (2.73 % of dietary protein) was most effective under these experimental conditions. Considering Met leaching rates to more accurately estimate the amount of Met available to shrimp after feed exposure to water, it was established that an optimal level of 0.74 % Met in the dry diet (2.20 % of dietary protein) after 30 minutes of immersion in water optimally supports growth and feed efficiency. This finding refines the actual optimal dietary Met level for juvenile Penaeus vannamei, establishing a new benchmark for future nutritional research in shrimp aquaculture.