Feeding Behaviour and Bioavailability of Essential Amino Acids in Shrimp Penaeus monodon Fed Fresh and Leached Fishmeal and Fishmeal-Free Diets

SIMPLE SUMMARY: While success has been achieved with replacing fishmeal entirely in diets for whiteleg shrimp Litopenaeus vannamei, giant tiger prawn Penaeus monodon still requires fishmeal for optimum culture performance. Crystalline amino acid (CAA) supplementation is becoming popular in shrimp feed formulation and is needed in low fishmeal diets as common alternative protein sources are typically deficient in essential amino acids, such as methionine and lysine. Furthermore, the slow feeding behaviour of shrimp compared to other cultured aquatic species means that feeds can lose specific nutrients before they are consumed. In particular, highly soluble CAA are prone to leaching. In this study, we examined the feeding behaviour, CAA leaching loss and AA uptake in large Penaeus monodon juveniles through a series of short-term experiments using a terrestrial meal-based formulation (TM) enriched with CAA and a traditional fishmeal-based formulation (FM). Feeding behaviour and nutrient bioavailability was found to be similar for the two diets. However, leaching over as little as 60 min had a major impact on AA absorption for the TM diet. The growth implications associated with leaching losses need to be investigated. However, the results indicate the need for careful feeding management as increased reliance on CAA for P. monodon culture could lead to suboptimal nutrition. ABSTRACT: The complete replacement of fishmeal with terrestrial meals did not have a negative impact on the attractiveness, palatability, and apparent digestibility of the formulation. Shrimp were found on average to eat more and have similar appetite revival on the terrestrial meal-based formulation (TM) diet compared to the traditional fishmeal-based formulation (FM) diet. However, methionine (Met) and lysine (Lys) leached out rapidly from the TM diet, and as a result, this initially overfortified diet showed lower levels of those AA in comparison to FM after 60 min immersion. Both dietary Lys and Met were sub-optimal in TM within 120 min of immersion, whereas in comparison, the FM diet supplied consistent levels of EAA for up to 240 min immersion. Nonetheless, shrimp fed fresh TM had significantly higher peak haemolymph concentrations at 30 and 60 min for total AA, Met, and Lys than FM-fed shrimp. The over-supply of CAA far compensated leaching losses, and CAA were well absorbed and used by the shrimp within 120 min, with no obvious signs of asynchronous absorption of CAA to protein-bound AA. However, shrimp fed the TM diet that had leached out for 60 min, had haemolymph concentrations of Met and Lys that were only 41% and 44% of the ones on fresh feed respectively, while there was a negligible effect of leaching on FM. This study provides further insight into the feeding behaviour and bioavailability of dietary amino acids for P. monodon juveniles.