Ngoh, Si Yan, Shen, Xueyan, Chan, Tai Lok, Nankervis, Leo, and Hua, Katheline (2025) Effects of digestible protein and energy on growth, amino acid requirements and protein utilisation in juvenile Malabar snapper (Lutjanus malabaricus): A four-protein by three-energy factorial design study. Aquaculture, 600. 742200.

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Abstract

The Malabar snapper (Lutjanus malabaricus) is a commercially valuable marine fish widely farmed in the Indo-Pacific region. To address the lack of nutritional information for this species, a factorial design with 12 diets comprising four protein levels (P540, P480, P420 and P360) and three energy levels (Low, Mid and High) was used to evaluate the effects of digestible protein (DP) and digestible energy (DE) on growth, protein retention and utilisation efficiency in juvenile Malabar snapper with an initial size of 39.0 ± 0.34 g. Fish were fed to apparent satiation for 56 days and gained an average body weight ranging from 13.6 g to 34.1 g. Optimal growth of up to 73.1 g was achieved with a dietary DP level of 479.1 g kg⁻¹ at a DP/DE ratio of 25.78 g MJ⁻¹. However, the optimal protein deposition could not be estimated from the range of DP levels investigated. This indicated that a higher dietary DP, above 518 g kg⁻¹, is required for optimal protein deposition. An indirect approach was used to estimate dietary amino acid (AA) requirements in conjunction with the estimation of protein requirements. This indirect method is useful for suggesting EAA levels to be included in an actual dose-response trial. High carbohydrate, low protein diets resulted in reduced feed intake, growth performance, protein retention and utilisation. Growth was optimised with digestible carbohydrates close to the minimum level tested, at 185.8 g kg⁻¹, indicating that either high carbohydrate inclusion limits growth or protein promotes growth. Increased dietary digestible fat led to greater whole-body fat deposition. Still, it did not improve growth rate or protein retention efficiency, indicating no apparent protein-sparing effect from non-protein energy sources. These results highlight the Malabar snapper's high digestible protein requirement and its lack of growth or efficiency benefits from dietary carbohydrates or lipids. The practical implications of these findings are significant, as they provide essential baseline knowledge for formulating appropriate feeds for this species, thereby enhancing the efficiency and sustainability of Malabar snapper aquaculture.

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