Malabar snapper (Lutjanus malabaricus ) is an economically important marine fish throughout the Indo-Pacific region, commonly farmed in Malaysia and Singapore. Despite its economic importance, the nutritional requirement s of snappers (L. spp. ) are currently sparse and variable, and no species-specific feed is available. This project, comprising four interconnected studies, was conceived to (1) evaluate the energy utilisation efficiencies of digestible macronutrients, (2) determine the digestible protein and energy requirements , (3) assess the nutritional values of ten protein ingredients, including fish meal (FM), and (4) determine the cost-effectiveness of optimised feed formulations.
In Study 1 , juvenile Malabar snapper’s maintenance energy requirement (DEm) was estimated to be 76.7 kJ kg -0.8 d-1. The utilisation efficiencies of digestible protein and fat for growth were estimated to be 73.6% and 68.3%, respectively. A protein-sparing effect from lipids was observed when energy intake levels were below DEm. Above DEm , protein retention efficiency was lower when compared to fat, indicating a high demand for digestible protein to support growth. F indings from S tudy 1 were reaffirmed in Study 2 when t he digestible protein level and digestible protein-to-energy ratio (DP/DE) were estimated to be 511.8 g kg-1 and 25.5 g MJ-1, respectively , for optimum growth and protein deposition. In Study 3, ten alternative protein ingredients (i.e., plant-based proteins, animal by-products and insect meals) were evaluated against a 70% protein FM for their digestibility, nutrient availability and cost-effectiveness. Single-cell protein (SCP) from bacteria meal contained a profile of digestible amino acids most similar to FM , followed by black soldier fly larvae (BSFL) meal. However, the fish fed with SCP diet containing 30% SPC had significantly slower growth and lower feed intake (P < 0.05) than those fed on BSFL diet with the same inclusion rate. This indicates that SCP needs to be dose-optimised or balanced with nutrients other than amino acids for optimal performance. Study 4 compiled the results from Studies 1-3 to develop a series of optimised diets tailored to the essential nutrient requirements of Malabar snapper. Compared to a commercial control diet, the best-performing diets exhibited improved growth performance , feed conversion ratio (FCR) and cost efficiency by at least 50%, 25% and 20%, respectively (Figure 1 ). Although species-specific diets are more expensive, using a nutritionally optimised and cost-effective diet can ultimately reduce overall production costs and enhance the productivity of Malabar snapper aquaculture.