Inclusion of citric acid and/or amino acid-chelated trace elements in alternate plant protein source diets affects growth and excretion of nitrogen and phosphorus in red sea bream Pagrus major

Nutrient dense diets not only challenge the physiological capabilities of fish but also result in discharge of excess amounts into the environment, causing eutrophication of the receiving water. This study investigated the effect of dietary levels of citric acid (CA) and/or amino acid-chelated trace element (AA-CTE) on growth and nutrient retention in red sea bream and loading of phosphorus (P) and nitrogen (N). Six practical diets were formulated, the control being a fish meal-based diet (F0) without addition of P, CA and AA-CTE. Diet F1 was supplemented with 1% mono calcium phosphate (0.25% P). In diets C1 and C2 fishmeal was replaced with alternate plant protein ingredients and supplemented with 1% and 2% CA, respectively. Diets A1 and A2 were akin to diets C1 and C2, respectively but contained AA-CTE instead of the inorganic trace element. Fish weighing around 12 g were offered the respective diets to satiation during the 12-week trial. Growth and feed performance were lowest for fish fed F0 diet, but significant improvement (P < 0.05) was noticed among those fed diets supplemented with P, CA or AA-CTE. The F1 group had the best growth (final body weight 85.02 g) while A1 group had the best FCR (1). Absorption of P was significantly higher (P < 0.01) for fish that received CA and/or AA-CTE (C1, C2, A1 and A2) compared to group that did not receive them (F0 and F1). The P and nitrogen (N) retention values in fish fed diets with CA and/or AA-CTE were significantly (P < 0.01) greater compared to the rest and this facilitated a reduction in excretion rates. The diet supplemented with 1% CA to an alternate plant protein sources diet without inorganic P supplementation had better performance compared to the diets supplemented with 2% CA, 1% CA + AA-CTE, and 2% CA + AA-CTE. Thus, without addition of inorganic P, 1% CA supplementation to alternate plant protein sources diets significantly improved fish growth, FCR and nutrient retention, besides lowering N and P loading. An efficient level of CA is suggested to be 1% or less in alternative plant protein source diets (containing 35% fish meal). These findings would contribute to the pursuit of environment-friendly feed for red sea bream.