The effects of dietary protein levels with amino acid supplementation on the growth performance, haematological profile and histology of meagre (Argyrosomus regius) in two different size classes

A 12-week feeding trial was conducted to estimate the effects of supplemented amino acids (lysine and methionine) with different dietary protein levels on growth, haematology and liver histology in meagre (Argyrosomus regius) at two different sizes: fingerling (15.2 g) and juvenile (44.4 g). Six practical diets were prepared, and three of these practical diets were formulated with 40 (P40), 44 (P44) and 48% (P48) crude protein without supplementation of amino acids. Other three diets having same protein levels were supplemented with lysine and methionine (P40AA, P44AA and P48AA) to bring these amino acids level up to that estimated to be at the least in the 48% protein diet. Final mean weight (FMW) and specific growth rate (SGR) of P48AA in fingerlings were higher than that of 40AA. According to FMW and SGR of juveniles, there was interaction found between dietary protein levels and the supplementation of amino acids. The FMW and SGR of meagre fed P44AA were higher than that of fish fed the other diets, except fish fed the P48. Economic profit index, packed cell volume and haemoglobin for juvenile meagre were significantly improved with the dietary protein level and amino acid supplementation. The liver tissues of the P48 group in both sizes displayed better structure compared with the other groups. In conclusion, dietary crude protein content of practical diets for juvenile meagre could be reduced from 48% to 44% by adding essential amino acids with an enhancement in growth, health and economic profit.