Muscle nutrient composition of Coilia nasus in brackish water and fresh water cultured modes

In order to understand the effect of brackish water and fresh water culture modes on the nutrient accumulation of Coilia nasus cultured in pond, the muscle nutritional composition and quality of Coilia nasus ecologically cultured in brackish water (salinity 10-15) and freshwater (0.4-1.0) model were investigated and analyzed by biochemical analysis methods. The results show that the muscle crude fat content (7.27 %) of C. nasus cultured in brackish water mode was significantly higher than that of freshwater mode (4.30 %), while the muscle moisture (72.54 %) and crude ash content (1.32 %) of brackish water mode were significantly lower than that of freshwater mode (76.85 % and 2.06 %, respectively), No significant difference in the crude protein content of muscle was found between two cultural modes. Except that no significant difference in tryptophan and cystine was found between the two cultural modes, the contents of other 16 amino acids of brackish water mode were significantly lower than those of fresh water mode; the total amino acid (TAA), total essential amino acid (EAA), total half-essential amino acid (HEAA), total non-essential amino acid (NEAA), and total delicious amino acid (DAA) contents of brackish water mode were significantly lower than those of fresh water mode, and there was no significant difference in the EAA/TAA and EAA/NEAA specific values of C. nasus muscle between two cultural modes, while the DAA/TAA specific value(40.32) of brackish water mode were significantly lower than that of fresh water mode (40.68). The essential amino acid index (EAAI) (58.59) of brackish water mode was lower than that of fresh water model (72.04), while the specific value of branched amino acids to aromatic amino acids (F value) (2.44) of brackish water mode was higher than that of fresh water mode (2.35). In the 28 kinds of fatty acids detected, there was no significant difference in the contents of 11 kinds of fatty acid between two cultural modes. In major fatty acids, C16:0, C18:0, C18:1n9c, C22:5n3 (DPA) and C22:6n3 (DHA) contents of brackish water group were significantly higher than that of fresh water group, while the C18:2n6c and C18:3n3 contents of brackish water mode were significantly lower than those of fresh water mode. SFA, MUFA and EPA+DHA contents of brackish water mode were significantly higher than those of fresh water mode; ∑n3PUFA/∑n6PUFA (3.93) of brackish water mode was significantly higher than that of fresh water model (2.10), this is consistent with the fact that n3PUFA/n6PUFAs of migratory fish muscle is higher in seawater and lower in freshwater. Therefore, the muscle protein of C. nasus cultured in fresh water is more nutritious and delicious, while brackish water culture is beneficial to the accumulation of fat and the retention of the MUFA (especially C18:1n9c) in C. nasus. The osmotic pressure of brackish water may be near the isotonic point of C. nasus, and this is more conducive to the accumulation of nutrients and the growth of C. nasus. It is suggested that brackish water should be used in the commercial fish culture stage of C. nasus and fresh water should be used in the intensive culture stage of C. nasus before the sales.