PURGING TIME ON MUSCLE QUALITY AND NUTRITIONAL VALUE OF YELLOW CATFISH (PELTEOBAGRUS FULVIDRACO) UNDER OPEN FLOWING WATER MODE

This experiment was conducted to investigate the effect of purging time on muscle quality and nutritional value of yellow catfish (Pelteobagrus fulvidraco) under open flowing water mode. Yellow catfish of (15.69±2.28) g at the rapid growth stage were randomly divided into 4 groups with 3 replicates in each group. The yellow catfish were temporarily fed for 0 (control), 20d, 30d and 40d respectively. During the experiment, Pelteobagrus fulvidraco were fed with a compound diet, and the water quality was regularly measured during the breeding process. After the experiment, the growth performance and serum biochemical indexes were measured; the composition of amino acids, fatty acids and textural properties in muscle were compared. The results showed as follows: 1) During the purging time period, the content of ammonia nitrogen in the water of the test tank was between 0.03—0.05 mg/L, the content of nitrite nitrogen was 0.01 mg/L, and the dissolved oxygen level exceeded 9.0 mg/L. 2) With the extension of purging time, the final body weight (W_t) and weight gain rate (WGR) of yellow catfish showed an increasing trend, while the specific growth rate (SGR) showed a decreasing trend, with significant differences among groups (P<0.05). There were no significant differences in survival rate (SR), condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) of purging time groups for 20d, 30d and 40d (P>0.05). 3) The contents of albumin (ALB) and total protein (TP) in serum of purging time 30d and 40d group were significantly higher than those of control group and purging time of 20d group (P<0.05), but the activities of gamma-glutamyltransferase (γ-GGT), alkaline phosphatase (ALP), the contents of total cholesterol (TC) and total bile acids (TBA) were significantly lower than those of the control group and the purging time of 20d group; serum total bilirubin (TBIL) content and aspartate aminotransferase (AST) activity in the control group, the purging time of 20d and 30d groups were significantly higher than those of the purging time group for 40d (P<0.05). The content of serum creatinine (CRE) and urine creatinine ratio (UCR) ofPelteobagrus fulvidraco in the purging time groups for 30d and 40d were significantly lower than those in the control group and the purging time for 20d group (P<0.05). 4) The crude protein content in muscle of purging time groups for 30d and 40d was significantly higher than that of control group and purging time group for 20d (P<0.05), but the crude lipid content was significantly lower than that of control group and purging time group for 20d (P<0.05). 5) The total amount of amino acids (ΣAA), total essential amino acids (ΣEAA), total non-essential amino acids (ΣNEAA), total umami amino acids (ΣDAA) and essential amino acid index (EAAI) in the 30d and 40d purging time groups were significantly higher than those in the control group and the 20d purging time group (P<0.05). The first limiting amino acid in muscle of four groups was all phenylalanine+tyrosine. 6) The contents of C20:5n-3+C22:6n-3 (EPA+DHA), monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) in muscle of yellow catfish in purging time group for 40d were significantly higher than those in other groups (P<0.05). 7) The muscle hardness and gumminess properties of purging time group for 40d was significantly higher than those in other groups (P<0.05), and the muscle springiness, chewiness and resilience were significantly higher than those of control group and purging time group for 20d (P<0.05). In this experiment, under the conditions of temporary cultivation, purging time for 40d can improve the muscle quality and nutritional value of yellow catfish, increase the contents of amino acids and fatty acids, reduce the earthen smell of pond cultured fish, and increase the aquaculture benefit ofPelteobagrus fulvidraco.