Study on flesh quality and physiological response of grass carp cultivated at higher density in-pond raceway system

In-pond raceway systems (IPRS) are a high-density ecological green pond aquaculture mode, which has developed rapidly in China in recent years. This study evaluated the flesh quality and physiological response of grass carp under the IPRS mode. Compared with the traditional earthen pond (EP) mode, the grass carp hepatosomatic index and viscerosomatic index under the IPRS mode are significantly (p < 0.05) lower. And the water holding capacity of grass carp muscles were significantly (p < 0.05) improved. Compared with EP mode, grass carp muscles under the IPRS mode have more crude protein content and less crude fat content, and have higher muscle fiber density and smaller muscle fiber diameter. In the IPRS mode, the total amount of essential amino acids ( n-ary sumation EAA) in grass carp muscle increased significantly (p < 0.05), and the content of savory amino acids increased significantly (p < 0.05). In addition, the content of eicosapentaenoic acid and docosahexaenoic acid in the muscle fatty acids of IPRS grass carp was also significantly (p < 0.05) higher than EP mode. At the same time, in order to cope with the high-density culture mode of IPRS, the activity of catalase and superoxide dismutase in grass carp muscle was significantly (p < 0.05) increased, and the alanine aminotransferase in serum, aspartate aminotransferase, as well as other biochemical indexes, increased significantly (p < 0.05). In the IPRS mode, the mass-specific lamellae respiratory area of the gill increased significantly (p < 0.05), and the volume of the interlaminar cell mass decreased significantly (p < 0.05) to increase oxygen intake. Taken together, our results show that grass carp will produce relevant physiological response to cope with the IPRS high-density culture environment, while their flesh yield, flesh quality, and nutritional value is improved.