Comparative study on the morphological characteristics, nutritional quality, and tastes of large yellow croaker from five cage culture areas: Relay farming improved fish quality

Abstract

Relay culture of large yellow croaker from Fujian to Zhejiang is a good model for improved fish quality. However, there is a scarcity of information regarding the comprehensive evaluation of quality alterations following relay culture. In the present study, the large yellow croaker from Ningde (ND) was transferred to net cages in Dongtou (DT), Nanji (NJ), Dongji (DJ) and Dacheng (DC) for continued culture. The 15-month-old fish from ND, DJ, DC, DT, and NJ were sampled on-site for a subsequent comparative study on the morphological characteristics, nutritional quality, and tastes. Results showed that the fish from DJ, DC, DT, and NJ had a lower condition factor (CF) and a higher ratio of body length to height (L/H) than those from ND. The fish from DJ, DC, DT, and NJ, at rates of 77.8%, 91.3%, 95.7%, and 100%, exhibited different geometric morphometrics from those from ND using 10 typical landmarks and Morpho J software. Ralay culture also significantly affected the histology and ultrastructure of muscle fibers, as reflected by an increase in the muscle fiber density and decreases in the ratio of fiber area to gap, I band width, and sarcomere length in the relay culture fish compared to the ND fish. The relay culture fish showed low lipid content and high moisture content. Relay culture also significantly affected the levels of some nutritional composition, including deceases in the levels of hydrolyzed glycine, C16:0, C18:1n9c, C18:2n6c, Σn-6 PUFA (polyunsaturated fatty acids), Fe (iron), Mn (manganese), and Co (cobalt), and increases in the levels of C20:5n3 (EPA, eicosapentaenoic acid), C22:6n3 (DHA, docosahexaenoic acid), C18:0, Σn-3/Σn-6 PUFA, Σn-3 PUFA, Al (aluminum), Se (selenium), Na (sodium), and Ca (calcium). The levels of taste substances such as guanosine monophosphate (GMP) and most flavor amino acids sharply declined after relay culture. However, the ratio of taste activity value (TAV) of ΣDAA to ΣBAA (delicious amino acids/bitter amino acids) in the DT and NJ fish was higher than that in the ND fish. Significant negative relationships between market price and quality parameters were found, including CF, crude lipid, C18:1n9c, C18:2n6c, Σn-6 PUFA, Fe, Mn, and TAV of GMP, whereas there were positive relationships between market price and 4 quality parameters such as L/H, moisture, Σn-3/Σn-6 PUFA, and the ratio of TAC of ΣDAA to ΣBAA. In conclusion, relay culture improved large yellow croaker quality by changes in morphological characteristics, nutritional quality, and tastes, which provides a theoretical basis for quality improvement.