Abstract:Large yellow croaker (Larimichthys crocea) fish are a major marine aquaculture product in China. They mainly farmed in nearshore floating cages, but the irrational layout of nearshore aquaculture and high aquaculture density seriously affect the flesh quality. Offshore aquaculture—such as deep-water cages and offshore ships—has the advantages of a wide area and good water quality, resulting in improvement in the quality of large yellow croaker cultured in offshore systems. Nevertheless, instances exist in which large yellow croaker raised in nearshore floating cages may be misrepresented as being cultured in offshore systems, likely motivated by the higher market value associated with offshore cultivation. Therefore, it is necessary to investigate the quality characteristics of large yellow croaker cultured in different modes and screen for representative indices that can be used to distinguish between these different modes. Thus, large (500–550 g) and small (250–330 g) fish reared in deep-water cages, floating cages, and offshore ship systems were collected from October to November 2023. The deep-water and floating cages were fixed in the Sandu Bay, Ningde City, Fujian Province. In the offshore system, fish were cultured in Guoxin 1, which shifted between the Ningde and Qingdao Sea areas. After collection, the morphology, texture, basic nutrients, amino acids, fatty acids, taste profile, and volatile compound odor of the flesh were analyzed. The results showed that: (1) the morphology of large yellow croaker reared offshore was better than that nearshore with lower condition factor and higher body length/height and caudal peduncle length/height. The condition factor and body length/height ratio of the larger fish were lower than those of the smaller fish in the same culture mode. (2) The hardness, adhesiveness, and stickiness of the fish from offshore ships and deep-water cages were higher than those from floating cages of the same size. For fish from the same culture mode, the hardness, adhesion, and chewiness of the larger fish were higher than that of the smaller fish. The springiness of the smaller fish cultured in floating cages was significantly lower than that of the larger fish. (3) The crude fat content of the larger fish was lower than that of the smaller fish across different farming modes. For the larger fish cultured in floating cages, the crude fat content was significantly higher than that of fish in the other two culture modes and was lowest in the offshore ship system. Fish cultured in the offshore ship system had lower protein levels than those in the other two culture modes. In the same culture mode, the ash content of the smaller fish was lower than that of the larger fish, but the moisture contents were similar. Nutritional evaluation of amino acids suggested that the limiting amino acid of the smaller fish was isoleucine (ILE), while in the larger fish, it was MET and cysteine (CYS). The monounsaturated fatty acid content of the fish reared in offshore ships and deep-water cages was significantly higher than that of fish reared in floating cages. The eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels of the fish were significantly higher in deep-water and offshore ship systems than in floating cages. (4) Inosine monophosphate (IMP) contributes more to the flavor of large yellow croaker, and in the same culture mode, the IMP content of the larger fish was significantly higher than that of the smaller fish. Large yellow croaker reared offshore exhibited higher umami and sweet tastes, whereas those reared in deep-water cages showed higher richness. Large yellow croaker cultured in floating cages had higher levels of 2-methylbutyraldehyde, 2-methylpropionaldehyde, isopropylidene acetone, acetone, 2-hexanone, 2-pentanone, ethyl caproate, and methyl acetate than those cultured in the other two modes, indicating a richer volatile flavor. Isovaleraldehyde, alpha-pinene, ethyl acrylate, 2-butanone, and butanal-D contents were higher in the smaller fish than in the larger fish, indicating a more intense fruity flavor. Orthogonal partial least squares discriminant analysis identified methyl trans-9-octadecenoate, 2-butanol-M, butanal-M, umami, astringent aftertaste, richness, methionine, and cysteine as important indicators for distinguishing large yellow croaker reared under different culture modes. In summary, emerging culture modes such as offshore ships and deep-water cages are important ways to improve the quality of large yellow croaker by improving the body shape, texture, and taste.
