COMPOUND CHINESE HERBAL MEDICINE ON FLESH QUALITY OF LARGEMOUTH BASS (MICROPTERUS SALMOIDES) IN THE DIET OF FISH MEAL REPLACED BY CHLORELLA MEAL

The present study aimed to investigate the effect of a compound Chinese herbal medicine on the flesh quality of largemouth bass (Micropterus salmoides) when fish meal was replaced with Chlorella meal in their diet. In the fishmeal diet (FM group) of largemouth bass, Chlorella meal completely replaced the fish meal (CM group). Subsequently, in the CM group, the compound Chinese herbs (Chinese Herbal Medicine Compound, CHMC; tonic) were added at levels of 2%, 4%, and 6%, denoted as CMH2, CMH4, and CMH6 groups, respectively. A total of 225 healthy largemouth bass (mean weight 100.20±0.29 g) were randomly divided into five groups, with triplicates per group and fed with five diets, ensuring isonitrogenous (CP: 52%) and isolipidous (CL: 10%), respectively. The feeding period lasted for 80 days. The results revealed the following: (1) The brightness value (L*) from the lateral skin of largemouth bass in CMH2, CMH4, and CMH6 groups was significantly higher than that of FM and CM groups (P<0.05). Additionally, the yellowness value (b*) from the dorsal muscle of largemouth bass in CMH2, CMH4, and CMH6 groups was significantly higher than that of the CM group (P<0.05). (2) The crude fat of the muscle in CMH2, CMH4, and CMH6 groups was significantly lower than that in the FM and CM groups (P<0.05). However, there was no significant difference in crude protein, moisture, and crude ash of the muscle among these groups (P>0.05). (3) The aroma amino acid content, essential amino acid content, and total amino acid content of the muscle in the CMH6 group were significantly higher compared to the FM and CM groups (P<0.05). Additionally, the C16:1n-7 content of the muscle in the CMH4 group was significantly higher than that of the CM group (P>0.05). (4) There was no significant difference in cohesion, elasticity, and dripping loss of fish muscle in each group (P>0.05). However, the hardness, adhesion, adhesiveness, chewing ability, shear force, and pH of fish muscle increased significantly with the addition of compound Chinese herbal medicine (P<0.05). (5) The diameter of muscle fibers in fish from the CMH4 and CMH6 groups was significantly lower than that in the CM group (P<0.05). Additionally, the muscle fiber density of fish in the compound herbal medicine supplement group was significantly higher than that in the CM group (P<0.05). (6) The relative expression levels of myogenic regulatory factors such as MyoD and MyoG in the muscles of largemouth bass were not significantly different among the groups (P>0.05). However, the relative expression levels of MSTN muscle growth inhibitor genes were significantly lower in the CMH6 group compared to the FM and CM groups (P<0.05). In conclusion, the study demonstrated that adding 4%—6% compound herbs to the diet improved the body and flesh colour, muscle nutrient content, and muscle texture of largemouth bass when fishmeal was replaced with Chlorella. This improvement may be attributed to the inhibition of MSTN gene expression by the compounded herbs, which promotes the growth of muscle fibers.