| Terrestrial animal protein sources contain less antinutritional factors, high protein content, and functional factors which are beneficial to fish health. Among them, poultry by-product meal (containing 65 %~73 % protein, rich in vitamin) and porcine meat meal (containing 45 %~60 % protein and high contents of proline and glycine) are the most widely used in aquatic compound feeds, and are important fish meal replacement sources. As a carnivorous fish species, largemouth bass is highly dependent on dietary fish meal, and the level of fish meal added in its commercial feeds is up to 50%. However, the rising price of fish meal increases the farming cost of largemouth bass. Therefore, it is urgent to find a suitable alternative protein source to reduce the amount of dietary fish meal and reduce the feed cost. In this consideration, 7 compound feeds (D1-D7) were prepared in this study. The added percentages of fish meal/poultry by-product meal/porcine meat meal are: 45.0 /22.6 /0, 37.1 /22.6 /8.0, 28.8 /22.6 /16.0, 45.0 /14.5 /8.0, 45.0 /5.3 /16.0, 41.6 /18.0 /8.0, 37.0 /13.8 /16.0. Juvenile largemouth bass (initial body weight ~55 g) were fed the above diets for 60 days with five replicates in each group. The effects of animal protein source combination on the growth performance, tissue biochemical indices, muscle texture characteristics, liver protein metabolism and intestinal inflammatory factors related gene expression were evaluated. The water temperature during feeding trial was 27.4℃-32.3 ℃, and the ammonia nitrogen was 0.1-0.2mg/L. After the feeding experiment, three fish were randomly selected from each cage to collect serum, liver, intestinal tract, muscle and other samples, which were then stored at -80℃. In addition, three fish were randomly selected for each cage to determine the morphological indices of fish body. At the same time, two fish were selected from each cage for the determination of muscle texture characteristics and the whole fish proximate composition. Physiological and biochemical indices of serum and liver tissues (albumin (ALB), urea nitrogen (BUN), total amino acid (T-AA), alanine aminotransferase (ALT), aspartate aminotransferase (AST), total protein (TP), blood ammonia (SA)) was determined by the commercial kits, and the texture characteristics of muscle were determined by the texture analyzer. The moisture, crude fat, crude protein and ash contents of whole fish and muscle were determined by atmospheric drying, Soxhlet extraction, Kjeldahl nitrogen determination and Muffle furnace incineration, respectively. Real-time quantitative PCR (qPCR) were used to determine the expression levels of genes related to liver protein metabolism and intestinal inflammatory response. All test data were expressed as mean ± standard error, and multiple comparisons were made by Tukey test, with P < 0.05 indicating the significant difference. The results showed that: compared with other groups, the final body weight, weight gain rate and specific growth rate of fish in the D3 group were significantly higher, and the feed conversion ratio was significantly lower (P < 0.05). There were no significant differences in condition factor, hepatosomatic index, viscerosomatic index and survival rate among all groups (P > 0.05). The whole body crude protein content in the D3 group was significantly higher than that in the D1 group, and the crude lipid level in the D3 group was significantly lower than that in the D6 group (P < 0.05). In terms of tissue physiological and biochemical indices, there were no significant differences in the activities of BUN and ALT in serum, SA content and ALT activity in liver among all groups (P > 0.05). The serum T-AA content of fish in the D3 group was significantly higher than that in the D1 and D4 groups (P < 0.05), but the AST activity in the D3 group was significantly lower than that in the D5 group (P < 0.05). The liver TP content in the D3 group was significantly higher than that in the D7 group (P < 0.05). There were no significant differences in serum TP content and liver ALT in the D3 group compared with other groups (P > 0.05). In terms of muscle quality, the muscle hardness, adhesion and mastication in the D3 group was significantly lower than those in the D4 and D6 groups, respectively (P < 0.05). There were no significant differences in the muscle adhesiveness, elasticity, cohesiveness, moisture, crude protein content, crude lipid content and ash content among all groups (P > 0.05). In addition, the mRNA expression levels of intestinal il-10 and liver tor, s6k1, akt and pi3k in the D3 group were up-regulated, which were significantly higher than those in the D7 group (P < 0.05). The mRNA expression levels of il-1β and il-6 in intestine and 4ebp-1 in liver of the D3 group were and significantly lower than those in the D1 group (P < 0.05). These results indicate that combined use of 28.8% fish meal, 16.0% porcine meat meal and 22.6% poultry by-product meal have the best growth promotion effect on M. salmoides, and is able to improve the liver protein synthesis and maintain the intestinal health. The results of this study provided technical support for reducing the dependence of largemouth bass compound feed on fish meal. |
