This study evaluated the effects of lipid sources on the replacement of fishmeal with Clostridium autoethanogenum protein (CAP) in the diet of Pacific white shrimp (Litopenaeus vannamei). By using CAP to replace 40% fishmeal in the basal diet (contains 25% fishmeal), four diets (PC as the control diet, LSO as the low soybean oil level, MSO as the middle soybean oil level, and HSO as the high soybean oil level) were formulated by adding different proportions of fish oil and soybean oil. Each diet was assigned to four replicates (40 shrimps per replicate, initial weight = 1.79 ± 0.02 g). A 7-day Vibrio parahaemolyticus challenge test was conducted at the end of the 50-day feeding experiment. Weight gain was significantly higher and the cumulative mortality after challenge was lower in HSO treatment. The total antioxidant capacity (T-AOC) in hepatopancreas was significantly raised with increasing dietary soybean oil based on CAP substitution. After challenge, Pen3 mRNA expression was significantly higher in hepatopancreas and NF-κB pathway-related mRNA (dorsal, relish, and IKKβ) expression was higher in the intestine in HSO treatment. The height of mucosal folds and the thickness of the muscle layer were positively correlated with the level of dietary soybean oil. Transmission electron microscopy (TEM) analysis showed that the microvilli were damaged and the endoplasmic reticulum was swollen in shrimp fed the LSO diet. Diversity of intestinal microbiota was increased in shrimp fed the LSO diet, with a significant increase in beneficial bacteria such as Halocynthiibacter and Ruegeria as well as less harmful bacteria such as Vibrio. These results suggested that the replacement of fishmeal with CAP and the high proportion of soybean oil in the diet could improve the growth performance, disease resistance, and intestinal structure of Pacific white shrimp, and high fish oil in a low-FM diet raised the percentage of beneficial bacteria in the intestine of shrimp.
This study was to evaluate the impacts of micronutrients added to low-fishmeal diet on the flesh quality and immune response of largemouth bass, Micropterus salmoides. Two diets (FM48 and FM32) were formulated with 48% and 32% fishmeal, respectively, micronutrients (Zn, Mn, Se, VB12 and niacin) were added in FM32 to formulated the LFM diet. Largemouth bass with an initial weight of 12.65 ± 0.04 g were fed with three diets for eight weeks. The results showed that the feed coefficient rate of the shrimp in LFM group was significantly lower than that of the other two groups. There were no significant differences in muscle moisture, crude protein and crude lipids content among the three groups. The activity of muscle superoxide dismutase in the LFM group and FM48 group was significantly higher than that in the FM32 group. Zn content was highest in the muscles of FM48 group, and Se was higher in the muscles of the LFM group than that in the FM48 and FM32 groups. The results of histological analysis showed that the density of muscle fibers was improved after the addition of micronutrients. RT-qPCR results suggested that the expression of ribosomal protein, mammalian target of rapamycin, and eukaryotic translation initiation factor 4E-binding protein1 in the FM48 group were significantly higher than those in the FM32 group and LFM group. The expression of myogenic differentiation 1 was significantly upregulated in the LFM group, which was significantly higher than that in the FM48 and FM32 groups. The expression of tumor necrosis factorαwas significantly upregulated in the shrimp of LFM group compared with those in other groups. These results showed that the addition of micro-nutrients in low fishmeal diet did not affect the growth of largemouth bass, while increase the contents of Mn and Se in the muscle, enhanced the antioxidant capacity, promoted the proliferation of muscle fibers of largemouth bass.
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