The purpose of this study was to develop the potential of cottonseed protein concentrate (CPC) and Clostridium autoethanogenum protein (CAP) in the diet of rainbow trout (Oncorhynchus mykiss) by evaluating the effects of substituting fishmeal with a CPC and CAP mixture on growth performance, nutrient utilization, serum biochemical indices, intestinal and hepatopancreas histology. In a basal diet containing 200 g/kg fishmeal (Con), the mixture of CPC and CAP (1:1) was used to reduce dietary fishmeal to 150, 100, 50 and 0 g/kg, to form five diets with the same crude protein and crude lipid contents (CON, FM-15, FM-10, FM-5 and FM-0). Then, the five diets were fed to rainbow trout (35.00 ± 0.05 g) for 8 weeks. The weight gain (WG) and feed conversion ratio (FCR) of the five groups were 258.72%, 258.82%, 249.90%, 242.89%, 236.57%, and 1.19, 1.20, 1.24, 1.28, 1.31, respectively. FM-5 and FM-0 groups showed significantly lower WG and higher FCR than the CON group (p < 0.05). In terms of whole-body composition, such as moisture, crude ash, and crude protein, no significant difference was observed among all the groups (p > 0.05), except that significantly higher crude lipid content was detected in the FM-0 group than in the CON group (p < 0.05). In the FM-5 and FM-0 groups, protein efficiency, protein retention, intestinal protease activity and amylase activity were significantly lower than in the CON group (p < 0.05). Compared to the CON group, the serum contents of glucose and total cholesterol in the FM-0 group as well as MDA in the FM-5 and FM-0 groups were significantly increased, and catalase, superoxide dismutase, and total antioxidant capacity were decreased (p < 0.05). In intestine and hepatopancreas histology, the intestinal villus height in the FM-5 and FM-0 groups and villus width in the FM-0 group were decreased significantly (p < 0.05), while no significant difference in hepatopancreas morphology was observed among all the groups except that some vacuolization was observed in the FM-0 group (p > 0.05). In summary, the mixture of CPC and CAP can effectively replace 100 g/kg fishmeal in a diet containing 200 g/kg fishmeal without adverse effects on the growth performance, nutrient utilization, serum biochemical, or intestinal and hepatopancreas histology of rainbow trout.

No abstract

This study investigated the effects of dietary emulsifiers and antioxidants on astaxanthin utilization and antioxidant capacity of rainbow trout. First, 50 and 100 mg kg −1 of synthetic astaxanthin (AST-50 and AST-100) were added to the control diet (Con), then 400 mg kg −1 sodium taurocholate (ST), 100 mg kg −1 tea polyphenols (TP) and 100 mg kg −1 surfactin (SUR) were added to the AST-50 diet. The six diets were fed to rainbow trout (6.69 ± 0.02) g for 6 weeks. No significant differences were found in weight gain and feed conversion ratio among all the diets (p > .05). The flesh redness (a*), yellowness (b*) and the astaxanthin content in flesh and liver were significantly increased in fish fed with ST, TP and SUR diets compared with the CON fish, but these values were lower than that in fish fed with AST-100 diet (p < .05). Diets involving TP and SUR significantly enhanced T-AOC in flesh, serum and liver, whereas T-SOD was decreased than those of AST-50 and ST diets (p < .05). In conclusion, the supplementation of tea polyphenols and surfactant in the diet effectively improved the astaxanthin deposition and antioxidant capacity of rainbow trout, and sodium taurocholate promoted the deposition of astaxanthin, rather than the antioxidant capacity.

The study investigated the effects of dietary sodium butyrate (SB) on the growth performance, nutrient utilization, intestinal histology, and microbiota of rainbow trout (Oncorhynchus mykiss). A high fishmeal diet and a low fishmeal diet were formulated to contain 200 g/kg or 100 g/kg fishmeal, respectively. Coated SB (50%) was supplemented to each of the diets at levels of 0, 1.0, and 2.0 g/kg to create 6 diets. The diets were fed to rainbow trout with initial body weight of 29.9 ± 0.2   g for 8 weeks. Compared to the high fishmeal group, the low fishmeal group showed significantly lower weight gain (WG), intestine muscle thickness, and significantly higher feed conversion ratio (FCR) and amylase activity ( P < 0.05 ). The supplementation of SB in high or low fishmeal diet did not significantly affect the WG, FCR, protein retention, and the digestibility of dry matter and crude protein ( P > 0.05 ). The supplementation of 2.0 g/kg SB in low fishmeal diet significantly increased the villus height, villus width, and muscular thickness, while the supplementation of 2.0 g/kg SB in high fishmeal diet also significantly increased the intestinal villus height ( P < 0.05 ). In intestinal microbiota, the supplementation of 2.0 g/kg SB significantly increased the abundance of Proteobacteria and Aeromonas, and decreased the abundance of Firmicutes and Mycoplasma ( P < 0.05 ), but the flora at genus and phylum level were not affected by SB supplementation in low fishmeal diet ( P > 0.05 ). In conclusion, the addition of SB in diets containing 100 or 200 g/kg fishmeal did not enhance the growth performance and nutrient utilization of rainbow trout, but improved intestinal morphology and changed intestinal microbial flora.

Dietary supplementation of functional additives is an effective strategy to improve the nutritive value of low fish meal diets for fishes. The present study is aimed at investigating the dietary effects of a multienzyme complex, an organic acid-essential oil complex and prebiotic on growth, immune function, and intestinal health of rainbow trout (Oncorhynchus mykiss). A positive control diet (PC) and a negative control diet (NC) were formulated to contain 200 g/kg and 100 g/kg of fishmeal, respectively. Seven other diets were formulated by supplementing a multienzyme complex (MC, 0.125 g/kg), organic acid-essential oil complex (OEC, 0.5 g/kg), and prebiotic (P, 2 g/kg) alone or in combination to the NC diet (MC, OEC, P, MC+OEC, MC+P, OEC+P, MC+OEC+P). All diets were formulated to be isoproteic (434.3 g/kg-439.1 g/kg) and isolipidic (119.2 g/kg-125.9 g/kg) and fed to rainbow trout of 7.66 ± 0.05   g for 56 days. The weight gain, apparent digestibility coefficient of dry matter, protein efficiency ratio, and protein retention efficiency were significantly increased, and feed conversion ratio was significantly decreased by the three additives alone or in combination ( P < 0.05 ) compared to the NC. No significant differences in growth performance and feed utilization were observed among the treatment groups. Compared to the NC group, serum alanine transaminase, aspartate transferase activities, and malondialdehyde content reduced significantly, while serum superoxide dismutase increased in all except for the MC group, and alkaline phosphatase and lysozyme activity increased in all except for the MC and MC+P groups ( P < 0.05 ). The foregut protease activity of the MC+P and OEC+P groups and the amylase activity of the OEC and MC+OEC groups were significantly higher than those of the NC group ( P < 0.05 ). The villus height of P, MC+OEC, and OEC+P groups, the villus width of MC group, and the muscle thickness of MC, MC+OEC, and MC+OEC+P groups were also significantly higher than those of the NC group ( P < 0.05 ). Compared to the PC group, the richness and diversity of intestinal microorganisms in the NC group and all the supplemented groups were significantly reduced ( P < 0.05 ), but no differences among them ( P > 0.05 ). In conclusion, the individual or combined supplementation of multienzyme complex, organic acid-essential oil complex, and prebiotic in a low fish meal diet (100 g/kg) improved the growth performance, nutrient utilization, and immune function of rainbow trout, but no synergistic effects were observed in the combination of the three supplements.