Effects of Replacing Fishmeal with the Mixture of Cottonseed Protein Concentrate and Clostridium autoethanogenum Protein on the Growth, Nutrient Utilization, Serum Biochemical Indices, Intestinal and Hepatopancreas Histology of Rainbow Trout ( Oncorhynchus mykiss )
Animals : an Open Access Journal from MDPI · 4 authors, 3 centres
INTERVENTIONReplacement of dietary fishmeal with a 1:1 mixture of cottonseed protein concentrate (CPC) and Clostridium autoethanogenum protein (CAP) at levels reducing fishmeal from 200 g/kg to 150, 100, 50, and 0 g/kg
COMPARISONControl diet (CON) containing 200 g/kg fishmeal with no CPC or CAP inclusion
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This study evaluated replacing fishmeal with a 1:1 mixture of cottonseed protein concentrate (CPC) and Clostridium autoethanogenum protein (CAP) in rainbow trout diets. Results showed that up to 50% of dietary fishmeal (100 g/kg out of 200 g/kg) could be replaced without negatively affecting growth, nutrient utilization, or tissue histology. Higher replacement levels (75–100%) significantly reduced growth performance, digestive enzyme activity, and antioxidant capacity while increasing serum glucose and cholesterol.
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**Background:** Rising fishmeal prices and marine resource limitations necessitate alternative protein sources in aquafeeds. Cottonseed protein concentrate (CPC) and Clostridium autoethanogenum protein (CAP) are promising substitutes due to low anti-nutrient factors and complementary amino acid profiles—CPC is rich in arginine but low in lysine and methionine, while CAP is rich in lysine and methionine but low in arginine. This study evaluated the effects of replacing fishmeal with a 1:1 CPC and CAP mixture on growth, nutrient utilization, serum biochemistry, and intestinal and hepatopancreas histology in rainbow trout (Oncorhynchus mykiss).
**Methods:** A basal diet containing 200 g/kg fishmeal (CON) was formulated. The CPC and CAP mixture (1:1) was used to progressively reduce fishmeal to 150 g/kg (FM-15), 100 g/kg (FM-10), 50 g/kg (FM-5), and 0 g/kg (FM-0), maintaining equal crude protein (430 g/kg) and crude lipid (100 g/kg) across all diets. The CPC contained 615.1 g/kg crude protein and 172.8 mg/kg free gossypol; CAP contained 842.1 g/kg crude protein. A total of 300 juvenile rainbow trout (35.00 ± 0.05 g) were randomly distributed into 15 tanks (20 fish/tank, 3 replicates/treatment) and fed for 8 weeks. Water temperature was maintained at 12–14 °C. Growth performance, whole-body composition, serum biochemical indices, intestinal digestive enzyme activity, and foregut and hepatopancreas histology were assessed.
**Key Results:** Survival was 100% across all groups. Weight gain (WG) was 258.72% (CON), 258.82% (FM-15), 249.90% (FM-10), 242.89% (FM-5), and 236.57% (FM-0). Feed conversion ratio (FCR) was 1.19, 1.20, 1.24, 1.28, and 1.31, respectively. FM-5 and FM-0 groups showed significantly lower WG and higher FCR than CON (p < 0.05). No significant differences in whole-body moisture, crude ash, or crude protein were observed among groups (p > 0.05), but crude lipid was significantly higher in FM-0 (71.1 g/kg) than CON (64.9 g/kg) (p < 0.05). Intestinal protease activity decreased progressively: 16.10 (CON), 14.26 (FM-15), 10.32 (FM-10), 8.16 (FM-5), and 5.12 U/mg prot (FM-0), with FM-10, FM-5, and FM-0 significantly lower than CON (p < 0.05). Amylase activity was significantly lower in FM-5 (0.44) and FM-0 (0.34) vs. CON (0.70) (p < 0.05). Protein efficiency ratio (PER) and protein retention (PR) were significantly lower in FM-5 and FM-0 vs. CON (p < 0.05). Serum glucose (GLU) was significantly elevated in FM-0 (5.47 mmol/L) vs. CON (4.67 mmol/L) (p < 0.05). Total cholesterol (TCHO) was significantly higher in FM-0 (8.32 mmol/L) vs. CON (7.11 mmol/L) (p < 0.05). Malondialdehyde (MDA) was significantly increased in FM-5 (16.45 nmol/mL) and FM-0 (16.29 nmol/mL) vs. CON (14.03 nmol/mL) (p < 0.05). Superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) were significantly lower in FM-5 and FM-0 vs. CON (p < 0.05). Intestinal villus height was significantly reduced in FM-5 (670.4 μm) and FM-0 (603.1 μm) vs. CON (734.9 μm) (p < 0.05). Villus width was significantly reduced only in FM-0 (127.6 μm vs. 161.9 μm in CON) (p < 0.05). Muscle thickness was significantly lower in FM-5 (120.0 μm) and FM-0 (119.4 μm) vs. CON (140.6 μm) (p < 0.05). Hepatopancreas morphology showed vacuolation and lipid droplets in FM-0 but no abnormalities in other groups.
**Clinical Implications:** The 1:1 mixture of CPC and CAP can effectively replace up to 100 g/kg fishmeal (50% replacement) in a diet containing 200 g/kg fishmeal without adverse effects on growth, nutrient utilization, serum biochemistry, or intestinal and hepatopancreas histology in rainbow trout. Higher replacement levels (75–100%) significantly impair growth, reduce digestive enzyme activity and antioxidant capacity, and increase lipid deposition and serum stress markers. The complementary amino acid profiles of CPC and CAP likely contribute to the successful partial replacement. These findings support the use of combined alternative proteins to develop low-fishmeal diets for sustainable rainbow trout aquaculture.
Replacement of dietary fishmeal with a 1:1 mixture of cottonseed protein concentrate (CPC) and Clostridium autoethanogenum protein (CAP) at levels reducing fishmeal from 200 g/kg to 150, 100, 50, and 0 g/kg