Evaluation of ratios of fish-to-soybean oils on growth, lipid and cholesterol metabolism and muscle metabolites of Pacific white shrimp (Litopenaeus vannamei) fed low fishmeal diets containing Clostridium autoethanogenum protein

Abstract

The present study aims to investigate the effects of ratios of fish-to-soybean oils in a low fishmeal diet containing Clostridium autoethanogenum protein (CAP) on the growth and metabolism of Litopenaeus vannamei. Four diet groups were designed and the basal diet (FM, 44% crude protein, 8.66% crude lipid, fish-to-soybean oil: 1.5:2.5) contained 25% fishmeal. After 40% of fishmeal protein was replaced by CAP, three different fish-to-soybean oil ratios (4:1, 1:1, and 1:4) were set to formulate three experimental diets, and referred as HF (high fish oil), MF (medium fish oil), and LF (low fish oil), respectively. Shrimp were distributed to four groups of three replicates, each with 40 shrimp in a 300-L tank and they were fed four times daily for 7 weeks before sampling. Results showed that the growth performance of shrimp fed the MF diet was significantly lower than those fed the FM diet, while the shrimp fed the LF diet showed better growth than the HF group. The reduction of the crude lipid content of the whole body, hemolymph total cholesterol (T-CHO), and low-density lipoprotein cholesterol (LDL-C) contents indicated an alteration in the lipid and cholesterol metabolism of shrimp. Compared to the FM group, the mRNA levels of fas in shrimp fed the HF diet were significantly downregulated, while the mRNA levels of delta-24-sr in the HF group were significantly upregulated. In addition, the mRNA levels of hmgcr and scp in shrimp fed the LF diet significantly upregulated compared to the FM group. Metabolomic results showed that multiple metabolic pathways were affected by diet factors, including several amino acid metabolisms, purine metabolism, energy metabolism, and glycerophospholipid metabolism. In conclusion, the reduction of the ratios of fish-to-soybean oils in the low fishmeal diet containing CAP can not only reduce the usage of fish oil and the cost of feed but also maintain the growth performance of shrimp.