Comparison effect of Rhodobacter sphaeroides protein replace fishmeal on growth performance, intestinal morphology, hepatic antioxidant capacity and immune gene expression of Litopenaeus vannamei under low salt stress

The present study was conducted to evaluate the effect of replacing fishmeal (FM) with Rhodobacter sphaeroides protein on growth performance, intestinal morphology and antioxidant capability of Pacific white shrimp (Litopenaeus vannamei) in an eight-week feeding experiment. FM protein of a FM-based control diet (FM20) was replaced with 0 (FM20), 4 (FM16), 8 (FM12), 12 (FM8), 16 (FM4), and 20% (FM0) by Rhodobacter sphaeroides protein to formulate six experimental diets. Compared with control group, the shrimp fed 4% (FM16) and 8% (FM12) Rhodobacter sphaeroides protein gained higher survival rate and specific growth rate (SGR). There were no significant differences in MDA content of hepatopancreases and crude protein in whole body, while crude lipid was increased significantly in shrimp fed with Rhodobacter sphaeroides protein. In addition, there was no negative impact on the intestinal morphology of shrimp by FM replacement with Rhodobacter sphaeroides protein. The challenge test with low salt stress showed that the survival rate of shrimp fed with Rhodobacter sphaeroides protein were not significantly different from that of shrimp fed with whole fishmeal. Furthermore, higher T-AOC and GSH-PX activities of hepatopancreases of shrimp were observed in Rhodobacter sphaeroides protein after low salt stress. Moreover, compared with the control group, substitution of Rhodobacter sphaeroides significantly improved the resistance of L. vannamei against the stress of acute low salinity, as indicated by higher expression levels of SOD, Relish and HSP70 and lower expression levels of Caspase-3. Our findings suggested that Rhodobacter sphaeroides protein, has improved growth performance and maintained the intestinal tract healthy, and enhanced antioxidant competence and immunity of L. vannamei and could serve as novel FM replacement in shrimp feed that helps shrimp to overcome low salt challenge.