Evaluation of spray-dried blood meal for application in commercial-like feed for juvenile swimming crab (Portunus trituberculatus)

The objective of the present study was to evaluate the effects of replacing fish meal (FM) with spray-dried blood meal (SDBM) on growth performance, antioxidant capacity, digestive enzyme activity, tissue Fe content, gene expression related to inflammation, and the TOR pathway in juvenile swimming crab (Portunus trituberculatus). Four isonitrogenous (47.0% protein) and isolipidic (9.0% lipid) diets were formulated to contain different levels of SDBM, with FM replaced by SDBM at 0, 10%, 20%, and 30%, respectively. The results showed that crabs fed diet SDBM30 exhibited the lowest survival among all treatments, and crabs fed the SDBM20 diet had the highest final weight, percent weight gain, specific growth rate and feed efficiency among all treatments. In addition, the protein content of the crab hepatopancreas decreased significantly and the lipid content increased significantly as SDBM replaced FM in the diets. Compared to other diets, crabs fed the SDBM30 diet had the lowest activities of antioxidant enzymes and the highest concentration of malondialdehyde in the hepatopancreas and hemolymph. The Fe contents in hepatopancreas and gill increased significantly, and the color of the hepatopancreas got darker as replacement of FM with SDBM increased from 0% to 30%. The expression of genes related to TOR (tor, akt, s6, and s6k1) and antioxidant (gpx) pathways in the hepatopancreas were down-regulated significantly with increased replacement of dietary FM with SDBM. In contrast, expression levels of genes related to protein translation (4ebp1, eif4e1a, eif4e2, and eif4e3) and inflammation pathways (myd88, traf6, relish, and irak4) were up-regulated significantly in crabs fed diets with SDBM supplementation. In summary, replacing FM with less than 20% of SDBM can promote the growth, but can darken the hepatopancreas, negatively affect antioxidant capacity, and induce an inflammatory response.