Effects of new hydrogel diets on growth, digestion and apparent digestibility of nutrients of Eriocheir sinensis

While commercial diets for Chinese mitten crabs provide a diverse range of nutrients, they still have certain limitations compared to feeding with frozen trash fish (FTF), such as poor water stability. Most studies have focused on optimizing dietary formulations to address this issue, overlooking the influence of the physical properties of the diet on Eriocheir sinensis. In this study, a novel sodium alginate–based hydrogel (SAH) diet was developed to investigate the effects of its soft particle texture on the growth and digestion of E. sinensis. Growth experiment: Crabs were fed three diets with different textures—FTF, pellet diet (PED), and SAH (SA12.5 %)—over an 8-week period. The initial average weight of each group was 75.3 ± 0.75 g. No significant differences in growth performance were observed among the three diet groups. The analysis of digestive enzyme activity in the hepatopancreas showed a notable increase in trypsin activity in the SAH group compared with the FTF group, while lipase, α-amylase, and cellulase activities showed no significant differences. The examination of digestion-related gene expression in the intestine revealed notable upregulation of crtb1, il, espt, pm1, and pm2 genes in the SAH group. Additionally, gut microbiota diversity increased, whereas richness decreased in the SAH group. Apparent digestibility test: Five SAH diets with varying SA (SAH1 [SA8.33 %], SAH2 [SA9.09 %], SAH3 [SA10 %], SAH4 [SA11.01 %], and SAH5 [SA12.5 %]) were tested, with PED serving as the control (CON). The apparent digestibility of dry matter, crude protein, crude lipid, total phosphorus, and total amino acids in SAH3 and SAH5 groups was significantly higher than that in the CON. In conclusion, the SAH diet improved the digestive performance of E. sinensis without adversely affecting growth, leading to notable improvements in digestive enzyme activity and apparent digestibility.