High protein diet alleviates the high pH stress in Chinese mitten crab Eriocheir sinensis

This study evaluates whether a higher level of dietary protein could alleviate pH stress in Chinese mitten crab. Three diets with protein levels at 30%, 35% and 40% were used to feed crab for 8 weeks to determine the differential effect of dietary protein on growth, antioxidant capacity, inflammatory response and apoptotic factors at normal pH (7.8) and high pH (9.5) values. The pH elevation depressed growth performance in terms of weight gain (WG), specific growth rate (SGR) and feed conversion rate (FCR), but this effect significantly depended on the level of dietary protein. The higher level of protein significantly improved WG, SGR and FCR at high pH. Besides, high pH weakened the antioxidant capacity of crab fed the 30% protein diet by decreasing glutathione (GSH) in the hepatopancreas, and resulting significantly higher malondialdehyde crab fed 30% protein than those fed other two protein levels. The dependent effect of dietary protein and pH was also found in antioxidant capacity. The higher protein diet increased GSH, superoxide dismutase and glutathione S-transferase in the hepatopancreas at high pH. In addition, high pH triggered pro-inflammatory and pro-apoptotic factors in the 30% protein group by upregulating the pro-apoptotic and pro-inflammatory genes including lipopolysaccharide-induced TNF-alpha factor, p38 mitogen-activated protein kinase, a disintegrin and metalloproteinase domain-containing protein 17, Bcl-2-associated X and Cysteine-aspartic acid protease 3. The higher protein diets downregulated pro-apoptotic and pro-inflammatory genes at high pH. In conclusion, the high pH caused a marked growth retardation and poor feed efficiency, triggered oxidative stress and pro-inflammatory and increased pro-apoptotic factors in crab fed the low protein diet. Higher protein diets alleviated the negative effect of pH in the Chinese mitten crab. This study suggests that a higher protein diet can counteract the negative effect of high pH in Chinese mitten crab farming.