Supplementation of dietary astaxanthin alleviated oxidative damage induced by chronic high pH stress, and enhanced carapace astaxanthin concentration of Chinese mitten crab Eriocheir sinensis

Abstract

The Chinese mitten crab Eriocheir sinensis is subjected to high pH stress and a shortage of astaxanthin (AX) via the natural food chain when individuals are reared in ponds. The aim of this study was to investigate the response of Chinese mitten crab to chronic high pH stress, focusing on the antioxidant capacity and oxidative damage response of the crab; the potential improvement in color due to AX supplementation in the diet was also explored. Twelve tanks (400L) were used to store 30 crabs (56.5±2.3g) each. The pH of the water in 6 of the tanks was modulated to 9.5–10.0 (high pH), and another 6 tanks had a pH range of 7.5–8.1 (normal pH). Diets with or without 68mg/kg of astaxanthin were fed to crabs, with 3 tanks for each diet at each pH level. After 4weeks, reactive oxygen species (ROS) produced in hemolymph cells, activity of total superoxide dismutase (T-SOD), total antioxidant capacity (T-AOC), activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the serum, apoptotic ratio of hemolymph cells, hepatopancreas histology, hepatosomatic indices (HSI) and carapace AX concentration were analyzed. The results showed that when crabs were fed a diet without AX, high pH stress induced an increase (P<0.05) in ROS production, the apoptotic ratio of hemolymph cells, and the activity of ALT and AST as well as a decrease (P<0.05) in the activity of serum SOD, T-AOC values, and HSI values. High pH stress also led to damage of the tissue structure of the hepatopancreas. When AX was supplied, the symptoms induced by high pH stress were generally improved. Supplementation of AX enhanced the AX concentration in the carapace regardless of whether the crab was reared in water with a normal or high pH. However, a significant difference (P<0.05) was only detected in carapace AX concentration when the pH was normal. These results indicated that chronic high pH stress caused oxidative damage in Chinese mitten crab, and supplementation of AX in the diet not only alleviated oxidative damage but also improved crab body color.