The resistance to physical stresses by Penaeus monodon juveniles fed diets supplemented with astaxanthin

This study was aimed to determine if the increase of body astaxanthin content through dietary supplementation in tiger prawn Penaeus monodon juvenile could enhance its antioxidant defense capability and resistance to thermal and osmotic stress. Hemolymph total antioxidant status (TAS) and superoxide dismutase (SOD) were chosen as indices of shrimp antioxidant capacity. Resistance to thermal and osmotic stress was expressed as shrimp recovery, and hemolymph aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Tiger prawn 5-day postlarvae were fed diets supplemented with 0 or 80 mg astaxanthin/kg diet for 8 weeks so that the resulting juveniles contained two levels of astaxanthin. Subsequently, shrimp were subjected to a rapid change in water temperature (27 to 5 degrees C) and/or salinity (32 per thousand to 0 per thousand) for 5 min. The treated shrimp contained markedly higher body astaxanthin than the control shrimp. Significantly higher average recovery in treated shrimp (56%) than control shrimp (48%) suggested that astaxanthin supplement had improved the resistance against thermal and osmotic stress. Thermal stress had a more profound effect than osmotic stress on the recovery of shrimp, as indicated by the difference in recovery, 73% versus 24%. TAS was improved and SOD was reduced by the presence of dietary astaxanthin. The enhancement of antioxidation capacity by dietary astaxanthin and consequently, the improvement of recovery against thermal and osmotic stress have demonstrated that astaxanthin is a 'semi-essential' nutrient for tiger prawn. The presence of astaxanthin can become critical when the animal is under physiological stress caused by abiotic changes. However, complicated interactions were observed among thermal and osmotic stresses and improvement of resistance conferred by dietary astaxanthin. Shrimp hepatopancreatic function may have been improved by dietary astaxanthin since hemolymph AST of the control shrimp was significantly higher than that of the treated shrimp. However, hemolymph AST and ALT content of shrimp did not reflect improvement in health following thermal and osmotic stresses, respectively.