The effects of eyestalk ablation on the reproductive and immune function of female Macrobrachium americanum

Eyestalk ablation is the most common procedure used to induce crustacean reproduction in commercial hatcheries. However, other physiological and metabolic processes are affected by the removal of the X-organ sinus gland complex located in the eyestalk. In this study, the effect of unilateral eyestalk ablation on the concentration of several hemolymph metabolites, reproduction and immune function in female Macrobrachium americanum was investigated. Molting cycle time was not significantly (P=0.17) shortened in eyestalk-ablated females. However, an increased number of molts was observed in the eyestalk-ablated group because survival was significantly higher due to increased passivity and lowered aggression. As M. americanum has closed thelyca, reproduction was not accelerated after eyestalk ablation compared to control prawns. Food intake (P=0.007) and oxygen consumption (P=0.047) were both higher in eyestalk-ablated females. Concentrations of protein and glucose in hemolymph were not affected (P=0.54 and P=0.19, respectively), indicating that the demand for these metabolites was met. Glucose was metabolized by aerobic metabolism as shown by the lower lactate concentration (P=0.02) and higher respiration rate after ablation. Protein was metabolized for growth as revealed by the 100% higher growth rate in eyestalk-ablated females (P=0.017). Triglycerides were more highly concentrated (P=0.02) in eyestalk-ablated females. This difference was most likely due to being transported from the digestive gland to the gonad.By analyzing the immune system it was observed that only the total hemocyte count was higher (P=0.002) in eyestalk-ablated females. The protein content in hemocytes, the prophenol oxidase system and the coagulation time were not affected. In conclusion, the eyestalk ablation procedure did not cause female M. americanum to have more reproductive events over time. Despite this failure to accelerate reproduction, eyestalk ablation reduced aggression, and thus increased survival, and promoted superior growth. This result suggests that eyestalk ablation is promising for the cultivation of M. americanum.