Beta-Agonist, Ractopamine Hydrochloride, Improves Growth, Alters Body Composition, and Suppresses Gonadal Maturation in All-Female Giant Freshwater Prawn, Macrobrachium rosenbergii

Abstract

All-female giant freshwater prawn Macrobrachium rosenbergii has a significant growth limitation due to its early sexual maturity. A 60-day trial was carried out to determine the effect of beta-agonist, ractopamine hydrochloride (RAC), on the growth performance, body composition, and gonadal maturation of all-female prawns. Prawn juveniles ( $4.39\pm 0.40$  g initial weight) were stocked at 10 prawns/m2 in 15 plastic tanks (1000 liters each) in a completely randomized design with four treatments and a control (0, 5, 10, 15, and 20 mg/kg) in triplicate. The significantly ( $p<0.05$ ) highest values of final weight, weight gain, daily weight gain, and specific growth rate (SGR) were observed in the female prawns fed with the diet containing 10 mg/kg RAC, while the lowest values were found in the control tank. Similarly, survival rate, feed conversion rate (FCR), and condition factors were observed among all treatments, which were significantly better than the control (0 mg/kg). Significantly greater yield and lower gonadosomatic index (GSI) values were obtained in prawns fed with a 10 mg/kg RAC-containing diet than in all other treatments, except for the diet containing 15 mg/kg RAC, while the lowest yield was produced by the control tank. A diet containing 10 mg/kg RAC had significantly improved the whole-body protein content in prawns, while diets containing 10 and 15 mg/kg RAC exhibited lower lipid content in prawns than in the other treatments. A significant increase in the number of Stage 1 (virgin) females (up to 54% at 10 mg/kg RAC diet) was found in all RAC treatments, while the control had a significantly higher number of females at various maturity stages, indicating that RAC administration effectively suppresses gonadal maturity. Residue analysis of whole prawn samples at the end of the trial indicated no trace of ractopamine. The quadratic regression analysis of weight gain, SGR, FCR, and yield revealed that the optimum dietary ractopamine level for all-female prawn culture should be between 10 and 15 mg/kg.