Effects of Foods on Maturity and Spawning Induction Methods on Ovulation of Rice Field Eel Monopterus albus (Zuiew, 1793) in Thua Thien Hue Province, Vietnam

Adult rice field eels with 125.52 ± 27.99 g body weight corresponding to 44.79 ± 5.93 cm in length were maturity cultured in a 5 m cement tank without mud for three months with density 30 eels/m. Eel broodstocks were fed with three types of food including: sea fish (T1), commercial pellet food (T2) and mixed food—50% sea fish and 50% commercial pellet food (T3). Result showed that the maximum gonadosomatic index (GSI) of female eels fed by sea fish (2.89% ± 0.67%) was higher than both commercial pellet food (1.62% ± 0.62%) and mixed food (2.03% ± 0.82%) (P < 0.05), while, GSI of male eels was 1.27% ± 0.31%, 0.68% ± 0.23% and 1.14% ± 0.41% (P > 0.05). Maturity rate of female fed by sea fish (88.91% ± 9.64%) was higher than commercial pellet food (61.12% ± 9.64%) (P < 0.05). The maturity rate of male eels was rather low and there was not significantly different among treatments (P > 0.05). Then. the eels were induced for spawning with two kinds of hormones, including T1: human chorionic ganadotropin (HCG) at 1,500 IU/kg, T2: luteinzing hormone-releasing hormone (LHRH-a) at 150 μg/kg and domperidon 10 mg/kg, and T3: control without hormone. The results of spawning induction methods showed that the reproduction rate of female eels induced by LHRH-a and HCG hormones were higher than that by natural reproduction method (P < 0.05). Others, the survival rate of fry eels after 5 d using natural reproduction method (92.65% ± 2.54%) was higher than both using LHRH-a (67.77% ± 1.91%) and HCG (68.65% ± 1.23%) hormones (P < 0.05). The average diameter of eggs was 3.40-3.41 mm and the length of newly hatched eels was 1.72 ± 0.19 cm.