Induced ovulation of Pangasius bocourti (Sauvage, 1880) with a progressive hCG treatment

The Mekong catfish Pangasius bocourti (Pangasiidae, Siluriforme) has been widely cultured in southern Vietnam in floating cages since 1989 (15,000 tonnes annually). However, the supply of fingerlings has been dependent on catches from the wild, which has led to a reduction in the natural resources. Reproduction of P. bocourti was studied with brooders reared in earthen ponds or in floating cages on the Mekong River. Brooders did not show any sexual dimorphism but females were more developed than males in terms of body weight (+26%) and fork length (+7%), Induction of oocytes maturation and ovulation required a progressive hormonal treatment in two steps. Several daily injections of hCG at a low dose (500 IU kg(-1)) were applied first. These injections induced the development of ovarian follicles, indicated by an increase in their diameter. The second step consisted of two successive hCG injections applied at higher doses (1500 and 2500 IU kg(-1)) at an 8-10-h interval, which induced oocytes maturation, followed by ovulation at 19 3 h after the first injection. Mean ovulation and hatching rates were 66% and 55%, respectively. Ovulation was generally induced once a year for each female although a second ovulation could be obtained for some individuals in the same reproductive season. Fecundity was highly variable, from 400 to 16,700 ova kg(-1), and average fecundity in ponds was twice as high as in cages. (C) 2002 Elsevier Science B.V. All rights reserved.