Induced ovulation of Pangasius bocourti (Sauvage, 1880) with a progressive hCG treatment Philippe Cacot a, * , Marc Legendre b , Tran Quoc Dan c , Le Thanh Tung d , Pham Than Liem d , Catherine Mariojouls e , Jerome Lazard a a CIRAD (Centre de Coope ´ration Internationale en Recherche Agronomique pour le De ´veloppement), TA 30/01, Avenue Agropolis, 34398 Montpellier Cedex 5, France b IRD (ex ORSTOM) (Institut de Recherches pour le De ´veloppement), Instalasi Penelitian Perikanan Air Tawar, Jl. Ragunan-Pasar Minggu, P.O. Box 7220/jkspm, 12540 Jakarta, Indonesia c AGIFISH Co. (Angiang Fishery Company), La Thanh Than street, Chaudoc City, Angiang Province, Viet Nam d Institute of Aquaculture and Fishery Sciences, Cantho University, Cantho City, Haugiang Province, Viet Nam e De ´partement des Sciences Animales, Institut National Agronomique Paris-Grignon, 16, rue Claude Bernard, 75231 Paris Cedex 5, France Received 19 August 1999; received in revised form 18 January 2002; accepted 21 January 2002 Abstract 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 À 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 À 1 ) at an 8 – 10-h interval, which induced oocytes maturation, followed by ovulation at 19 F 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 0044-8486/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0044-8486(02)00033-9 * Corresponding author. Tel.: +33-4-67-04-63-00; fax: +33-4-67-63-57-95. E-mail address: philippe.cacot@cirad.fr (P. Cacot). www.elsevier.com/locate/aqua-online Aquaculture 213 (2002) 199 – 206