African Journal of Aquatic Science 2010, 35(1): 81–85 Printed in South Africa — All rights reserved Copyright © NISC (Pty) Ltd AFRICAN JOURNAL OF AQUATIC SCIENCE ISSN 1608–5914 EISSN 1727–9364 doi: 10.2989/16085914.2010.466586 African Journal of Aquatic Science is co-published by NISC (Pty) Ltd and Taylor & Francis Reproductive strategy of Labeo senegalensis Valenciennes 1842 (Teleostei: Cyprinidae) in the Ouémé basin, Benin E Montchowui 1 , P Lalèyè 2 *, P Poncin 3 and J-C Philippart 3 1 Behavioural Biology Unit and Laboratory of Fish Demography and Hydroecology, University of Liège, 22 quai Van Beneden, 4020 Liège, Belgium; current address: Laboratory of Hydrobiology and Aquaculture, University of Abomey-Calavi, 01BP526 Cotonou, Benin 2 Laboratory of Hydrobiology and Aquaculture, University of Abomey-Calavi, 01BP526 Cotonou, Benin 3 Behavioural Biology Unit and Laboratory of Fish Demography and Hydroecology, University of Liège, 22 quai Van Beneden, 4020 Liège, Belgium * Corresponding author, e-mail: philippe.laleye@fsa.uac.bj Received 9 June 2009, accepted 11 August 2009 Aspects of the reproductive biology and population structure of Labeo senegalensis were investigated in the Ouémé River between April 2005 and March 2006. Reproductive strategy was investigated using gonadosomatic index, ovarian structure and fecundity. Average size-at-first-maturity (L 50 ) was estimated at 29 cm TL for females and 25.7 cm TL for males. The average sex ratio (1:0.96) was not significantly different from unity. Oocyte diameter frequency distribution suggests synchronous development with a single total spawning. Absolute fecundity ranged between 12 948 and 74 832 eggs. Labeo senegalensis is a highly fecund fish that presents a seasonal cycle of reproduction from May to October during the rainy season. Keywords: fecundity, population structure, reproduction, sex ratio Introduction Fish species of the genus Labeo Cuvier 1817 are widely distributed throughout Africa and consist of at least 80 species comprising 16.4% of the African cyprinid ichthyo- fauna (Reid 1985). Most Labeo species are commercially important throughout the African continent, and contribute significantly to various fisheries (Weyl and Booth 1999, Delaney et al. 2007). Labeo senegalensis Valenciennes 1842 is widely distrib- uted throughout West Africa (Lévêque 2003). It attains a length of 65.0 cm TL, a maximum weight of just under 4 kg and a maximum age of six years (Lévêque and Daget 1984). Labeo senegalensis, locally called ‘Gbogbé’, is the larger of the two Labeo species present in the Ouémé River (Lalèyè et al. 2004) and is an important species in catches, as well being as a popular food fish. Therefore, it currently experi- ences a high fishing pressure (Montchowui et al. 2008). Despite its commercial importance and possible use as an aquaculture species in the tropics (Omoreigie 2001), only very limited and disparate information exists on its reproductive biology. With the increase of fishing activities in the Ouémé River in Benin, L. senegalensis is in danger of being overex- ploited. Management plans are necessary for its rational exploi- tation. This study was initiated in order to provide information on some aspects of its reproductive biology, such as spawning period, size-at-first-maturity, fecundity and sex ratio, which can be used in order to manage the fishery properly. Materials and methods Study site The Ouémé (Figure 1) is the largest river basin in Benin, with a 50 000 km 2 catchment area over 510 km in length from the Tanéka mountains in the north of the country to the eastern side of Lake Nokoué (Colombani et al. 1972). Peak discharge occurs in August and September. The river has an average slope of 0.9 m km −1 , except along the upstream area of the basin where it descends at 20 m km −1 . Due to its geographic location this river is influenced by two distinct climates. In the north the climate is character- ised by a tropical trend of alternate dry and rainy seasons with wide-ranging temperatures (10–40 °C). From November to March, rains may be scarce or turbulent. Furthermore, the ‘Harmattan’ wind, which blows from November to April, accentuates the thermal and hygrometric amplitudes. The rainy season extends from May to September. The southern part of the basin is influenced by a subequatorial climate with two rainy and two dry seasons. The long rainy season runs from April to July with the highest rainfall in June. The short rainy season starts in September. Temperatures range from 18 °C to 35 °C. Fish sampling took place at four stations (Figure 1). Station 1, on the Ouémé River at Bétérou (09°11′ N, 02°16′ E), was along a rocky zone with swift currents. Station 2, at Atchakpa (08°04′ N, 02°22′ E) on the Ouémé River, was characterised by a rocky zone. Station 3, at