Philippe Laleye

Spatial and seasonal distribution of the ichthyofauna of Lake Nokoué, Bénin, west Africa

The fish biodiversity of Lake Nokoué, a lagoon in Bénin, was monitored for one year from August 2000 to July 2001 by means of samples from the artisanal fishery collected once a month at three stations. A total of 5 933 fish weighing 95 322g (mean individual weight 16.0g) belonging to 51 species, 47 genera and 34 families were sampled. An abundance of juveniles was observed, confirming the importance of the lake as nursery grounds, rich in exploitable habitats like other tropical estuaries and lagoons. The fish fauna comprised three main components: i) an estuarine component (strict, freshwater and marine origins) which is the basis of the lagoon fauna community and which is stable in space and time; ii) a marine component containing fishes which appeared in the lagoon during the dry season where the salinity remains high (>20‰) and iii) a freshwater component with fishes coming into the lagoon from the river during the flood period. The magnitude of the spatial and seasonal fluctuations of the last two components varies depending on the area: marine (Zogbo), freshwater (Vêki) or intermediate (Ganvié). The global species richness and the relative abundances of fish vary between stations and from month to month. November, with 20 species on average, and January, with 6 species on average, are significantly different as regards species richness.

Reproductive strategy of Labeo senegalensis Valenciennes 1842 (Teleostei: Cyprinidae) in the Ouémé basin, Benin

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 senegalensisis a highly fecund fish that presents a seasonal cycle of reproduction from May to October during the rainy season.

Population structure and reproductive biology of Schilbe intermedius (Teleostei: Schilbeidae) in the Pendjari River, Benin

This study, the first on fish reproduction in the Pendjari River, investigated aspects of the reproductive biology of Schilbe intermedius. A total of 429 females and 239 males were collected from March 2007 to February 2008. Females were larger than males and the sex ratio was 1:1.8 in favour of females. Size at first maturity was estimated to be 14.9 cm and 16.1 cm for males and females, respectively. Absolute fecundity ranged from 1 006 to 83 980 (22 421 ± 16 083) oocytes, and mean relative fecundity was 201 ± 162 oocytes g−1 of total body mass. Frequency distributions of oocyte diameter suggested synchronous development, with total spawning. Spawning lasted from June to November, coinciding with peaks in rainfall and flooding. Larger females began spawning about two months before smaller ones.

The role of macroinvertebrates in the diets of the dominant fish species in Lake Nokoué, Benin

Between 2003 and 2006 the diets of 22 fish species, comprising approximately 90% of the Lake Nokoué fish biomass, were analysed. Macroinvertebrates dominated the diet of ten species, fishes were the preferential prey of six fish species, and detritus and phytoplankton dominated the diets of six others. Attempts were made to calculate the consumption by fish of the main zoobenthic invertebrate groups, and this was estimated at 344 g m2 y-1. Insects constituted only 10% of the invertebrates consumed, mainly by Chrysichthys nigrodigitatus. One third of the macroinvertebrates consumed by fish comprised annelids, 20% were small crustaceans and 40% comprised shrimps, molluscs and crabs. These results are compared with published information on benthic invertebrate production within the lake, and show that some groups of macroinvertebrates are not consumed in proportion to their biomass and productivity.

Designation of a neotype for Synodontis schall (Bloch and Schneider, 1801) and description of two new species of Synodontis (Siluriformes: Mochokidae)

A morphometric study of 105 specimens of Synodontis schall, including most type specimens of all nominal species considered junior synonyms of S. schall has been undertaken. Two new species S. ouemeensis and S. kogonensis are described from the Ogun (Nigeria), Oueme (Benin) and Mono (Togo) basins, and the Kogon and Fatala (Guinea) basins, respectively. A neotype is designated for S. schall. The two new species differ from S. schall mainly by the width of the premaxillary toothplate (12.9–24.3% HL for S. schall vs. 21.6–32.7% HL), and can be distinguished one from the other by differences in orbit diameter (20.5–26.8% HL for S. ouemeensis vs. 19.4–21.0% HL for S. kogonensis) and prepectoral length (23.4–28.2% SL for S. ouemeensis vs. 21.6–23.3% SL for S. kogonensis).

Artisanal gill-net fishery catches of the catfish, Schilbe intermedius (Teleostei: Schilbeidae), in two tributaries of the Ouémé River, Bénin, West Africa

Artisanal fishery gill-net catches of the catfish Schilbe intermedius were studied in the Okpara and Zou tributaries of the Ouémé River, Benin in 1999 and 2000. The largest fish caught at the Toué and Kpassa stations measured 26.2cm and 24.5cm (TL) respectively. The success of artisanal fishing for schilbeids varied during the day, with the highest fish catches being recorded at approximately 22h00 and at 07h00 and the lowest between 13h15 and 16h15. The monthly production at Kpassa varied between 9.0g and 900.0g (average 206.3g) and between 3.3g and 17 320g (average 2 603.4g) at Toué. The monthly production fluctuated considerably. At the two stations, fewer fish were caught each month in the second year than in the same months in the first year. Nets of between 10 and 15mm stretch mesh were the most efficient. Above 15mm, gill-net fishing became less effective. Large fish were often taken with gill-nets of 20–30mm stretch mesh. Beyond these mesh sizes, the gill-net yield and catch decreased.

Production Cost of Heterobranchus longifilis (Valenciennes, 1840) Fingerlings in the Ponds Fertilized with Poultry Droppings

This study aims to evaluate the production cost of Heterobranchus longifilis larvae reared in fertilized fish ponds. Experiment was carried out in two fish ponds. Each fish pond was filled with 200 liters of water and fertilized with dry poultry droppings (dose: 0.6 g.L) and zooplankton was inoculated with 83±13 individuals/L. Six days after inoculation of zooplankton, larvae of H. longifilis of 2 days after post-hatching were directly introduced into ponds with 300 individuals/m. These larvae used exclusively zooplankton during the first 7 days. From the 8th day, larvae were fed with Coppens feed until 30 days. At the end, the survival rates were ranged between 58.33% and 56.67%. Final mean weights were brought up to all the ponds and were not significantly different (p > 0.05). The production costs ranged between 2.55 FCFA and 2.60 FCFA per fingerling with ratio production cost/weight gain around 0.80 FCFA/g in each pond. Then, this production system of fingerlings in fertilized ponds is very efficient and could be popularized in the rural fish farms.

Reproductive traits of the freshwater oyster Etheria elliptica (Bivalvia: Etheriidae) in the Pendjari River, Benin: implications for conservation

The African freshwater oyster Etheria elliptica, which is of great economic importance throughout the continent, is facing overharvesting in many fisheries in West Africa. Its reproductive traits (sex ratio, size at sexual maturity, oocyte diameter and fecundity) were studied at four stations located along the Pendjari River, northern Benin, in April 2013. Histological techniques were implemented to identify sex and gonad development stages. Oocyte sizes were measured based on the histological images and mean oocyte diameter was 38 µm. Fecundity, estimated by counting the developing eggs, averaged 106 724 eggs and increased significantly with shell size. The average sex ratio was approximately 1:1. Hermaphrodites were rare. Males reached sexual maturity at 57.6 mm dorsoventral height, earlier than females at 64.7 mm. The majority of the oyster specimens were in ripe-spawning stages, indicating that reproductive activities partly took place towards the end of the dry season. Both mature and immature individuals were subjected to harvesting at all the investigated fishing sites. The mean size of exploited oysters was 60.6 mm, lower than the size of females at maturity. Management strategies must enforce the minimum size of 65 mm required for harvesting, particularly in open access sites where juveniles are mostly harvested.

Spatialisation des paramètres physico-chimiques dans les pêcheries de la Basse Vallée de l’Ouémé (sud-Bénin).

Objectif : La Basse Vallee de l’Oueme est situee au Sud Est du Benin. Elle comporte de vastes plaines d’inondation dont les caracteristiques ecologiques favorisent une importante colonisation par les poissons. L’objectif de cette etude est de contribuer a une meilleure connaissance de la repartition spatiale des parametres physico-chimiques dans ses differentes pecheries Methodologie et resultats : Les donnees relatives aux caracteristiques physico-chimiques ont ete collectees mensuellement de mai 2014 a avril 2015 dans 16 pecheries integrees a la basse vallee de l’Oueme. Ces principaux parametres tels que la Conductivite (>S/cm), l’oxygene dissous (mg/l), le pH, la temperature (°C), le taux de saturation (%) et le TDS (Taux des Solides Dissouts) en mg/l ont ete mesures par divers appareils appropries. La methode de Krigeage ordinaire est appliquee pour estimer les valeurs des observations a des points inconnus. La modelisation des variogrammes pour les 16 stations donne trois types de modele : Un modele spherique avec effet de pepite de 0,0006 et un palier de 0.009 pour la conductivite. Un modele lineaire pour la temperature et le pH avec effet de pepite. Et des modeles periodiques avec une composante en cosinus pour le TDS, la conductivite et l’oxygene dissous. Ces modeles confirment la grande variabilite spatiale et temporelle des parametres physico-chimiques suivant le regime hydrologique de la Basse Vallee de l’Oueme. Certaines variations sont proches des seuils de tolerance admis pour la survie de la plupart des especes de poissons d’eau douce. Conclusion et application : Les principaux resultats montrent que les differentes concentrations obtenues sont tres proches des seuils de tolerance physico-chimiques de certaines especes de poissons vivant dans le milieu. Cependant, ces resultats renseignent quelque peu sur les menaces potentielles pour la survie des especes aquatiques dans ce milieu. Cette etude vise a contribuer a la prise de decision au profit de l’amenagement de la Basse Vallee de l’Oueme. Mots-cles : spatialisation- parametres physico-chimiques Basse Vallee de l’Oueme, Kregeage.

Co-culture Clarias gariepinus-Oreochromis niloticus : quels avantages pour l’amélioration des performances zootechniques et économiques des poissons élevés dans les « whedos » du delta de l’Ouémé au Bénin ?

L’alimentation des poissons est la contrainte majeure pour l’emergence de la pisciculture tropicale. Dans le but d’evaluer l’effet de la co-culture Clarias gariepinus - Oreochromis niloticus sur la croissance de ces deux especes elevees dans les whedos, une experience a ete conduite durant 56 jours dans le village Aize a Ouinhi (Benin). Des alevins de C. gariepinus (6,74 ± 0,27 g) et de O. niloticus (8,11 ± 0,14 g) ont ete places respectivement dans des happas de 1 m 2 (30 alevins / m 2 ) et de 6,25 m 2 (30 alevins / happa), les happas contenant C. gariepinus etant inseres dans les happas contenant O. niloticus . Trois types d’aliments ont ete testes: aliment importe Sckretting (45% de proteines), aliment local (37% de proteines), et aliment mixte (50% aliment local et 50% aliment importe). Seuls les alevins de C. gariepinus ont ete nourris, les alevins de O. niloticus se nourrissant de la production primaire produite par les dejections de C. gariepinus . Les meilleures performances zootechniques et d’utilisation alimentaire ont ete obtenues avec l’aliment mixte suivi de l’aliment importe chez les deux especes. Chez C. gariepinus , le poids moyen final a varie de 20,95 ± 1,12 g a 42,56 ± 2,26 g tandis que chez O. niloticus il a varie de 17,00 ± 1,84 g a 19,63 ± 0,83 g. La presente etude a clairement montre que la co-culture Clarias gariepinus – Oreochromis niloticus avec nourrissage seulement de C. gariepinus est une forme d’elevage de plusieurs especes de poissons a la fois a cout reduit.