Demographic parameters and exploitation rate of five key fishes of Okpara Stream, Oueme River, Benin, West Africa

The current study was carried out on Okpara Stream in Northern Benin to evaluate the demographic factors with inferences on fisheries status of five dominant fish species, which were sampled monthly intervals for 18 months. Asymptotic length (L∞) ranged from 36.23 cm (Brycinus macrolepidotus) to 18.8 cm (Hemichromis fasciatus). Growth rates (K) varied between 1.6 yr-1 and 0.66 yr-1 with growth performance index (Φ’) ranging from 2.4 to 3.1. Theoretical age at length zero (t0) varied -0.95 year for Marcusenius senegalensis to -0.59 year for Shilbe intermedius. Except for B. macolepidotus, total mortalities were higher than 2 year-1 and length at first capture (L50) ranged 7.72-12.09 cm. Marcusenius senegalensis and S. intermedius showed one annual peak of recruitment, whereas H. fasciatus, Oreochromis niloticus and B. macrolepidotus displayed two peaks. The results indicated that the stocks of these five species were underexploited. However, the low length at first capture (L50) recorded for some species, requires the implementation of early fisheries management scheme to assure a sustainable exploitation of these fishes

Food habits, ecomorphological patterns and niche breadth of the squeaker, Synodontis schall (Pisces: Siluriformes: Mochokidae) from Niger River in Northern Benin

 The squeaker, Synodontis schall dominates the Mochokid fish sub-community in Niger River in Northern Benin and shows a great economic and commercial importance. The diet of S. schall has been analysed to evaluate the food habit and resource utilization in this regional River. Fish samplings were made monthly from February 2015 to July 2016 using unbaited longlines and traps, seines and experimental gillnets. The results indicated that S. schall is an omnivore foraging in benthic and pelagic habitats with diet dominated by aquatic insects (34.32%), sand particles (18.768%), macrophytes (13.415%), seeds (8.549%), roots (8.319%), detritus (5.344%), mollusks (1.204%) and phytoplankton (0.6255%). The omnivore food habit depicted was also shown by the ecomorphological analysis mainly the relative gut length (GL/SL) varying between 0.8 and 5. The species showed high diet flexibility with high niche breadth ranging between 1.86 and 5.74. Synodontis schall exhibited an ontogenetic diet shift that was also confirmed by Pianka’s diet overlap indexes ranging between Øjk=0.54-0.93. The conservation and the sustainable fisheries exploitation of S. schall require the reinforcement of fishing regulation, habitat protection and ecosystem follow-up. 

Fishery ecological survey of natural coastal lakes of Benin, West Africa

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references.Issued also on microfiche from Lange Micrographics.Fish assemblages were sampled and water physicochemistry was evaluated in Lake Nokoue and Lagoon Toho-Todougba in southern Benin. Various biological parameters (species richness, species diversity, abundance, relative abundance, ponderal indexes) were evaluated and regressed against environmental conditions to examine patterns of association. Feeding ecology and morphological diversification of the fish assemblages were examined. Multivariate procedures (principal components analysis, euclidean distance, cluster analysis, and canonical correlation analysis) were performed to examine trophic guilds and associations between trophic specialization and morphology. Fish species trophic relationships (food webs) were examined for each fish assemblage. The two fish-, assemblages exhibited low similarity in species composition due to differences in water physicochemical conditions. Among the 35 and 21 species found in Lake Nokoue and Lagoon Toho-Todougba respectively, only a few species dominated. Lake Nokoue was dominated by the perciform Gerres melanopterus and the clupeiform Ethmalosafimbriata, whereas Lagoon Toho-Todougba was dominated by the characiforyn Brycinus longipinis. In Lake Nokoue, the Akadja habitat exhibited high species richness compared to the other local biotas. In general, for the dominant species, small individuals were associated with shallow habitats with or without vegetation. Within assemblages, there was a lack of association between physicochemical conditions and community attributes. In Lagoon Toho-Todougba, the utilization of vegetation (flowers, duckweed, seeds) and aquatic insects was common, but these items were very rare in Lake Nokoue fish diets. Most likely, the destruction of the mangroves in Lake Nokoue has reduced the availability of vegetation and aquatic insects. As a result, Lagoon Toho-Todougba was dominated by detritivorous and insectivorous species, whereas Lake Nokoue was dominated by piscivorous species. About thirteen (I 3) trophic guilds were identified within both assemblages. The detritivore and the piscivore guilds contained more species than the others. Despite the differences in species composition, the two fish assemblages had similar mean values for most morphological traits, so that morphological-based centroids were similar in multivariate analyses. Most species belonging to the same feeding guild had similar morphologies indicating that a degree of diet specialization has accompanied morphological diversification. Further investigation is needed, both spatially and temporally, to assess the existing fish resources, their exploitation, and habitat associations. Also, more data are needed to better understand the roles of interspecific and intraspecific interactions and the overall pattern of community organization with regard to habitat utilization and resource partitioning. In any case, restoration of these ecosystems will require assessments of ecosystem integrity in order to diagnose the relative impacts of human activities

Partial replacement of fish meal with Azola meal in diets for Nile tilapia (Oreochromis niloticus L.) affects growth and whole body fatty acid composition

The replacement of fishmeal (FM) with Azolla meal (AM) in diets on growth and fatty acid in Nile tilapia, Oreochromis niloticus (initial mean weight: 16.4 g) was studied. Fish were fed with six isonitrogenous (29.2% CP) and isoenergetic (16.9 kJ.g-1) diets containing 0%, 10%, 20%, 30%, 40% and 50% AM respectively, as partial FM substitute. Diet A0 acted as a control. The final weight (51.0-88.3 g), the weight gain (210.8-438.3%) and the SGR (1.3-1.9%day-1) decreased when AM level higher than 10% in diets (P < 0.05). The FCR (1.44 to 2.35) significantly increased when AM level exceeded 20% (P < 0.05). The protein efficiency ratio and the apparent net protein utilization decreased consequently. The fatty acids in the whole fish were significantly influenced by the diets. The replacement of FM by AM produced fish with lower (n-3) highly unsaturated fatty acids mainly docosahexaenoic acid, and higher arachidonic acid (P < 0.05). The n-3/n- 6 fatty acid ratio ranged from 0.08 to 0.17, and was lower in fish fed A40 and A50 (P < 0.05). The findings suggest that high AM in diets affects Nile tilapia growth and the fern could be incorporated in diets up to 30% without any adverse effect on fish fatty acid composition. However, alternative additional source of lipid must be used to improve the quality of fish fed AM-diets