Search

Sex control in tilapia should provide an invaluable benefit to aquaculture. The effects of different dietary levels of papaya carica seed meal powder on growth and gonad histology in Oreochromis niloticus larvae were studied to prevent early maturity and uncontrolled spawning. Four (4) dietary level of seed meal powder, varying from 0 g.Kg–1 as a control; 1 g.Kg–1; 2 g.Kg–1 to 3 g.Kg–1 were each tested in triplicate. The diet were isonitrogenous and were fed to twelve (12) experimental groups of 110 larvae weighing 0.019 g at a feeding rate of 4% body weight, three times a day for 30 days with the experimental diet and then after fed with the basal diet for other 60 days of the experiment. At the end of the experiment, 24 fish from all replicates were randomly sampled, slaughtered and dissected to remove testicles and ovaries. Testicular and ovarian sampleswere fixed in 10% buffered formalin for 24 h before the histological process. After 90 days of experiment, fish weight increased from 0.019 g ± 0.09 to 32.47g ± 0.02; 30.40g ± 0.05; 34.68 g ± 0.07 and 33.83 g ± 0.09 respectively for C. papaya dosage of 0; 1; 2 and 3, respectively. In fish treated with 0 and 1 g.Kg-1 of PSM, the testes showed different stages of spermatogenesis with germ cells moving up to the spermatozoa. Similarly, the ovaries showed follicles at different stages of folliculogenesis up to vitellogenesis. The main lesional changes observed concerned the testicles of fish fed with 2 and 3 g.Kg-1 PSM with in particular the scarcity of germ cells and spermatozoa. For females, the only observations concern vitellogenesis which are important for treatment doses of 0 and 1 g.Kg-1, while they decrease in the group treated with 3 g.Kg-1.© 2019 International Formulae Group. All rights reservedKeywords: Papaya seed meal powder, Performances, Gonads histology, Oreochromis niloticus

International audience; A comparative study, combining three different assessment methods (fish gillnet sampling, artisanal fisheries surveys and hydroacoustics) was conducted in Mali where two man-made reservoirs (Sélingué and Manantali) are particularly suited for investigating the impact of fishing effort on the fish assemblage. These two ecosystems have relatively similar areas, edaphic and environmental properties but are subjected to different levels of fishing exploitation (low at Manantali, high at Sélingué). The comparison is based on two indicator parameters: the abundance indices and the size spectra distributions, obtained by the three methods at two contrasting hydrological seasons (April and October). The results were compared first between the two seasons, and then between the two lakes. The present work is based on two main hypotheses: (1) that there is a higher fish abundance in October associated with smaller overall sizes, after spawning; (2) a lower abundance and smaller sizes in the Sélingué reservoir than in Manantali, because of the much higher fishing pressure in Sélingué. The relevance of each method to the selected indicators is discussed. On the one hand, the three methodologies on the whole gave similar conclusions and they also complement each other. On the other hand, some results do not match the hypotheses because of biases due to difficulties and technical limitations of each method in such ecosystems (shallow water with vegetation and stumps of former forests)