Effects of weaning age on survival and growth factors of Heterotis niloticus (Cuvier, 1829) larvae

Heterotis niloticus is an important fishery resource because of its individual large size and high commercial value. There is population decline due to habitat degradation and high fishing effort. The rearing of H. niloticus larvae, particularly the weaning phase, is one of the major problems for the successful farming of this species. This research aimed at investigating the age at weaning of H. niloticus larvae and its effects on survival and growth rates. Two independent series of weaning experiments were conducted under natural conditions. The first experiment (early weaning stage) included four treatments, namely: T1 (control) = larvae fed only Artemia nauplii, and T2, T3, T4 corresponding to three weaning ages of 11, 13, and 15 days after hatch (DAH), respectively. The second experiment (late weaning) included three treatments: T1 (control) =larvae fed only Artemia nauplii, and T2, T3 corresponding to two weaning ages, 24 and 26 DAH, respectively. For the early weaning experiment, eight days (9 DAH -16 DAH) of larval rearing resulted in low survival (14.7%, 10.0%, and 14.1%) and low SGR (6.56%.d-1, 6.55%.d-1, and 7.68 %.d-1) for the 11 DAH, 13 DAH, and 15 DAH larvae, respectively. The survival (65.29%) and SGR (12.55%.d-1) from Artemia fed larvae were thehighest and significantly different (

Partial replacement of fish meal with Azolla 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.Keywords: Azolla, Fish meal replacement, Growth, Fatty acids, Oreochromis niloticus, bioconversio

The Mangrove Fishes in the Benin Estuarine System (Benin,West Africa) : Diversity, Degradation And Management Implications

A preliminary study of the mangrove fishes was undertaken from March 2000 to September 2001 in the Benin estuarine lagoon system in connected to the Mono river; a dam was constructed on this river to provide the Togo and Benin countries with electricity. The research aims to investigate fish species diversity and ecosystem degradation impacts in order to protect and to improve the mangrove fish resources. Specific objectives were (1) to investigate fish assemblages and distribution in the mangrove/estuarine habitat; (2) to investigate relationships between environment features and biological attributes; (3) to evaluate the estuarine ecosystem degradation, with regard to mangrove destruction and recent evolution of the Mono river caused by a dam construction, and impacts on fish population (4) to survey socioeconomic aspects of resources exploitation and (5) to initiate a resource management / conservation plan in participatory approaches. Preliminary results from wet and dry season samplings in the four habitat categories, mangrove fringe, adjacent open water, adjacent marginal vegetation and channel are as follow: The two dominant species of mangroves, Rizophora racemosa and Avicennia africana, are being intensively degraded for domestic use such as firewood. The fish assemblages was dominated by the detritivores (39.4%) and planktinovores/microcarnivores (45.6%). Overall, 51 fish species belonging to 26 families were collected. Cichlidae (5 species), Eleotridae (7 species), Mugilidae (5 species) were the most speciose families. Six (6) species, Sarotherodon melanotheron (Cichlidae), Kribia nana (Eleotridae), Gerres melanopterus (Gerreidae), Hemichromis fasciatus (Cichlidae), Ethmalosa fimbriata (Clupeidae), Aplocheilichthys spilauch en (Cyprinotontidae), dominated the sample and account for about 80%. Sarotherodon melanotheron constituted the major dominant species and account numerically for about 29% of the total catches and 46.7% of the total biomass.Unpublishe

Salinity Tolerance of Dormitator lebretonis (Pisces: Eleotridae: Steindachner, 1870) Reared in Water Tanks: Implications for Coastal Wetlands and Swamp Valorizations

Dormitator lebretonis (Eleotridae: Steindachner, 1870) is a fish species that inhabits West African coastal environments from Senegal to Angola where this squeaker appears to be an important component of the artisanal fisheries. In particular, this eleotrid is widespread in Benin coastal waters including wetlands, and is intensively exploited for food. The current rearing experiment aimed to determine the salinity levels that favor the survival and growth factors of this squeaker. Six (6) treatments corresponding to six (6) salinity levels (0‰, 5‰, 10‰, 15‰, 20‰, 25‰) and three replicates with 15 individuals of D. lebretonis per replicate were considered for the experiment. Appropriate salinity levels were obtained from a mixture of sea water and fresh water. Overall, within each six (6) treatments, physicochemical features showed insignificant (P>0.05) variations. Regardless of rearing water salinity (0‰ - 25‰), D. lebretonis displayed high survivals ranging between 86.66% (salinity: 0‰) and 100% (salinity: 5‰ - 20‰). Percent weight gained (PWG: 7.94±0.01% - 14.39±0.02%) were moderate and significantly (P<0.05) varied with treatments. Also, significant (P<0.05) variations in the condition factors (K) were recorded, with means ranging between 1.68±0.04 and 1.92±0.01. Nevertheless, specific growth rates (SGR) did not show any significant (F5,18=0.328; P=0.890) variations across treatments. These findings could serve as reference data for an extensive aquacultural valorization of D. lebretonis in numerous Benin coastal wetlands and swamps

Primary production, food web structure, and fish yields in constructed and natural wetlands in the floodplain of an African river

In the Ouémé River, Africa, whedo (artificial pond) aquaculture on the floodplain is an important method of fishery production. We surveyed fishes in whedos and adjacent main-channel and floodplain habitats during the receding-water period (December 2010 – January 2011) and analyzed carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of fish and primary producer tissue samples to investigate food web structure. We also measured instream respiration, net primary production, algal biomass (chlorophyll a), and nutrient concentrations in the habitats. Floodplain habitats were more nutrient-rich than the river channel, and whedos were net heterotrophic (net primary production &lt; 0). Phytomicrobenthos and C3 macrophytes accounted for a large fraction of fish biomass in whedos and the natural floodplain depression, while the river channel was mainly supported by seston and C3 macrophytes. Whedo food webs were dominated by piscivorous fishes and had fewer trophic transfers compared with the food web of the river channel. Our results suggest that control of aquatic macrophyte growth in whedos may yield greater algal production and consumer biomass, including harvestable fish stocks. </jats:p