No abstract

In this paper, we assess the growth performance, survival rate and abiotic factors affecting Etheria elliptica (Mollusca: Bivalvia: Etheriidae), the African freshwater oyster, a species that is widespread in tropical Africa where it is widely harvested for food and as a commodity. We collected wild oysters from the Pendjari River (Benin) and grouped them into small (23.4 ± 5.2 mm) and large (55.8 ± 7.7 mm) size classes. They were reared in cages in the Pendjari River from January to December 2009. Shell height was measured on a monthly basis, and estimated growth parameters were assessed using the von Bertalanffy growth function. Overall, the growth parameter estimates for pooled size classes were K = 0.0718 month À1 and L ∞ = 82.2 mm. We estimated the time to reach minimum commercial size T 65mm (female sexual maturity size) to be 22 months (1.8 years). Small oysters exhibited a peak in growth rate (2.775 mm month À1) in May, whereas large-sized oysters grew fastest (1.707-2.781 mm month À1) in August-September during the rainy/ flood season. Survival of small-sized oysters declined sharply from May (60%) to June (11%) at the onset of the rainy season, six months after the beginning of experiment, while large oysters had higher survival in June (79.2%), which decreased in December (26.4%). Among abiotic factors investigated, water transparency was negatively correlated with the growth increment of small-sized oysters (p < 0.05). E. elliptica is a suitable candidate for culture due to its large maximum size, reasonable growth rate, and wide geographic range.

T HE STUDY aims at evaluating the quality of the water in the Ouémé River basin. Data were collected from October 2014 through September 2015. Physico-chemical parameters were assessed and the concentrations of dissolved heavy metals were determined. The results show both physical and chemical pollutions of the water according to a nonlinear pollution gradient. The middle basin up to the height of the city of Kaboua appears to be the most polluted segment. The Delta region, near the coast, is the second most polluted segment, and the remaining parts of the basin are the least polluted. Pollutant concentrations are highest during the low flow season. Cluster analysis and Principal Component Analysis (PCA) of sampled sites reveals that Atchakpa-Rejet and Kaboua have high concentrations of nitrite, nitrate, ammonium, orthophosphate, conductivity, TDS, pH, calcium, magnesium, and total hardness. Kpassa, Bétérou, and Atchakpa-Bethel have high dissolved oxygen and high transparency values. All other sites have high alkalinity. During the low flow season, Cd, Pb, Zn and Cu were detected at concentrations exceeding ecological standards in most of the sites. The Water Quality Index (WQI) ranged from 52.7 to 80.9, meaning that water in that river basin can be classified either as marginal quality, moderately polluted, or good quality for aquatic life. Overall, water in the Oueme River basin is under high and increasing influence of human activities.

No abstract

This study is the first of its kind on the population of Lates niloticus from the Pendjari River (West Africa). It provides information on length frequency distributions, length-length, weight-length relationships and condition factor of the species. A total of 781 specimens were used for this study and were caught by artisanal fishing gears between Februay 2006 and January 2007. The length frequency distributions were unimodal. Individuals larger than 20.0 -22.5 cm (modal class) were more abundant (71.06 %). Monthly, the coefficient b and the condition factor (K) ranged from 2.83 to 3.31 (mean = 3.14) and from 0.44 to 2.44 (1.14), respectively. The growth was in favour of the body weight (b>3, positive allometric growth) during the low water season and in favour of the length (b<3, negative allometric growth) during the high water season. Whenever possible, the b values for the species obtained both in this study and in some of the previously reported ones were compared. Generally, b values indicate a positive allometric growth for the species.

No abstract

No abstract

No abstract