Growth of freshwater Etheria elliptica oyster (Lamarck, 1807) reared in cages in the Pendjari River (Benin, West Africa)

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 (-1) and L-infinity = 82.2 mm. We estimated the time to reach minimum commercial size T65mm (female sexual maturity size) to be 22 months (1.8 years). Small oysters exhibited a peak in growth rate (2.775mmmonth(-1)) in May, whereas large-sized oysters grew fastest (1.707-2.781mmmonth(-1)) 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.