Ponds culture of juveniles of freshwater oyster Etheria elliptica Lamarck, 1807 in Benin (West Africa)

Abstract

In order to domesticate the freshwater oyster Etheria elliptica, a 42-day freshwater pond rearing trial was conducted in two ponds of equal size (12 m 2 x 1.10 m deep), one of which was fertilized with poultry droppings and the other one was a control (unfertilized). Three depths (30 cm, 60 cm, 90 cm from the bottom of the pond) were tested with one repetition. For each depth, 02 sieves (40 cm diameter and 15 cm depth) were used. A total of 180 oysters with an average size of 37.56±1.95 mm and an initial average weight of 30.35±0.72 g were used with a density of 15 oysters per colander. pH, temperature, transparency, and phytoplankton density were measured daily between 7:00 am and 8:00 am in June-July 2018. Each week, the colanders were checked. Oysters were counted, measured and weighed. The physico-chemical parameters measured in the ponds were consistent with the requirements of tropical water oysters. At the end of the experiments, the survival rate (50±35.36%) was identical for all depths in both ponds. The best growth in size was recorded in the fertilized pond. The sizes increased 2.06 mm and 3.8 mm at 90 cm and 30 cm depth respectively). In contrast, the smallest increases were obtained in the control pond, 0.93 mm and 1 mm at 90 cm and 30 cm depth respectively. In the fertilized pond, the average daily gain ranged from 0.017 g/d (at 90 cm depth) to 0.027 g/d (at 30 cm) while it was between 0.005 g/d (90 cm) and 0.017 g/d (30 cm) in the control pond. As for the specific growth rate, it varied from 0.014%.d -1 (90 cm) to 0.047%.d -1 (30 cm) in the control pond while it was between 0.047%.d -1 (90 cm) and 0.078%.d -1 (30 cm) in the fertilized pond. The best zootechnical performance was recorded between 30 cm and 60 cm in both ponds. Therefore, depths between 30 cm and 60 cm seem to be suitable for rearing Etheria elliptica in ponds. Also, fertilization of the rearing ponds with poultry droppings would improve the growth of the reared oysters.