Seasonal effects of the water quality in ponds on nutritive potential and digestibility of tilapia Oreochromis niloticus in natural feeding condition (Mali, West Africa)

Abstract

The effects of the water quality on food and nutritional characteristics of stomach contents of Oreochromis niloticus in semi-intensive aquaculture ponds were investigated in dry and rainy seasons. Nutrient concentrations mainly ammonium and orthophosphates in water presented significant seasonal variation. The chemical composition of the total suspended solids, the main trophic source in pond is characterized by a high proportion of mineral (89%) during the two seasons. This is reflected in the low quality of food ingested by fish: the indigestible materials (fiber and minerals) represented 70 and 61% of the diet in the dry and rainy season, respectively. Seasonal variation was not observed in the digestibility of the dietary organic matters (ash free dry matters, AFDW) and total amino acids (TAA). Analysis of these results showed that anthropogenic factors, including fertilizer application and changes in environmental conditions have affected enormously the quality of fish food and the productivity of these ponds. Key words: Seasonal changes, water quality, semi-intensive aquaculture, Nile tilapia, food quality, Mali.