Ecological studies on the Nile tilapia: Oreochromis niloticus cultured in different aquatic habitats

Abstract

The aquatic habitat with its water quality is considered the main factor controlling the state of health and disease in both cultured and wild fish. In the present investigation the effect of water quality on the quality of the Nile tilapia, Oreochromis niloticus, has been studied. For that purpose the fish were collected from three different aquatic habitats: the River Nile in the vicinity of Cairo at 15 km downstream north of the industrial zone of Helwan, El-Abbassa freshwater fish farm and the brackish water farm at El• Fayoum. Physico-chemical characteristics of water collected from the different water bodies showed highly significant differences in the dissolved oxygen, pH, salinity, total hardness, total alkalinity, electric conductivity, total phosphorus and nitrate with the highest values in water collected from EI-Fayoum brackish water Farm, except for the dissolved oxygen which was slightly higher in the River Nile than that of the farms. Moreover, concentrations of the heavy metals (Fe, Cu, Zn and Mn) were significantly higher in water collected from both fish farms than that collected from the River Nile, except for zinc which was higher in water collected from the River Nile. Phytoplankton showed the highest density in the freshwater farm at El-Abbassa and the highest zooplankton density was recorded in the brackish water farm at El-Fayoum. However, water collected from the River Nile in the vicinity of Cairo showed much lower density of both phyto and zooplankton. Fish collected from the River Nile had lower values of the red blood cell count, haemoglobin content, packed cell volume and serum total lipids but higher white blood cell count and serum; glucose, total protein, AST, ALT, creatinine and uric acid than fish collected from both farms. This indicated that Nile tilapia from the farms are superior in quality compared with those from the River Nile. Bioaccumulation of either of the studied heavy metals in gills, liver, kidneys and muscles of fish collected from the River Nile was much higher than that of fish collected from EI-Abbassa and El- Fayoum farms respectively and led to clear damage in tissues of those vital organs. The results also revealed that the meat quality of fish collected from El-Fayoum Farm was more superior than that of fish collected from El Abbassa Fann and the River Nile which appeared of lower quality.