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The study on integration of tilapia and vegetable cultivation was conducted at Silkamba, in west shoa zone, Ethiopia. The Nile tilapia fingerlings were stocked (3/m 2) in an earthen pond fertilized with cow dung and poultry excreta at 3:1 ratio. A control pond was maintained without fertilization. The seedlings of the tomato (Cochoro variety) and onion (Bombay red) were planted on twelve plots prepared adjacent to the ponds. The seedlings on six treatment plots were grown by addition of the fertilized fish pond water and control plants were supplied with the control pond water. Physico-chemical parameters like dissolved oxygen, pH, carbon dioxide, alkalinity and nitrate in the treatment pond remained within the required level for the growth of Nile tilapia. The water temperature was comparatively high which was more suitable for the production of fish food organisms as well as the fish growth in the pond. The level of nitrate and total phosphorus in the treatment pond was at the suitable level which enhanced the growth of plankton and benthic organisms in the pond. The bottom soil in the treatment pond showed comparatively high level of organic carbon and organic matter than the control pond. The number of tomato fruit and their size were higher in the treatment plots. Similarly the yield of onion from the treatment plots was higher than the control plot. The total yield of fish from the treatment was 27.22kg. The results on the analysis of expenditure and income indicated that the integration of vegetable cultivation using fish pond water alone was more profitable than the conventional method of vegetable cultivation with the application of fertilizer.

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Studies were conducted to assess the impact of Biocenosis on water quality parameters like temperature, pH, conductivity, total alkalinity, chloride, dissolved oxygen and carbon dioxide in the sewage oxidation ponds at Ambo University campus, Ethiopia. The phytoplankton of 10 genera belonging to Chlorophyceae, Bacillariophyceae, Euglenoideae and Cyanophyceae as well as zooplankton such as rotifers, ostracods and copepods were observed. The major benthic fauna recorded were seven genera of insects and a single genus of oligochaete and nematode respectively. Three dominant bacterial genera namely Enterobacter sp, E-coli and Pseudomonas sp. were isolated from the water. In McConkey agar medium the mean density of the bacterial population was found to be 27 x10 3 , 29 x10 3 and 6 x10 3 in the three ponds respectively. Whereas, in the Pseudomonas agar they were found to be 79 x10 3 , 74x10 3 and 107x10 3 respectively in ponds 1, 2 and 3. However, in the nutrient agar, the bacterial colonies were moderate in numbers and the mean values were 22 x10 3 , 37 x10 3 and 17x10 3 in pond 1, 2 and 3 respectively. The results on the physico-chemical parameters indicated that the alkaline pH and high dissolved oxygen in the second and third oxidation ponds were within the permissible level for fish culture. Further, the results on the phytoplankton also revealed the high photosynthetic activity which enhances oxygen content and production of live food organisms.