Effects of Cage Culture of Nile Tilapia (Oreochromis niloticus) On Water Quality of the Volta Lake at Ardec (Akosombo) And Fresh Volta Tilapia Farms (Akwamufie) In the Assuogyaman District of Ghana

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JUNE, 2015
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The determination of cage culture effects of Oreochromis niloticus on water quality in terms of depth and distance was investigated from June 2013 to September 2014. Three sampling points namely ARDEC, Volta Fresh Tilapia farm and a point where there is no farm (no cage) were selected for sampling. Sampling was carried out in cage and 50 m and 10 m both upstream and downstream away from the edge of the cage. In terms of depth, sampling was carried out at the surface and 5 m below the surface of the cage. A total number of two hundred and fifty-two (252) water samples including forty-two (42) samples on monthly basis were collected for a period of six (6) months (March to August) and were analysed for temperature, total dissolved solids, total suspended solids, turbidity, pH, dissolved oxygen, biological oxygen demand, ammonia, nitrate and phosphorous. Results revealed that at surface, both cultures recorded high temperatures as compared to control while control bottom recorded high temperature as compared to cage bottom for ARDEC and Fresh Volta Tilapia, Akwamufie. The minimum and maximum range of values of pH for both ARDEC and Akwamufie (SK2 and SK6) significantly fall within 6.41 – 6.85. ARDEC and Akwamufie in respect of pH has values of 6.88 and 6.85 respectively which was also significant in respect of the control stations pairing a pH value of 6.41(P<0.005) (SK7). DO increases along distances 10m and 50m upstream and downstream with respect to ARDEC at control side and rather decreases at cage side whilst Akwamufie decreases at control side and increases at cage side. The study found slight variation in the cage surface and bottom with respect to ARDEC and Akwamufie though both sites were significantly different from control. The control surface and control bottom had a considerably less or low suspended matter at both culture stations as compared to ARDEC and Akwamufie. There was variation in conductivity, turbidity and BOD at cage side and control. The indicator variables for TDS appeared to be similar with the depth of the cage bottom being the most highest among the culture stations. The NO3-N level at the control surface was lower than the cage surface whereas the NO3-N with respect to the culture depth was also lower at the control bottom than the cage bottom. The NH3-N at cage side was twice that of the control side. The PO4– P content increases sharply with respect to the depth of the water with variations at ARDEC and Akwamufie stations at the cage surface and bottom recording 0.12 and 0.14mg/1 at ARDEC and 0.13 and 0.18mg/1 at Akwamufie respectively but both significantly higher than control. These significant changes in parameters as compared to control could affect water quality leading to total degradation on these sites if not checked.
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A thesis submitted to the Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements of Master of Science degree in Environmental Science,
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