Assessment of Tono and Vea Reservoirs for Sustainable Nile Tilapia (Oreochromis Niloticus) Cage Aquaculture Development in Upper East Region, Ghana

The use of man-made aquatic ecosystems such as reservoirs and dugouts originally built for water supply, irrigation and fish farming is an emerging trend in most developing countries. Most reservoirs are being assessed for their potential for cage fish culture as a result of the high demand of fish. Northern Ghana has a number of reservoirs and dugouts which were originally constructed to conserve water for irrigated farming particularly the Tono and Vea reservoirs, however they seem to be under-utilized. This study was conducted to evaluate the potential of cage aquaculture on the reservoirs by assessment of the water quality, suitable zones, carrying capacity (CC) and development of aquaculture management areas (AMAs) within two major reservoirs in Upper East Region (UER) namely; Tono and Vea reservoirs. These reservoirs were monitored using linear stratified sampling technique and monthly sampling of eighteen water quality variables between 06:00 to 10:00 for fifteen months (February 2015 to April 2016). Three replicates of samples were obtained for each variable from each stratum of the reservoir. Water temperature, water depth, transparency, pH and conductivity were measured in-situ using combined portable meters. Water sampling and laboratory analysis were based on standard analytical methods for examination of water and waste-water. Temporal and spatial dynamics of the reservoirs were investigated using multivariate statistical methods to obtain three seasonality regimes from the water quality with total variance in both reservoirs < 88.5%. Water quality in both reservoirs could support Nile tilapia culture (temperature between 26.730 ⁰C, dissolved oxygen > 5 mg l-1, average water depth > 3 m but < 10 m, pH was slightly acidic to slightly alkaline). Geographical information system-based spatial multi-criteria analysis results indicate that 3.85 km2 (39.05% suitability) and 2.15 km2 (68.40% suitability) of reservoir area were suitable for the development of cage aquaculture in Tono and Vea reservoirs, respectively. Estimates of carrying capacity i.e. production, physical, ecological, and social were integrated to obtain the final aquaculture CC of 719.40 m-3 and 65.55 m-3 as production volume for Tono and Vea reservoirs, respectively. Results for trophic level index (TLI) indicate that Tono reservoir has very high nutrient enriched waters (TLI: 5.23; super trophic), whiles Vea reservoir has high nutrient enriched waters (TLI: 4.32; eutrophic). Based on the trophic status, percentage allocation of aquaculture CC and other secondary data; the three AMAs in Tono reservoir and the five AMAs in Vea reservoir could produce 107.91 and 9.83 metric tonnes of cultured Nile tilapia per production cycle respectively. The study postulate that the ecosystem approach to aquaculture could be pragmatic stepwise approach that has salient potential to deal with environmental, economic and social issues associated with cage culture in Tono and Vea reservoirs. Best management practices (BMPs), physical and biosecurity measures are needed to minimise aquatic animal health risk. The use of CC based suitable zones and identification of individual AMAs are recommended as useful for decision-making by fisheries and aquaculture regulators, managers of reservoirs and other aquaculture policy-makers for sustainable cage aquaculture in the two reservoirs.

Source: KNUST