ASSESSMENT OF TONO AND VEA RESERVOIRS FOR SUSTAINABLE NILE TILAPIA (Oreochromis niloticus) CAGE AQUACULTURE DEVELOPMENT IN UPPER EAST REGION, GHANA
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Date
2019-06
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KNUST
Abstract
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 tones 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 minimize 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.
Description
A thesis submitted to the Department of Fisheries and Watershed Management,
College of Agriculture and Natural Resources, Kumasi in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY IN AQUACULTURE AND ENVIRONMENT