水産養殖研究開発ジャーナル

概要

Trophic Status and Development of Aquaculture Management Areas (AMAs) For the two Major Reservoirs: Tono and Vea, in the Upper East Region of Ghana

Etornyo Agbeko, Daniel Adjei-Boateng, Nelson W Agbo and Thomas K Agyemang

Background: The development of aquaculture management areas (AMAs) is opined as one of the strategies to ensure sustainable  aquaculture. AMAs allows collaborative management of individual fish farms in a coordinated manner within a demarked space, where water resources and aquaculture impacts are shared in an environmentally harmonised way. This study seeks to evaluate the trophic status and develop potential AMAs for the Tono and Vea reservoirs in the Upper East Region of Ghana.
Materials and Methods: Reservoir water depth, transparency, chlorophyll-a, nitrate-nitrogen, nitrite-nitrogen, ammonium-nitrogen and phosphorus concentrations was monitored for 15 months (February 2015-April 2016). The trophic status of the water was estimated from the concentrations of the water quality parameters after laboratory analysis. The composite values obtained were integrated into a tropic level index (TLI) equation and values compared to standard nutrient enrichment categories. The AMAs were demarcated from suitable zones within the reservoirs based on percentage allocation of the reservoirs’ aquaculture carrying capacity and other factors peculiar to each reservoir.
Results: The trophic level index (TLI) showed that the Tono reservoir is super trophic (TLI: 5.23) indicating very high nutrient enrichment category, whiles the Vea Reservoir is eutrophic (TLI: 4.32) indicating high nutrient enrichment. Three potential AMAs were generated for the Tono reservoir and five AMAs for Vea reservoir, with allowable daily feed loading of 388.48 and 35.40 kg, respectively. These AMAs can produce a maximum of 107.91 and 9.83 metric tonnes of fish per production cycle in a year in Tono and Vea reservoirs, respectively.
Conclusion: The high trophic status in both reservoirs could be bio-manipulated by culturing filter-feeding planktivorous fish such as Nile tilapia. AMAs identified should be backed with policies and strategies for implementation of maximum fish production on quota basis, coupled with regular water quality monitoring programmes and continuous stakeholder engagement and participation.