Summary
From August 6-17, 1990, an environmental assessment was conducted at 10 potential sites (in seven prefectures) for cooperatively managed, integrated aquaculture farms in the marais (wetland valleys) of Rwanda. Sites were evaluated for existing pond construction and management practices and recommendations were made to minimize the risk of water borne diseases and other negative environmental impacts.
Snail hosts for schistosomiasis and seep and cattle liver fluke occurred at more than half of the 10 ponds sampled. Mosquito larvae were less common, and anopheline mosquitoes (vectors of malaria) were found at only one site. Most snails and mosquitoes occurred at poorly built and managed ponds. Most snails and mosquitoes occurred at poorly built and managed ponds. The presence of a well-trained extension agent at a site was a critical factor to ensure well-managed ponds and thus reduce risk of waterborne disease.
Two supply canals and three discharge canals were sampled for macroinvertebrates to determine possible downstream impacts of fish ponds. Benthic communities were characterized by low biodiversity and high tolerance to organic enrichment, probably because of frequent dredging of canals, intermittent water flows, and organic runoff from human and livestock activity. No negative environmental impact directly attributable to fish culture activity was detected.
At the scale and management intensity of the proposed aquaculture centers, fishponds would have relatively low volume and infrequent discharges that should not cause undue environmental degradation downstream.
Four streams with a wide range of organic pollution were sampled for macroinvertebrates to evaluate methods for biomonitoring program. Use of a biotic index proved appropriate and practical for assessing stream water quality in Rwanda. Protocols with field methods, data interpretation tables and a cumulative list of macroinvertebrate taxa in Rwanda are provided.
Risks of indiscriminate introduction of non-native species to Rwanda are discussed, and a review and decision model for evaluating proposed exotic fish introductions is presented.