Introduction
When referring to aquaculture and environmental issues it is very important to classify types of aquaculture. We refer to extensive, semi-intensive, and intensive aquaculture and culture-based fisheries. In terms of sustainable and environmentally sound development, however, it is fundamental for these classifications.
Rural Aquaculture
Rural freshwater aquaculture in developing countries is not normally a source of environmental pollution but may have some negative impacts; for example, the spread of exotic fish species and consequent effects on native species and habitats, loss of genetic diversity, the spread of fish diseases, and public health problems due to unsafe produce, poor working conditions, waterborne diseases, and parasites.
Rural aquaculture must be considered as an additional component of agriculture and should therefore benefit from the wider experience accumulated in this field. Special efforts must be made in the identification of the potential target groups in aquaculture: development projects, as well as in the appraisal of the socioeconomic characteristics. Project formulation based on wrong assumptions about social, economic, and political factors is the primary cause of failures. The main reason for the high desertion rate has been established to be the lack of motivation in farmers due to poor returns with no surplus to commarginalize. It is only in very specific cases.
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Aquaculture in Reservoirs and Lakes
Freshwater aquaculture in lakes and reservoirs can have all the above-mentioned negative impacts, including gastro phonation through the organic fallout from fish cages, impairment of esthetic qualities, and disruption of resident fish stocks. The main constraint to the development of this sector is the lack of fisheries management plans for reservoirs. For example, in Venezuela, “the management of these water bodies constitutes a conflict area among different government organizations which share legal competence” (translated from Nova, in press). Moreover., many such water bodies do not have even the minimum required infrastructure true for exploitation and management of their fisheries, and physical and biological limitations prevent, in many cases, any development me~:t. Very often, long distances to markets and a lack of functional roads discourage attempts to develop activities. Despite these limitations, culture-based fisheries in reservoirs and lakes have significant potential, especially in regions such as Latin America. This potential has been only partially realized but affords examples of successful experiences of relevance to other parts of the world.
Intensive Freshwater Aquaculture
F developing countries are largely aimed at export markets, although tourism-related consumption may generate some seasonal demand. Intensive freshwater aquaculture in many developing countries is only just starting to expand; for example, trout and smolt production in salmon culture (Oncorhynchus mykiss, Kisutch, 0. Tschawytscha, 0. Masou, Salmo salar) in Chile (Munro 1990) and tilapia culture (0reoch.promise aureus x 0. Hornorurn) in costarica (Martinez-Palacios et al. 1989), grass carp (Ctenophore godson Della) and eel (Anguilla japonica) in China (FA0 1983), snakehead (China striates), walking catfish (Claires spp.) And giant freshwater prawn (Macro racier Rosenberger)in Thailand (Bonier attain and Akiyama 1989).
Last word
The freshwater environment can be affected by the release from fish farms of uneaten food; feces and dissolved excretory products; high microbial loads, Parasites, disease organisms, and vectors; and aquaculture chemicals, such as anesthetics, disinfectants, biocides, food additives, drugs for disease prophylaxis’ treatment and inorganic and organic fartoilers. The chemistry of the recipient water bodies and their bottom sediments can be changed by an increase in suspended solids, by biochemical and chemical oxygen demands, and by increased nutrient loading, particularly nitrogen and phosphorus. Thus, quantitative and qualitative changes in the biota (bacteria, protozoa, plankton, benthos, and fish) of recipient water bodies are very likely. Nutrient and organic enrichment may lead to local atrophy action and hypoxia or anoxia (see also Beverage 19841, although the fertilization of some obligor orphic waters may increase fish production. Wild fish populations may be threatened by diseases and parasites emanating from high levels of infection in aquaculture installations.
