Food production invariably has environmental effects: occupation and fragmentation of former natural habitats; reduction of the abundance and diversity of wildlife; and changes in soil, water and landscape quality. Most integrated agriculture-aquaculture (IAA) systems use low levels of inputs and fall within the type of aquaculture called semi-intensive. This means less reliance on heavy feed and fertilized inputs, lower densities of farmed organisms and, therefore, less chances of causing serious pollution and disease risks than more intensive, feedlot-type systems. This is important as it is the high output of the foodstuffs necessary for intensive feedlot systems that create environmental pollution. Semi-intensive systems in synergy with agriculture (crop- livestock-fish integrated farming) capitalize on in situ, vitamin and protein natural aquatic feeds, which obviate the need for expensive feed components.
Semi-intensive freshwater ponds usually have few environmental effects other than their occupation of former natural habitats. In the tropics, where there is fast turnover of organic waste loading, their effluents and excavated muds usually enhance the productivity of adjacent waters and lands and avoid overenrichment.
Special care is needed, however, where pond and dike construction may disturb acid sulphate subsoils and where water table changes may uplift subsurface salts. Moreover, saltwater intrusion from coastal ponds may poison soils and freshwater aquifers. The use of chemicals in semi-intensive aquaculture is usually limited, but farmers should always take great care when using antibiotics, hormones and other drugs and should follow the instructions very closely. Seek professional advice from a veterinarian or fish culture specialist and be aware that many drugs are persistent in the environment.
The aquatic medium is shared by many users and supports a diverse fauna and flora. As aquaculturists develop better domesticated breeds, international demand for these will increase. This means increased transfers of exotic breeds, as has been of immense benefit for crop and livestock farming. However, cultured aquatic organisms often escape and form feral populations which may: (1) displace or interbreed with wild stocks, thereby threatening natural genetic resources; (2) disrupt natural habitats by causing proliferation or clearance of vegetation or increasing turbidity (benthic foraging); and (3) introduce aquatic pathogens, predators and pests inadvertently.
Development agencies and farmers must weigh the benefits of using exotic breeds against possible environmental consequences. Development projects and farmers often try exotic breeds without thorough appraisal of the possible consequences. Such irresponsible experiments may have far-reaching consequences; loss or damage to habitats and genetic resources of wide importance. This damage may last forever. Codes of practice to avoid this have recently been developed, but aquaculture development still lags behind agriculture in recognition of the risks of transfers and international application of these safeguards.
The only general guidelines here are: (1) use native species and breeds developed by local or national programs wherever possible; and (2) if the introduction of other species or breeds needs to be considered, seek professional advice on how to assess the possible consequences and comply with the laws and Codes of Practice that have been developed for the good of all present and future farmers.
IAA generally has no special health risks significantly greater than agriculture, but freshwater ponds may assist the spread of waterborne diseases. They can harbour the intermediate hosts of parasitic worms, such as bilharzia, and can be breeding sites for mosquitoes. Such problems are minimized by maintaining weed-free, well-stocked ponds. In fact, many species of fish eat and control mosquito larva but snail control by fish is not usually possible.
Fish farm workers who enter ponds may risk bilharzia infection in infected areas and other waterborne microbial diseases (viral, leptospiral, bacterial and fungal).
On the positive side, many of the pathogens and parasites that contaminate fish produced from livestock excreta-fed ponds are eliminated by a well-fertilized pond environment, as in sewage oxidation ponds. Problems of pesticide accumulation in ricefield fish are diminishing because of the increased use of integrated pest management programs employing natural substances and predators.
The risk of accumulation of heavy metals from livestock feeds in manured pond sediments and fish is slight and applies more to intensive systems. The same probably applies to pathways for aflatoxins (poisons that develop from fungi in badly stored feeds) but this has been little studied.
Sewage-fish culture is controversial because of assumed health risks to farm workers and fish consumers. However, these may be slight compared to the nutritional benefits provided that postharvest handling of the fish is hygienic (with particular attention to not rupturing the gut and allowing its contents to make contact with fish flesh). Such produce must also be well-cooked.
There are no general guidelines on how to minimize these risks other than to be aware of which waterborne diseases are present in any given locality and to assess whether the establishment and operation of ponds significantly adds to the risks of contraction by farm workers, fish handlers and consumers.
Seek professional advice from public health workers.
Issues for further consideration
Integration of farming activities through recycling is a traditional practice in many societies in Asia, where these have evolved beyond slash-and-burn cultivation. On the other hand, the integration of aquaculture into these traditional farms was and still is not widely practiced, counter to common perception. It originated in China and was spread throughout many parts of Asia by Chinese migrants, but often remained a practice common only to these groups.
The multiple-use aspect of ponds and their benefits to other enterprises of the farm, notably vegetables and livestock, is characteristic. Here, the impacts of semi-intensive ponds on the environment, through conservation of surrounding habitats and species, may be positive. The conversion of low-lying areas to perennial ponds can benefit surrounding natural habitats and organisms by increasing the availability of water.
Snail control may be one of the benefits of integrating fish culture closely within the farming system. Ducks allowed to forage in paddy fields and fishponds can control snails, as well as other pests. If done correctly, catfish and common carp stocked in ponds and ricefields will keep golden apple snail damage below economically damaging thresholds.
Taking a different perspective, the impacts of the environment on the potential and practice of IAA should be considered. For example, the potential for IAA may be high in peri-urban areas, but with high prevalence of pollution from industry and households, increasing competition for water and land at increasing prices, high rates of city expansions covering agricultural land, the probability for sustained success of such activities is low.