Hazards refer to activities that could put the lives of individuals at risk, directly or indirectly. Hazard assessment in fish production systems is a process designed to determine whether the activities involved in fish production pose hazards of any kind.
The hazards in pond fish production may be grouped into two categories: pathogenic agent-borne hazards and non-pathogenic agent-borne hazards.
Types of Hazards in Fish Ponds
1. Pathogenic Agent-Borne Hazards in Fish Ponds
Pathogenic agent-borne hazards are those due to agents in the water or in the fish that cause infections, which can affect both fish and individuals involved in fish handling.
The pathogenic organisms like viruses, bacteria, protozoa, and parasites present in the aquatic environment are known for their potential hazard to fish and consumers. Several authors cited by Ogbondeminu (1993) reported evidence that fish can act as vectors of enteropathogenic bacteria.
Out of the 35 species of bacteria from nine genera isolated from or associated with diseased fish in various parts of the world, nine species from seven genera have been detected in association with bacterial diseases of humans.
Some of these organisms may not be pathogenic to fish but, when consumed by humans, may cause infections such as paratyphoid fever, bacillary dysentery, cholera, gastroenteritis, infectious hepatitis, and other bacterial food-poisoning conditions (Ogbondeminu, 1993).
Ibiwoye (1994) added that some of these diseases pose a potential health hazard to humans because of the risks involved in handling or eating inadequately cooked fish.
Fish, like livestock, are prone to various infections that affect their reproduction, growth, and appearance, thus impacting their wholesomeness. The treatment of fish with antimicrobial agents may pose a potential hazard to handlers and consumers.
Ogbondeminu (1993) indicated that the public health significance of fish contamination lies not only in their ability to cause disease but also in their possible role in transferring antibiotic-resistant strains with R-plasmids to other common pathogens affecting both homeothermic and poikilothermic animals.
Although there is limited information on cultured fish and their environment as probable sources of human enteropathogenic bacteria, Ogbondeminu (1994) confirmed that fish from tropical aquaculture systems can harbor a variety of gram-negative bacteria in their intestinal tracts.
He further stated that the majority of these bacteria carried in the gastrointestinal tract of fish pose a primary occupational hazard to handlers.
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Causes of Pathogenic Agent-Borne Hazards in Fish Ponds
Infectious diseases caused by bacteria, fungi, viruses, protozoa, and helminths can be accidentally transmitted to farmers through their association with the aquatic environment, handling fish, or consuming improperly cooked fish.
Ogbondeminu and Okaeme (1985) isolated 13 bacterial species associated with organic manure and water, reporting that the presence of Pseudomonas, Escherichia, Aeromonas, and Staphylococcus species is of public health significance due to their primary role in occupational diseases of fish handlers.
Out of the nine species, Aspergillus species, Mucor species, and Candida albicans have been reported to cause clinical disease in fish and shellfish, all of which are significant to public health because they can cause diseases in humans.
The presence of the Salmonella group in manure or human waste is risky because it contains several serotypes that are pathogenic to both humans and animals. It is noteworthy that pigs are known reservoirs of pathogenic Salmonella, so the use of porcine manure for pond fertilization should be done with care.
Furthermore, the occurrence of Salmonella sp. and Klebsiella pneumonia is common and is known to cause various diseases in humans (Ogbondeminu et al., 1992). This indicates that bacterial contamination of ponds poses a potential human epidemiological hazard.
The consumption and processing of fish grown in waste-fed pond systems increase the possibility of transferring parasites (e.g., Haplorchis parnillis) or pathogens to humans. Parasites embedded in the dermis or musculature of fish cause severe necrotic ulcerative granulomatosis, rendering the fish unmarketable and unacceptable to consumers (Ibiwoye et al., 1996). Protozoa (Ichthyophthirius multifiliis), cestodes, trematodes, and nematodes have also been reported.
Other parasites such as Argulus sp., Ergasilus sp., and Lernea sp. are common (Ibiwoye et al., 1996). Encysted worms throughout the muscles of fish can be zoonotic, posing risks when improperly cooked fish is consumed.
Although fish are rarely consumed raw, exposure of fish growers to infected fish and their culture water may predispose them to the transmission of potentially enteropathogenic organisms. Some of the conditions caused by infectious agents include swimmer’s itch, schistosomiasis, fascioliasis, salmonellosis, leptospirosis, aspergillosis, candidiasis, and helminthiasis.
Fish production and hazards are closely interwoven, leading Jansen (1970), cited by Ogbondeminu (1993), to postulate that the etiological agents of infections in the eyes, ears, nose, throat, gastrointestinal tract, and urinary tract in humans could be waterborne, although the sources of infection are rarely traced and should be further investigated.
Non-Pathogenic Agent-Borne Hazards in Fish Ponds
Non-pathogenic hazards are restricted to general pond management and the potential implications of chemicals.
Potential Hazards in Fish Pond Management Practices
1. Siting of a Pond
Siting is crucial when constructing a pond for fish production, as it directly impacts water quality and overall productivity. While it may seem easy to dig a hole, fill it with water, and grow fish for profit, proper management is far more complex.
Water quality management is the most important aspect of productive fish farming, requiring ongoing diligence. Daily monitoring of the pond’s condition, fish behavior, and water parameters, coupled with accurate record-keeping, is essential to prevent environmental problems and maximize production.
To avoid contamination risks, the pond should not be located where rainwater runoff flows directly into it. This runoff may carry human or animal waste, debris, and pathogenic organisms, posing significant public health risks. Michael (1988) noted that ponds should not be situated near power stations or industrial sites to prevent toxic chemical runoff from entering the pond after heavy rainfalls.
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2. Hazards Associated with Management
Fish farming, like any agricultural practice, poses potential health risks. Public health hazards include drowning, dam breaks, flood disasters, injuries from handling equipment, sunburns, and exposure to harmful gases or chemicals. Farmers may also encounter risks like stings from insects, bites from snakes and fish, and attacks from large mammals.
Pond site conditions and environmental management influence hazard exposure. Poor sanitary levels in or around the pond create environments conducive to the breeding of harmful animals like snails, toads, frogs, snakes, insects, and birds. These creatures can endanger both the fish and the people working with them. For instance, freshwater snails can carry parasites like Schistosoma species, which cause schistosomiasis in humans, entering the body through the skin (Churchill Livingstone).
Other threats include birds like herons, which not only prey on fish but also introduce parasites like the eye fluke, Diplostomum species (Edward, 1994). Snakes, both poisonous and non-poisonous, are attracted to unsanitized areas, posing a risk to farm workers and visitors. Additionally, insects such as tsetse flies can transmit diseases like sleeping sickness in humans and animals, while mosquitoes breed in stagnant, contaminated water, spreading malaria.
Leeches, which thrive in long-standing water, suck blood from both fish and humans and can serve as vectors for trypanosomiasis. Maintaining strict environmental sanitation, including water quality control, is key to minimizing these hazards.
3. Hazards Associated with Husbandry Practices
Fish farming shares many principles with livestock husbandry, including minimizing stress on the stock, maintaining a healthy environment, feeding, and disease prevention. However, handling fish can result in injuries to both farmers and fish, especially when using nets or metallic instruments. Injuries expose fish and handlers to secondary infections by parasites or bacteria.
For example, Newman (1993) reported that accidental injections during fish treatment or vaccination, due to struggling fish, can cause anaphylaxis. Such accidents pose risks to farm workers and demand careful handling of fish.
i. Personal Observations
Environmental factors also play a significant role in fish production systems. Some hazards arise from materials introduced into the water supply. Fish ponds located near residential areas often become dumping grounds for hazardous objects like broken glass, nails, or bicycle parts, which can harm farmers during harvest.
ii. General Environmental Issues
Fish spend their entire lives in water, making water quality crucial for their survival. Water, being a universal solvent, is easily contaminated by physical and chemical pollutants, which can affect fish health. Branson (1993) explained that different fish species tolerate varying levels of contamination, but the main objective is to maintain water quality within the tolerance limits of the fish.
Key water quality parameters include dissolved oxygen, carbon dioxide, chlorine, ammonia, and pH levels. Dissolved oxygen is essential for fish survival, while high carbon dioxide levels can interfere with oxygen uptake. The pH range of 6.5 to 9 is optimal for most fish species, and deviations from this range can be harmful.
4. Hazards Associated with Chemical Contaminants
Chemicals in fish ponds often originate from agricultural runoff or industrial waste. N’Daw (1991) noted that pesticide pollution is a significant concern, especially from widespread agricultural use and vector control campaigns near fish farms. Common pesticides like DDT, lindane, and endosulfan can enter aquatic environments, either directly or through land runoff.
Chemicals used in fish treatment, such as formalin, malachite green, and chloramine, can also pose risks. Edward (1993) warned that improper application of these chemicals can be toxic to fish, damaging gills and causing respiratory distress.
Management-Related Agents Causing Hazards
While Africa was once thought to be free from aquatic contamination, increased industrialization, urbanization, and land exploration have introduced a variety of pollutants into aquatic environments. Fish cultured in contaminated waters are not only more vulnerable to diseases but can also become a source of public health hazards.
Organic manure, used to fertilize ponds, can introduce microorganisms and parasites, increasing the risks of contamination. Ogbondeminu et al. (1992) recommended storing manure for at least two weeks before application to reduce coliform bacteria and other harmful pathogens.
Additionally, the indiscriminate use of antibiotics and antimicrobial drugs in fish farming has led to the emergence of antibiotic-resistant bacteria. This poses a public health risk, as resistant bacteria can transfer to humans. For instance, tetracycline has been shown to induce drug-resistant plasmids in bacteria, making it a regulated substance in many countries (Shepherd and Bromage, 1992).
Treatment and Control Strategies for Causal Agents
1. Bacterial Causes: Avoid overcrowding and over-fertilizing the pond to prevent algal blooms and oxygen depletion. Practice recommended feeding rates.
2. Fungal Causes: Maintain good pond sanitation, regular feeding, proper stocking, and fertilization to prevent fungal infections.
3. Viral Causes: Similar to bacterial and fungal prevention, practice proper sanitation and management to prevent viral outbreaks.
4. Parasitic Causes: Keep ponds free of weeds and control predators. Apply lime at recommended rates for disinfection.
Management-Related Causes
Management-related hazards are often due to mismanagement of resources such as water quality, feeding, and overcrowding. Seeking technical assistance from extension workers and adhering to proper pond management practices can help mitigate these risks.
In conclusion, fish farming presents several hazards to farmers, attendants, and consumers. However, these risks are not exclusive to aquaculture. This review aims to raise awareness about the potential occupational hazards involved in fish farming, encouraging farmers to adopt preventive measures to protect both themselves and their produce.
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