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The key link of pollution-free fish farming
In addition to using pollution-free fish and feed, the key factor in preventing and controlling fish diseases lies in maintaining a healthy aquatic environment. Below are some effective practices that have been proven to reduce disease occurrences in fish farming.
Studies on symbiotic environments have shown that when aquatic plants coexist with fish in the same pond, fish rarely suffer from diseases. This discovery has opened new possibilities for disease prevention in pollution-free aquaculture. In fish ponds, common aquatic plants include rice and lotus roots. These should be planted in an east-west direction, with spacing of about 33 cm, covering no more than 50% of the pond's surface area to ensure good light penetration. The water depth should match the needs of the plants—typically up to 30 cm for rice and over 50 cm for lotus roots. Fish waste and leftover feed settle at the bottom and decompose, which can pollute the water and promote harmful pathogens. However, aquatic plants absorb these as nutrients, reducing the breeding grounds for diseases and keeping fish healthier.
Newly cultivated fish ponds that combine planting and farming tend to have fewer pathogens, resulting in lower disease rates. In contrast, older ponds often face more disease issues. To manage this, it’s advisable to rotate between fish farming and plant cultivation. For example, one pond can be used for fish in one year, while another is planted with crops. The next year, they are swapped. Since pathogens that affect fish do not harm plants and vice versa, this rotation helps reduce disease occurrence in both systems.
Herbal remedies can also play a role in disease prevention. Plants like pine needles, eucalyptus leaves, willow leaves, buckwheat leaves, and water calamus are commonly found near fish ponds. When dead fish appear or fish stop feeding suddenly, these herbs can be collected, chopped, and boiled in clean water. After the water turns brown (which is safe for fish), it can be applied at a rate of 15–30 kg per mu. This natural remedy helps control potential diseases and prevents their spread.
Ecological diversity enhances the resilience of fish pond ecosystems. The more species present, the stronger the system becomes in resisting diseases. If only one or two species dominate, especially if they make up over 50% of the population, they are more prone to illness. By introducing multiple species such as grass carp, bigmouth bass, black mullet, Chinese sturgeon, turtles, squid, wild fish, snails, and oysters, a complex food web is formed. Predatory fish help remove sick individuals, breaking the pathogen chain, while bottom-dwelling creatures like eels and squids help clean the pond floor, further reducing disease risks.
Observations show that ponds with more fleas tend to have fewer fish diseases. It is believed that earthworms may help suppress pathogens. By placing earthworms in fish ponds, either directly or in baskets, and rotating them every few years, disease incidence can be naturally reduced. This method supports long-term, sustainable fish farming without chemical reliance.
Regarding drug residues, these refer to the remnants of drugs and their metabolites in edible parts of aquatic products. According to the standard "Limits for Fish Residues in Pollution-Free Foods and Aquatic Products (NY5070-2002)," certain antibiotics and chemicals must not be detected in fish. For example, chloramphenicol, furazolidone, and sulfonamides are strictly prohibited. Some substances, like synergists, are allowed up to 100 μg/kg. It is equally important to observe withdrawal periods—the time between the last dose of medication and when the fish can be safely sold. Withdrawal times vary depending on the drug: bleaching powder requires at least 5 days, oxytetracycline 30 days for some species, and oxolinic acid up to 37 days for certain fish. Proper adherence to these guidelines ensures safer, higher-quality fish production.