Cultivate and select healthy fry; ? Parents used for breeding must come from the original seed farm and the quality meets the relevant standards. Production conditions and facilities should meet the requirements of production technical operation procedures, and the quality of seedlings must be inspected and quarantined by qualified professional and technical personnel. Control the appropriate breeding density; Reasonable stocking density is an important content of pollution-free aquaculture. Overloaded farming can easily lead to the deterioration of farming environment, the outbreak and spread of diseases, the decline of aquatic products quality and the low commodity rate. The breeding density must be strictly controlled to ensure a good breeding environment. Provide high-quality bait; Bait nutrition is the material basis of pollution-free aquaculture, and reasonable selection of bait varieties and scientific feeding are the key links of pollution-free aquaculture. Advocate the use of compound feed. When using fresh miscellaneous fish, feed them in time to ensure freshness; When using frozen miscellaneous fish, the thawing time should be strictly controlled to avoid spoilage due to sun exposure. Rational use of fishery medicine? ; Disease prevention and rational use of fishery drugs are important parts of pollution-free aquaculture. Medication should achieve "three effects" (high efficiency, quick-acting and long-lasting) and "three small" (small toxicity, small side effects and small dosage). Accurately calculate the dosage and reasonably cast it. On the basis of fully understanding common diseases and their epidemic situation, it is necessary to use fishery drugs rationally to prevent drug residues from damaging the ecological environment of water areas.