What to Do When Fish Get Sick: Identifying and Treating Common Diseases in Farmed Fish

What to do when fish get sick is a problem that both aquaculture farmers and ornamental fish hobbyists encounter. Fish live in water, and the early stages of disease are often hard to notice; by the time obvious symptoms appear, the condition may already have spread. Therefore, learning to identify and correctly handle it early is the key to reducing losses.

Fish diseases can broadly be divided into parasitic, bacterial, and fungal diseases, as well as environmental diseases caused by deteriorating water quality or nutritional deficiencies. Common abnormal signs include gasping at the surface or sinking to the bottom, sluggish swimming, white spots or ulcers on the body surface, swollen and reddened gills, and reduced appetite. After noticing abnormalities, you should first check the water quality and recent weather changes to make a preliminary judgment as to whether it is environmental stress or a pathogen infection.

In terms of treatment, the first step is usually to improve the aquatic environment, such as changing some of the water, increasing aeration, and reducing feeding; many mild symptoms will ease as water quality improves. If a pathogenic disease is suspected, the sick fish should be isolated for observation promptly, and then, according to the symptoms, deworming, antibacterial, or disinfectant medications should be chosen. When using medication, the dosage must be strictly controlled, and for food fish, the withdrawal period regulations must be observed to ensure food safety.

Prevention is better than cure. In daily practice, keep ponds or fish tanks clean, regularly disinfect aquaculture tools, and isolate and quarantine new fish before stocking; at the same time, avoid overcrowding and overfeeding. If the condition is complex or continues to worsen, you can ask the local aquatic technology extension department or fish disease prevention and control agency for help with diagnosis, and do not blindly increase the dosage, so as to avoid causing greater losses.