This is ascitic scale disease and loose scale disease, and the mortality rate is very high within 48 hours, which must be treated immediately. Treatment plan: Take out the sick fish, soak the fish in 3% sodium bicarbonate solution for 10 minute (the salt is great, but the effect is poor), then use yellow powder to add gentamicin and five thousandths of salt to take a medicine bath for 2 hours (or take a medicine bath for 24 hours according to yellow powder), once a day for several days, and you can be cured. You can also soak the fish in malachite green or methylene blue solution with a concentration of 3 grams per ton of water for 5 minutes, then wash the fish and take a bath with gentamicin and yellow powder.