Prevention and Control Methods for Bacterial Diseases in Loach Aquaculture

Loach (Misgurnus anguillicaudatus) is a warm-water bottom-dwelling fish with both food and medicinal value, and is one of the main freshwater economic fish species in our country. In recent years, due to export earnings and increased market demand, artificial intensive loach farming has developed rapidly, and various bacterial diseases have consequently emerged. The symptoms, causes and prevention and control methods are summarized below for the reference of breeders. 

I. Red-fin disease 

1. Symptoms  This disease mostly occurs when water quality deteriorates and fish are improperly kept, caused by Brevibacterium infection, and is prevalent in summer. The epidermis on the body surface or fins of diseased fish peels off and turns grayish-white, the anus reddens, and then red patches appear on the abdomen and flanks, gradually turning dark red; the intestines become ulcerated, and subsequently Saprolegnia parasitizes the skin ulcer sites, triggering saprolegniasis. Diseased fish hang suspended at the water inlet of the pond or near the water surface at the pond edge, and do not feed. 

2. Prevention and control methods  Apply 1 gram of bleaching powder solution per cubic meter of water, splashing it over the entire pond. Or dip the fish in a solution containing 10 mg to 15 mg of chloramphenicol, oxytetracycline or chlortetracycline per ml for 10 to 15 minutes, once a day; results can be seen in 1 to 2 days, and full recovery in 4 to 5 days. 

II. Hemorrhagic disease 

1. Symptoms  This disease has appeared in recent years, and the specific bacterium causing the infection remains to be confirmed. It occurs easily from early spring to October. The body surface of diseased loach shows punctate, patchy or diffuse congestion and hemorrhage, with internal organ hemorrhage as well, presenting symptoms of septicemia. 

2. Prevention and control methods  Splash bleaching powder or sodium dichloroisocyanurate over the entire pond, or feed 10 mg to 15 mg of oxytetracycline per kilogram of loach mixed into the feed. 

III. Enteritis disease 

1. Symptoms and causes  It is prevalent when the water temperature is above 20°C, caused by infection with enteric punctate Aeromonas. The intestinal wall of diseased loach becomes congested and inflamed, the abdomen swells, red patches appear, the body color darkens, the anus becomes red and swollen, and the intestine turns purplish-red with yellow mucus. This disease often occurs concurrently with gill rot disease and red-skin disease. 

2. Prevention and control methods  Splash bleaching powder over the entire pond or administer furazolidone orally. 

IV. Gill rot disease 

1. Symptoms and causes  When stocking density is high, water quality is poor, and water temperature is above 15°C, the loach body is infected with Flavobacterium columnare, causing decay of gill tissue. Diseased loach darken in body color, the gill filaments rot and turn white, the cartilage at the tips is exposed, and the gills carry sludge and abundant mucus; in severe cases, they develop an “open skylight” appearance. 

2. Prevention and control methods  Splash bleaching powder for disinfection or administer norfloxacin orally.