LSU AgCenter researcher provides tips to reduce disease outbreaks in fish

(05/29/24) BATON ROUGE, La. — Springtime disease losses in fishponds are common throughout the Southeast, especially in Louisiana, according to LSU AgCenter aquaculture specialist Greg Lutz. Many problems that become apparent in the spring begin in the fall, when hot weather can reduce oxygen levels in ponds and make fish susceptible to diseases.

According to Lutz, overcrowding, overfeeding or overfertilizing almost always contributes to these problems and the excessive heat and lack of rainfall experienced across much of Louisiana and the surrounding region last fall exacerbated these impacts.

“After a stressful fall, low temperatures during the winter force fish into a state of slow motion in which they eat very little, and their immune systems respond slowly,” Lutz said. “When temperatures begin to rise in the spring, disease-causing organisms that are naturally present in a pond can get the upper hand on fish that are in a weakened state.”

Lutz went on to say that stress caused by abrupt temperature fluctuations, such as many parts of the state experienced in the past several months, aggravates fish health problems by further suppressing immune responses.

“Bacteria capable of attacking fish are naturally present in almost any pond, and once environmental stressors weaken the fish’s resistance, bacterial infections can often be seen in the form of sores, bruises and discoloration on the skin and fins,” he said. “Bream, bass and catfish can all be affected, with fish losses gradually increasing over the course of several days or weeks.”

Response options are limited when disease outbreaks begin. Pond owners should try to minimize all forms of stress on the fish.

Nutritional stress can be addressed by offering feed, but only what the fish will consume in 3 to 5 minutes each day. Uneaten feed will cause water quality problems, so do not offer feed if the fish are not eating.

Oxygen stress can be minimized through aeration, if aerators or fountains are already in place.

Physiological stress can be reduced by adding rock salt to improve ionic balance in the fishes’ bloodstream. Applying salt at 200 lbs. per acre of pond surface, spread along the pond banks in shallow water, will sometimes help reduce mortalities from bacterial outbreaks.

“There is no guaranteed approach that will eliminate springtime fish losses to disease, but avoiding overcrowding and high levels of fertility throughout the year will help minimize the chances of a fish kill in the spring,” Lutz said.

For tips on all aspects of pond management, check out the LSU AgCenter’s list of topics at

5/29/2024 4:26:27 PM
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