Just as cattle producers and other farmers should get ready for winter, so should catfish farmers.
“Catfish should be ‘winterized’ to boost the health of the fish and maintain their body weight during the winter,” says Larry Dorman, University of Arkansas at Pine Bluff Extension fisheries specialist at Lake Village, Ark.
As temperatures drop, the metabolism of the fish slows and fish eat less, sometimes only a couple of times a month. It is imperative that they be in optimal health before going into winter, said Dorman.
Winterizing fish includes establishing a winter feeding program and maintaining good water quality as well as knowing what to do if the pond freezes over.
In the past, farmers stopped feeding fish in late fall and started back again in the spring. “This is not good,” said Dorman. “Fish can lose up to 15 percent of their weight in winter, and feeding as little as two or three times a month, their weight can be maintained.”
A winter feeding program helps prevent diseases related to vitamin deficiencies and helps maintain a high fillet percentage. Processors want fish with a minimum fillet percentage of 44 percent. Unfed fish have a lower fillet percentage.
Dorman recommends initially feeding fish every other day. Feed 1.5 percent to 2 percent of the total weight of fish in the pond. As the water temperature drops, lower the feeding rate to 0.5 percent to 1 percent of body weight, and feed only once or twice a week. Stop feeding when the water temperature drops below 55 degrees.
Check the water quality in ponds weekly during the fall. If ammonia levels are high, check the pond water twice a week. As water temperatures drop below 55 degrees, check twice monthly. Resume checking weekly in the spring and continue until June 1.
“High ammonia rarely kills fish directly, but ammonia can be converted to nitrite,” said Dorman. “If conditions are right, high nitrite levels can cause brown blood disease, which kills catfish.
“The nitrite in the water combines with the hemoglobin in the fish's blood, preventing it from carrying oxygen. The fish become starved for oxygen even though there's plenty in the pond,” noted Dorman.
To prevent nitrite problems, Dorman recommends adding salt, sodium chloride, to the pond. In the fall, add one-half to 1 ton of salt per acre. This will increase the chloride level of the pond to 60 to 100 parts per million.
Catfish farmers should know the total weight of fish in each pond as winter nears. Dorman says that research shows that ponds with 4,000 or more pounds per acre going into winter are apt to suffer from winterkill syndrome. If fish are on flavor, Dorman recommends harvesting the larger fish.
Winterkill is due to a shut down of the immune system of the fish. The skin of the fish loses its slime coating, becomes dry and develops fungus-covered lesions. The fish may die. The fish also exhibit a sunken eye condition. A reoccurrence of these symptoms happens after each cold front.
Dorman said research suggests that periodic applications of copper sulfate will kill the fungus spores in the water. If winterkill occurs in your ponds or the ponds have a history of winterkill, treat them just prior to the passage of a cold front.
Ponds may have to be treated 10 or more times. A water quality test is necessary to determine the amount of copper sulfate to add to the pond. A typical 10-acre pond with an average depth of 4.5 feet may need a total of 1,800 pounds of copper sulfate at a cost of $1,150. At mid-October 2001 prices, 2,021 pounds of fish are needed to pay for that treatment.
“Although ponds freezing over are not a typical problem in south Arkansas, they could be and are a real problem further north,” said Dorman.
Last winter ponds were covered with ice for a week. And, when the ice thawed, several catfish farmers discovered 250 pounds to 1,000 pounds of catfish per acre were killed or were suffering from winter fungus disease.
Snow-covered ice or opaque ice prevents sunlight from penetrating the pond. Reduced sunlight means reduced photosynthesis, thus reduced oxygen levels. Fish can die from a lack of oxygen under ice-covered ponds.
If the ice lasts more than three days, Dorman recommends starting the well and melting a small area of the pond. This lets gasses exchange and may prevent fish losses.
Carol Sanders is a writer and editor for the University of Arkansas at Pine Bluff School of Agriculture, Fisheries and Human Sciences.