Winter Kill fungus high in recreational catfish ponds, absent in commercial fisheries
By Ryan McGeeney
U of A System Division of Agriculture
April 17, 2019
• Saprolegnia detected in at least 35 catfish specimens from ponds around state
• Not seen in commercial fisheries
• Incidence tied to rapid temperature changes
LITTLE ROCK — Although Cooperative Extension Service researchers said Arkansas experienced higher-than-average rates of the fungus known as Winter Kill in catfish in recreational and farm ponds throughout Arkansas this winter, the fungus is not expected to affect commercial production of the fish.
Anita Kelly, extension fish health specialist for the University of Arkansas Pine Bluff in Lonoke, said her laboratory detected the Saprolegnia fungus in about 35 fish that were sent in over the past winter — roughly a 400 percent increase over typical detection rates.
“In the past, our Winter Kill due to Saprolegnia in ponds averages about seven cases per year,” Kelly said. She said the 35 identified cases did not include diagnostic guesses based on telephone calls from pond owners.
A likely contributing factor to the high rate of Winter Kill this past winter was a series of extreme temperature changes occurring over a relatively short period of time, Kelly said.
“We had some cold days in the winter, then it warmed up to 70 degrees, then it dropped down to 40 and the 30s, and so on,” she said. “I’ve seen more cases this year than I have in previous years.”
Kelly said her lab hadn’t identified Saprolegnia in samples from any commercial catfish operation in the state.
Kelly said the fungus typically weakens the immune system in catfish, causing them to succumb to other natural forces. Fish infected with the fungus typically exhibit letheargic behavior, she said, and by the time symptoms present themselves, mortality is likely to follow.
“There’s not a lot [pond owners] can do about it if they discover it early,” Kelly said. “You’re going to have some mortality related to it. The majority of people don’t notice until they see a dead fish, because most fish stay down in the water column, they don’t often come up to the surface. But if you see them, they’ll be pretty slow and lackadaisical.
“Somebody working with an aquaculture production pond would notice, ‘there’s a few dying today, and there’s a few more the next day,’” Kelly said, “because they go out and check things more regularly than a traditional farm pond owner would do.”
Carole Engle, Extension Director and Chair of Aquaculture and Fisheries, University of Arkansas at Pine Bluff, said Winter Kill hasn’t been common in commercial catfish operations in recent years because the fisheries are typically closed systems that don’t rely on open streams or ponds, thus limiting the opportunity for a fungus to enter the system.
Some Arkansas commercial catfish producers have switched to raising a hybrid catfish over the last six or seven years, Engle said, which has also helped growers avoid Winter Kill. The hybrid was developed from a combination of Blue and Channel catfish, both of which are native to Arkansas. The fish mature to a larger size relatively quickly, Engle said, reducing their vulnerability to the fungus.
Additionally, most commercial operators aim to sell most of their stock by September of each year, thus avoiding maintaining fish counts through the colder months when the fungus typically affects catfish.
“There were years in the past when we saw a lot of winter kill on commercial catfish farms when farms couldn’t sell the fish in the fall, so they had to go into the winter with a lot of fish.,” Engle said. “Usually, that happens when there’s an oversupply of fish. Not everybody can get their fish sold in the fall, and they’re forced to carry a large portion of their crop over the winter.
“Right now, the last season or two, we’re in a situation of very short supply of farm-raised catfish, which means that most growers, when they get fish up to market size, they’re not having a lot of trouble selling them,” Engle said. “Most farms prefer to sell them, rather than incur the risk of trying to hold them over the winter. Prices are pretty good right now.”
According to a January report from the U.S. Division of Agriculture, Arkansas has approximately 5,800 water surface acres dedicated to commercial catfish production, a decrease of about 1,000 acres from the previous year. Arkansas ranks third in acreage, behind Mississippi, with about 41,000 water surface acres, and Alabama, which has about 15,300 water surface acres. Arkansas commercial catfish operators generated approximately $21.3 million in total sales in 2014, according to the report, accounting for about 6 percent of total catfish sales nationwide.
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