Underwater and largely out of sight, it’s long been assumed that catfish spend winter months on pond bottoms, lethargic and uninterested in feeding. A two-year study conducted at the University of Arkansas, Pine Bluff, is challenging that notion.
As director and researcher at the Aquaculture/Fisheries Center at the university, Carole Engle does much work with the economics of catfish production. Engle is interested in winter feeding because, besides being a function of biology, it also impacts producers’ bottom lines. Engle and colleagues are trying to determine how essential the feeding is.
It takes two years from the time a producer stocks a fingerling until he harvests a catfish. Because of that, “we build economic models over a two-year period,” says Engle. “Most farmers stop feeding in October and pick back up in April. There’s a five-month period that we don’t know much about. Are the fish losing weight or not? If so, how much? Does the size of the fish play a part?”
In the researchers’ models, any answer plugged into the above questions “changes the results of our analysis. So we went back and did a very simple study to get some basic numbers. There have been winter-feeding studies before, but they’ve been complicated, making it hard to sort out basic production values from them. For example: what’s the survival rate of large fish over the winter? We need those numbers for our economic models.”
Because winters are so variable, “we looked at this over two winters. In the study, five ponds were fed and five weren’t. We fed according to the standard recommendations for winter feeding that Extension folks have been citing for many, many years.
“What we found was unexpected: even the fish that were fed over the winter lost weight. The recommendations for winter feeding kept them from losing as much weight as the unfed ponds. But it was bothersome that even the fed fish lost weight.”
Engle decided to take a closer look. It’s no good when producers put all that money and feed into them during the first growing season only to see weight — and profits — shed over the winter.
So, last winter, “we tried to figure out if we weren’t feeding enough by following the standard recommendations or if we weren’t feeding often enough.”
Catfish were placed in concrete vats and fed full-sinking pellets. The pellets were placed on a feed tray “that looks like a square, fine-mesh net that was placed on the tank bottoms. Every day, we’d pull the trays out and count the pellets to see exactly how much the fish had eaten.”
Water was pumped in from the bottom of a pond to keep temperatures in the vats close to what would be experienced in the pond. Data-loggers that continuously measured the temperatures were also employed.
After the winter study and data-crunching, “what we found was rather surprising — except to our facility manager. He’s been telling us this for a long time. He’s out feeding fish constantly, so he’s knows what’s going on. The study proved him right.”
For a long time, the manager has been saying catfish will eat at far colder temperatures than is commonly thought. The study showed catfish continue to eat daily down to water temps of 45 degrees. Lower than 45 degrees and they quit eating — “there’s no point feeding at that level.”
The standard winter recommendations say that at temps below 55 degrees, producers should only feed once per week. That’s not enough, says Engle.
“At 55 to 70 degrees, the standard recommendation is to feed every other day. We don’t think that’s enough — the fish might need to be fed five days a week, or so.
“At different temperatures, the amount they consumed was close to what the recommendations called for. So, on the days they feed, the recommendations called for the right amount of feed.”
The difference came with the number of days catfish need to be fed.
“A lot of people think — and I did too — that catfish just go to the bottom and sit there all winter. But now, I’m convinced they’re looking to eat more often than we expected.”
The fish didn’t lose weight when fed every day. Even so, Engle doesn’t know if daily feeding will become the recommendation for winter feeding. “We’re going to run some other studies this winter to pin that down and take a close look at the costs of feeding more often as compared to the benefits of feeding more often.”
The other important implication of the study involves the disease called visceral toxicosis of catfish (VTC), “a rather tough disease to work through. Catfish can acquire it by eating dead fish in the pond.”
The disease tends to pop up from time to time and usually shows up when there is higher mortality over the winter. There’s not yet a medication that can help control it.
“Well, if the catfish are looking to eat more than we’ve realized, they may be moving to the dead fish because feed isn’t available. By offering more feed, more often, that might cut down on losses from VTC.”