Hybrid catfish grading solution

While hybrid catfish provide many benefits and much promise for Southern aquaculture, they do present several unique challenges — challenges researchers are determined to find solutions for.

One of the problems is, compared to the channel catfish the aquaculture industry has been built upon, the hybrid has a smaller head in relation to its body size. Because its head is smaller the fish tend to “gill” themselves when being sorted.

“They can get their heads through the net up to the gills then get stuck,” says David Heikes, Arkansas Extension catfish specialist. “Lots of hybrids get hung up in the traditional harvesting nets.”

Many farmers want to raise hybrids because they’re hardier, have improved growth rates and improved feed conversion. Hybrids have “some superior growth characteristics and appear to have better yield characteristics, as well. We’re still learning how to best grow the hybrids — how often they need to be harvested, stocking densities and other things. But many producers like them very much. It appears to be more disease resistant and that’s a plus.”

Hybrids are aggressive-eating and fast-growing and producers must be committed to feeding the fish regularly.

Because they’re so difficult to produce (see http://deltafarmpress.com/news/070117-catfish-hybrid/index.html) hybrid fingerlings cost more than a standard fingerling — there are simply more steps in producing them. In order to pay off, “you must have better feed conversion, growth rates and yields. That can be achieved if you’re willing to feed hybrids all they want to eat. Of course, feed is more expensive right now.”

And then there’s the grading issue.

“If we could find a way to grade them at harvest size, it would be a win-win situation.”

It appears Heikes may have found the answer.

“Over the years, I’ve worked on different grading systems. The floating in-pond grader was essentially a bar-grader with horizontal bars just below the grading surface. It was used on hybrids, but the problem is there are so many fish at harvest to process through that machine.”

Using the bar-grader is labor-intensive and can cause stress on the fish if they’re crowded for too long.

“The bar-grader has a place in the fingerling industry with smaller fish. But, when switched to grading larger hybrid food-sized catfish — which is a strong, physical animal — the in-pond grader is very difficult to use. It just takes too long with too much effort.

“Farmers have been telling me ‘We need a more passive grading system. We need to be able to run fish into a harvest net and somehow allow them to grade.’”

Heikes’ solution is a flexible panel that can be sewn into the side of a harvest net. The panel is made of rigid PVC bars held at various increments with industrial plastic spacers. Those are strung together on a galvanized aircraft cable.

“Essentially, I’ve come up with a 4-foot-tall, 20-foot-long, flexible grid with a set aperture. The aperture is set according to what fish we’re going after. For example, if we want fish to go to a regular processing plant, we’ll choose a spacing around 1.9 inches. For a gut-market plant, we’ll choose a much wider spacing.”

Three of the panels are sewn into an 80-foot harvest sock. That provides 60 feet of effective grading surface. The sock design is standard, although small mesh (1 inch) to prevent any fish from being gilled.

“We just cut the side out and sew in the flexible panels. The only grading that can happen is through the panel. Because it’s a set bar spacing, it provides a cleaner cut than a net.”

Heikes has been working with producers using the new design for about a year. “I’m getting some good feedback and that’s rewarding.”

The reason Heikes started working on the grader was “an immediate need. In order for the hybrid catfish industry to be viable and grow, something like this was needed. I think this will work.”

And the concept could also be used to grade fish other than hybrid catfish. Most other farm-raised species must be graded by hand with box graders or some sort of mechanized grading machine.

“I think this grading approach could also be used for hybrid striped bass among others. I hope to work with other species in the coming year.”

How to acquire the graders?

“They’re for sale through Delta Net and Twine, an operation out of Greenville, Miss. They make the vast majority of all commercial catfish grading nets.”

Hydraulic trawl

Along with researchers in other Southern states, Heikes is working on a hydraulic trawling system that could be used for sampling commercial catfish ponds for inventory purposes.

“Through October, I’ll be working on a farm in south Arkansas looking at this. We’re trying to find the best way to pull the trawl through a pond. Essentially, we’re making use of an otter trawl — a net that has a wide opening at the front and contains ‘otter’ boards made of aluminum.”

As it’s dragged through the water, the boards open the net mouth about 30 feet wide. Some 50 feet of tubular net is attached to the mouth where fish are caught.

“I took a standard seine reel and reworked the hydraulics on it. About 1,500 feet of rope is also employed. So, we can lay the rope all around the pond and crank it up on the hydraulic reel.”

The net then makes a sweep through the pond. In trial runs, “we’ve caught anywhere from 500 to 1,000 pounds of fish in about five minutes of trawling. That provides a decent sample of fish.”

The experiments Heikes and colleagues are now doing include ones to determine if the trawled sample of fish is actually representative of the size structure of fish in the pond.

“In other words, are we catching all fish sizes in the right proportions? If we could get this worked out, it would really help producers. That’s because unlike chickens or cattle or hogs, fish producers can’t really see their inventory. It’s hidden underwater. Sometimes it’s difficult to know when it’s time for harvest.”

True, growers have a fairly decent idea how many pounds of fish are in the pond because of the amount of feed that has gone in. If 50,000 pounds of feed is put into a pond, “we expect around 25,000 pounds of fish to be there. But we don’t always know how many head make up the 25,000 pounds. A quarter-pound average weight on the entire population can mean coming up short of what’s needed.”

This trawling system would be good for “planning purposes and to make the industry more bankable. We need to develop some inventory methods.”

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