“The hybrids are unusual,” says Dr. Rex Dunham, “But it’s probably the best example of genetic improvement in aquaculture ever.”
Dunham is the lead of a project started in 2009 at Auburn University in Alabama to produce a hybrid of channel catfish (Ictalurus punctatus) and blue catfish (Ictalurus fucatus) with an ideal combination of traits. The list of traits being combined is stunning.
“They have improved growth rate, they have improved feed conversion efficiency, they’re more resistant to several diseases, they tolerate lower oxygen than the parents, they’re easier to harvest than channel catfish and they’re also good for the processor because they have a better fillet percentage than the parents,” says Dunham.
One of the key aspects of Dunham’s research is choosing the right parental strains to combine – different strains have different combining abilities, and choosing the right strain to cross will have an impact on the performance of the hybrid.
“Essentially, it’s selecting individuals within the parent species that produce better than average hybrids,” says Dunham. “When we’re looking at different strains or looking at trying to identify individuals with combining ability, what we’re doing is taking a holistic approach where we’re trying to improve all these traits.”
Another important consideration is at the hatchery level, as there is a large difference between the different strains regarding how easily they will produce hybrid embryos through the artificial fertilization technique used. The end goal is to match the greatest hatchery output with the enhanced growth and disease resistance traits; however, the output can vary as much as three-fold depending on which parental strains are used.
“We’re to the point where we have enough reproductive problems solved that the next step is to focus more on different ways to genetically enhance the hybrid,” says Dunham.
The process is time consuming, however. The generational interval for channel catfish is between three and four years and between four and five years for blue catfish. As such, when trying to find individuals who would produce a better performing hybrid, it can require up to five years of waiting to see what the response is, and it may take several generations to make significant progress. This is both a positive and a negative, Dunham notes.
“There’s so much to do, if a generation interval were any shorter, I don’t think I could handle the workload,” laughs Dunham. “With the experiments we’re doing now, we’re obtaining estimates of how successful that approach should be, so it will be another two to three years before these fish are old enough that we can actually test the predictions to see if that approach does increase the hybrid performance or not.”
While the current experiments are in progress, the Auburn University effort has already made an impact on the industry – Dunham partnered with Alabama’s Eagle Aquaculture to introduce the protocol they developed to produce the hybrid embryos to the commercial industry. Due to these efforts, Dunham says, the technology has been widely adopted in the US aquaculture industry.
“About 50 per cent of the industry is now a hybrid catfish industry,” notes Dunham. “We project that will continue year after year until it reaches near 100 per cent adoption. In regards to this continued genetic improvement, building a better and better hybrid, the reproductive technology is in place in the industry for ready adoption.”
While Dunham continues to collaborate with Eagle Aquaculture and other partners, such as the USDA’s genetic research unit in Stoneville, Mississippi, they are still seeking further industry partners.
— Matt Jones
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Caption: “About 50 per cent of the industry is now a hybrid catfish industry.” Dr. Rex Dunham, Auburn University. Photo courtesy of Rex Dunham.
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Caption: Auburn University project started in 2009 to produce a hybrid of channel catfish and blue catfish with an ideal combination of traits for the aquaculture industry. Photo courtesy of Rex Dunham.
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Caption: Male blue catfish selected for breeding. One of the key aspects of Dunham’s research is choosing the right parental strains to combine to improve the performance of the hybrid. Photo courtesy of Rex Dunham.
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Caption: Loading out hybrid catfish after grading. Photo courtesy of Rex Dunham.