What is in this article?:
• For decades, it’s been known that hybrid catfish — a cross of the fast-growing channel catfish with its close relative, the slower growing and larger blue catfish — generally have better growth, higher survival, and better meat yield than either channel or blue catfish.
• But hybrids have been difficult to produce in large quantities.
• That’s changing.
Look at water quality
One approach is to look at the effects of water quality, such as its calcium content, or “hardness,” on the hatching success of eggs. Working with fish biologist Les Torrans, Chatakondi incubated fertilized hybrid eggs in waters containing four levels of calcium hardness to determine which level yields the highest hatching success. The calcium hardness levels ranged from 25 milligrams per liter to 100 milligrams per liter — levels maintained by commercial hybrid hatcheries. They found that lower calcium levels may reduce hatchability and increase vulnerability to diseases.
“We recommend a calcium hardness level of 75 milligrams per liter in waters to hatch hybrid catfish eggs,” he says.
“Optimal levels improve the egg-hatching success and may contribute to a lower cost of producing hybrid fingerlings.”
Additionally, not all eggs are created equal. Hormone-induced fish often ovulate eggs that vary in quality due to variation in brood fish maturity, husbandry, nutrition, genetics, and mechanical damage during manual spawning. Poor-quality eggs are more vulnerable to fungi, which could spread to healthy eggs.
Chatakondi developed a method, which can be easily adopted in catfish hatcheries, to identify poor-quality eggs before they hatch. He found that the pH level of ovarian fluid of stripped channel catfish eggs prior to fertilization can be used to predict hatching success in hybrid embryos.
It appears that a pH level of more than 7.0 is indicative of better quality eggs, and using egg lots of this pH or higher can improve hatching rate, Chatakondi says.
Genetic tools for breeding
Scientists are constructing a genetic map of the catfish genome to identify chromosomal regions that control significant traits — such as meat yield and disease resistance — that are essential for selective breeding programs.
Molecular biologist Geoff Waldbieser has developed DNA markers to analyze channel catfish parentage and kinship to determine genetic diversity, produce pedigree populations, and identify markers associated with important traits. This technology is being used to learn more about genetic background to further improve hybrid performance.