In a recent study, hybrids were grown in ponds and then measured for growth and meat yield. The analysis indicated the presence of substantial genetic effects of parents on offspring performance.

“This shows we can improve hybrid catfish growth and carcass yield by selecting superior female channel catfish and male blue catfish as parents,” Bosworth says.

Waldbieser also designed a rapid DNA-based test that identifies and distinguishes channel, blue, and hybrid catfish within 24 hours at all life stages, from 1 day after fertilization to a cooked fillet.

“The test is a useful tool for hybrid production management and postharvest detection of hybrid catfish products,” he says.

In other research, physiologist Brian Peterson investigated the relationship between catfish growth, immune function, and genes during early stages of development. Egg samples were taken before and after fertilization, and embryos were collected at hatch and at “swim-up”—the stage when fry are not yet sexually developed.

Peterson examined changes in gene expression of insulin-like growth factors (IGFs) and toll-like receptors (TLRs), molecules involved in the induction of the immune response, in hybrid and channel catfish. Over time, gene expression levels of TLR5 and IGF-I mRNA increased in channel catfish. In hybrids, TLR3, IGF-I, and IGF-II mRNA increased.

“It was known in mammalian species that IGF-II played a primary role in fetal development. The biggest surprise in our catfish studies was that IGF-II plays a role in both fetal development and juvenile growth,” Peterson says. “IGF-I in catfish also plays a role during fetal development and growth.”

Making the grade against disease

Proliferative gill disease (PGD) is one of the most devastating parasitic infections affecting catfish. The deadly disease damages the gills of fish and decreases their ability to get oxygen from water.

To find out if hybrids are more or less susceptible to PGD, Bosworth and his colleagues looked at gill damage in different lines of channel, hybrid, and blue catfish. Juvenile catfish were placed in a commercial pond where catfish deaths were attributed to PGD. They then identified and examined channel catfish and hybrid families with the most gill damage and those with the least gill damage.