Genetic research streamlines single-sex breeding programs

A research project by Canada’s Natural Sciences, Engineering and Research Council and the University of New Brunswick (UNB) has identified a genetic marker for producing single-sex populations of salmonids. This marker could have a significant impact on salmonid aquaculture.

“From an aquaculture perspective, females are generally more desirable animals,” says the project lead, UNB’s Dr. Tillmann Benfey. “The way we make all-female populations is that we have to look at the genetics behind what determines sex for a species.”

The sex of a salmonid is determined the same way as in mammals – eggs always have an X chromosome while sperm carries either an X or Y. As such, it is the sperm that determines sex and that is the key.

“Knowing that, if we want to make an all-female population, we take fish that are genetic females and we use hormones to sex reverse them so they become functional males,” says Benfey. “They produce sperm, but because genetically they’re females, the sperm that they carry always gives us female progeny.”

However, it can be extremely difficult to determine natural males from females who have been turned to functional males.

Benfey says that determining the difference was extremely tedious by conventional means. When faced with a tank full of fish and unsure which were genetically altered, they had to test every male fish to determine their family. It was only when the fish began to spawn a year or two later when they could truly see whether the offspring was a mix of males and females or an all-female population.

“Our goal was to take a blood sample and look at the DNA and be able to say [whether it was male or genetically female],” says Benfey.

Benfey turned to the Prince Edward Island-based Center for Aquaculture Technologies Canada (CATC), which using the genetic marker, was able to correctly determine natural males from females who were functional males with a 100% success rate.

“It was a proof of concept that this tool, originally for rainbow trout, would work with other species,” says Benfey. “This one marker works for several different types of salmonids. It’s now a question of ‘will breeding programs adopt this technology?’ And that’s really beyond the realms of the experimental work that we’re doing here. It’s the type of approach that I’d like to apply to non-salmonid species but there aren’t any candidate species from an aquaculture perspective right now.”

— Matt Jones