Crossed humpback salmon and Atlantic salmon

Researchers at the Institute of Marine Research have for the first time produced viable hybrids between humpback salmon (Oncorhynchus gorbuscha) and Atlantic salmon. The goal is to determine whether such crosses can survive to adulthood and what risks this may pose.

"We wanted to find out whether different crosses with humpback salmon can produce viable offspring that survive to adulthood, and whether this could pose a risk to Norwegian salmonids," says marine scientist Monica Solberg in an article on the Institute of Marine Research website.

Only one type of cross survived

The experiment was conducted a little over two years ago, where researchers tried to cross humpback salmon, also known as pink salmon, with various species of salmonids – including Atlantic salmon, char, trout and rainbow trout. Humpbacks are a Pacific species but have been periodically introduced into rivers of the White Sea and Barents Sea basins in Russia for decades, and strays have been found in many Norwegian rivers and sometimes in the UK. 

"Of all the salmonids we tried to cross with humpback salmon back in 2023, only one cross resulted in survival," says Solberg.

The only combination that produced viable offspring was when an Atlantic salmon was the mother and a humpback salmon was the father.

"In all the other crosses, the humpback salmon was the mother. Then we didn't get any survival at all."

She explains that eggs from farmed salmon were fertilised with sperm from humpback salmon. The result was fish that were genetically half of each species.

"We took eggs from farmed Atlantic salmon and fertilised them with sperm from humpback salmon. These fish are a 50/50 mix of the two species. We knew this was possible, but we got a much higher survival rate than expected."

Now the researchers plan to test whether more crosses with humpback salmon fathers can be successful with other local salmonid species.

Looks like mum - but grows like dad

The analyses show that the hybrids have traits from both parent species.

"Humpback salmon have a black tongue, which is a clear characteristic of the species, while some hybrids have a completely white tongue. Some also lack the spots on the tail fin that are typical of humpback salmon, and thus resemble more like regular Atlantic salmon," explains Solberg.

The researchers also see large differences in growth.

"Humpback salmon grow faster than (Atlantic) salmon, so that growth is definitely something the hybrids have from their humpback salmon father."

Low risk in nature

Although crossbreeding can be done under controlled conditions, the risk of such hybrids occurring in nature is considered low.

"Wild salmon usually spawn from September to November, while humpback salmon spawn earlier, often in August-September."

The marine scientist nevertheless points out that the spawning period can vary.

"In Northwest Russia, it has been observed that humpback salmon can spawn as late as October, which may overlap with the spawning of Atlantic salmon."

In Northern Norway, there may also be overlap in spawning with species such as char and trout.

"Therefore, it is important to gain even more knowledge about whether there is actually a possibility of crossbreeding with all our local salmonids," she adds.

Will continue to follow the hybrids

The researchers expect that the humpback hybrids cannot reproduce. 

Crossbreeding between wild salmon and trout is relatively common, but they are more closely related to each other than they are to humpback salmon. 

"Usually, hybrids between salmon and trout are sterile, and we therefore expect that our hybrids between salmon and humpback salmon will also be sterile," says Solberg.

“Sexual maturation has not been documented in similar hybrids before. We will monitor how they develop further, until they are adults,” she says.

Read more about the project here.