“This is the first time we have worked with hypoxia as a trait to study,” says Yvonne Sheehan, Brood Program Manager at Marine Harvest Canada. “We hope the researchers will be able to identify a marker on the DNA that is linked to low oxygen tolerances. If so, then we will incorporate that into our breeding program.”
“Low oxygen events are becoming more common on our BC coast,” Sheehan adds. “In conjunction with increasing sea temperatures they result in lower levels of dissolved oxygen.”
UBC researcher Dr. Patricia Schulte says that upwelling of deeper low oxygen water is the culprit. “The data suggests that coastal hypoxia in the regions where net pen aquaculture would be occurring is increasing by about 5% a year,” says Schulte. “And it has been going up exponentially.”
“Prior to about 1996-97 there had been no recorded examples of extreme hypoxia,” Schulte explains. “But over the years these hypoxic events have been increasing both in magnitude and in frequency so they happen more often and they are worse. In 2002 there was a massive die-off of wild fishes and invertebrates in Oregon.”
Sheehan says hypoxia is responsible for “significant losses” at Marine Harvest Canada. “We will find it in different pockets in different areas.” she says.
That’s part of the problem Schulte points out. “Aquaculture sites are often in narrow bays that don’t have a huge amount of flushing so when low oxygen water comes in it stays for a while.”
“Up-wellings can occur quite rapidly without much warning,” says Schulte. “We are not particularly good at predicting when these things are going to happen, although we know they are more frequent towards the end of the summer.”
“We are not at the stage where we are able to say oh this site is going to have a problem we had better move the fish,” she adds. “So it would be really helpful to improve the tolerance of the fish.”
Loss of energy
When oxygen levels drop in the water and fish can’t get enough, they will breath deeper and faster “That’s a problem because it costs energy,” says Schulte. “The fish has a limited amount of energy and what are they going to use that energy for? Maybe it is going to reduce the amount of energy it puts into growth and grow more slowly. Or it might reduce the amount of energy it puts into its immune system and be more susceptible to disease.”
It is standard practice to reduce feed during low oxygen events so as not add the extra stress of digestion to the fish, Schulte explains. It also helps keep uneaten feed from adding to the nutrient load in the water causing more oxygen to dissolve.
“This is the first use of genomic tools for Marine Harvest Canada,” says Sheehan. “We have been using and will continue to use selective breeding programs,” she adds.
It’s a simple procedure Schulte says. They will take random fish from MH’s breeding population, put them in a tank and slowly lower the oxygen. “Until they can’t swim very well, then we will pull them out and take a DNA sample and we will have a range of individuals with different oxygen tolerances.”
“We will be doing some genetic analysis to see how genetically different these fish are,” says Schulte. “Our hope is that we will be able to identify genetic markers that all the good fish share, and all the bad fish don’t have, so then we will be able to identify fish that are likely to be good at tolerating hypoxia just from their DNA sequence alone.”
That work will be done in the lab, at fresh water hatchery sites and eventually in tanks next to saltwater pen sites.
Finding the markers
The Atlantic salmon has a large genetic map Sheehan points out. They are hoping that a low oxygen marker or group of markers can be identified. “But it will be time consuming and laborious for the researchers,” she says.
“What makes me cautiously optimistic is that we have done some work previously that shows us that different families of salmon have different levels of hypoxia tolerance,” says Schulte. “So that suggests that there is a good genetic basis and makes it more likely that we will find a gene.”
“Even if we don’t however, we should be able to deliver information to Marine Harvest about which families in their program are the best,” she adds.
And that is what makes this university-based research interesting says Schulte. “Genome BC has provided us this wonderful opportunity to work together with the aquaculture industry. The project is both at the cutting edge of science and will be potentially very useful for industry especially here in BC because we have this problem with hypoxia.”
— Tom Walker