Monday 19 November 2018

Epigenetics: The Case for Wild Enhanced Salmon


DNA in wild and hatchery fish from the same river may be the same, but expression of genes may differ widely. They result in different outcomes, that begin and end in different periods of a salmon’s life. Measuring effects in the ocean is difficult because it is difficult to find the fish. But epigenetic effects can be studied during raising fry, and in mature fish when they return.

There is indeed proof that, as odd as it may sound, a wild/enhanced salmon may be a better fish. Epigenetics is the physical and molecular processes that control how DNA gets expressed day to day in structural and functional proteins. How a fish is raised, changes how a gene is expressed. Stress, chemicals, feed and maturation cause epigenetic changes. Some are temporary, others last forever.

Louis Bernatchez, working at Laval University, has found that feeding and crowding in hatcheries accounts for much of the differences in gene expression. Perhaps surprisingly, this effect is consistent for fish of different stocks raised at different hatcheries. But, if you were brought up to gorge on brown pellets that nice people, or machines tossed at you, rather than be hungry all the time, have to hunt to find something to eat and stay out of the way of predators, the expression of some genes could dramatically differ. 

You will recall that evolution functions through ‘natural selection’ a concept that is the basis of all Darwinian thought. Do hatcheries ‘select’ gorgers, or is the food, temperature, relatively inactive life modifying gene expression? Regardless of the explanation, hatchery fish don’t always respond as well as wild fish. 

It is common, at least for chinook, for the fish to lose some or all of their ability to spawn in the wild. This may be good for wild genetics, but it suggests an important reason to rely more on habitat restoration than enhancement, something made all the more difficult in this time of climate warming, with its accompanying lower water flows, higher temperatures and lower oxygen in rivers. 

The Nitinat Hatchery has been doing some interesting experiments in the past few years to try and find the answers. Researchers Kristi Miller and Sean Rogers are working with them. Miller you will know from the Cohen Commission presentation of her ‘Viral Signature’ work that showed sockeye dying at advanced rates of pre-spawn mortality in the Fraser. And she showed in 2017 that PRV causes HSMI, a serious problem for wild fish as up to 95% of farmed fish have PRV. So we need those enhanced fish to return and spawn.

On the other hand, you may have had a serious laugh at the Jimmies, as one-year returnee hatchery male chinook salmon have been dubbed in the Sarita and Nitinat rivers. Plop a generic Tom Thumb dry where they are snapping away and you can ding every one in the pool. They look like pink salmon, but have long, black, sharp teeth, and that unmistakeable smell of a chinook. These, along with Jacks, sexually mature two-year-old males, that no one really wants - except in very low water - are the result of epigenetic changes in hatchery chinook.

The Nitinat has, with both coho and chinook, found interesting things by varying food, lifestyle, size of smolt at release and so on. They do both small and large chinook smolts and yearlings. They also compare standard raceway fry with others that have an ‘enriched’ lifestyle, such as putting objects, bushes, flotsam in their water to explore, hide in, feed on those mayflies, stoneflies and caddis flies that show up on high algae objects, rather than solely pellets.

They also put fry into local lakes to bring themselves up, particularly coho. The aim is to produce fish with more wild behaviour, fish that have a greater chance of wild spawning, and reduced percentage of young, sexually-mature males. The more the epigenetics are right, the better the fish; thus enhancement can become a better option for increasing salmon spawner numbers of wilder fish; in other words, a true companion to the over arching need for freshwater habitat restoration, the crux of the other half of the story.

Some Nitinat experiments of smaller, fitter fish lead to larger adults, and for chinook, the larger fish are typically female, the sex we want to return, not to mention that more five-year fish are returning as, yes, larger fish. Current experiments suggest that environment enrichment doubles smolt to adult survival, an important consideration when wild return is about 1% to maintain a run. So, we may be heading to lower density, lower growth rates and enriching environment more consistently across the Salmon Enhancement Program. 

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