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.
See this article for a non-technical take on
epigenetics: https://www.hakaimagazine.com/news/hatchery-fish-often-fail-in-the-wild-now-we-might-know-why/.
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