A few years (OK a few decades) ago, I worked out the concept and kinetics for a chemical reaction that prevented the hemolysis of dialysis patients’ blood. It turns out that the process was also perfect for fishery authorities in the Northwest; allowing them to preserve the health and safety of salmon as they make their mad dash to the sea. (The rivers were “accepting” treated wastewater that was replete with chlorine; using ascorbic acid is a quick and effective way of tying up the free chlorine that hemolyzed blood and harmed salmon)

That’s why I’ve kept the salmon (and other fish) breeding efforts on my radar.  To see how well my little idea is working, keeping those hatchery-bred salmon healthy.  (After all, who doesn’t love a wonderful salmon dinner?)

So, when I ran across this article in the Proceedings of the National Academy of the Sciences, I was intrigued.

Hatcheries-bred salmon are released to swim free in the ocean once they reach a certain age.  And, when that happens, the salmon change color from reddish to silver- to afford them better survival in the saltwater.  But, while they do so, these hatchery-raised salmon don’t last as long as their wild counterparts.  The bred salmon simply don’t live long enough to reproduce, and, if they do, they yield fewer baby salmon.

The logical explanation would be that these captive fish pick up a bunch of unwanted traits due to their upbringing.  It was hypothesized that being crowded in the hatchery, those that survive to be released develop alleles that accommodate the confinement.  When these salmon are in the wild, those traits actually mitigate against their survive.

Except, many of the hatcheries waters get invaded by wild-grown fish and spawn- plus, as I’ve noted above, some hatchery-grown salmon do reproduce when free.  Moreover, when hatchery and wild fish are in the same area, some of their genetic components are shared.   (Think of those plasmids that I discussed when honoring Dr. Stanley Falkow.)

So, Dr. Louis Bernatchez of the University of Laval (along with J. Le Luyer, M. Laporte [also of Laval]; T.D. Beacham, K.H. Kaukinen, R.E. Withler [of Fisheries and Oceans Canada];  plus J.S. Leong, E.B. Rondeau, and B.F. Koop [all of the University of Victoria]) effected that interesting research that was published in PNAS (link is found above).  Using cohoe salmon (released from hatcheries and wild juveniles from the same area), they examined their muscle tissues.  They found that there were no genetic differences.

But within the fishes’ epigenomes, they found significant changes.  The hatchery-raised salmon had 100 regions with different methyl groups- and 89 of them had multiple methyl groups.  More importantly, the hypermethylated regions were where immunity, locomotion, appetite, and feeding behaviors are localized.

(This is called an epigenetic change.  And, it’s not clear if such changes persist over many numbers of generations.  Epigenetics are heritable changes in the expression of genes, while the actual underlying DNA sequence remains unchanged.  We humans have many epigenetic modifications- which are influenced by our environment, our lifestyles, our age, and our disease states.  The same concept applies to fish.)

Given these changes, the research group is now examining adult fish (comparing the hatchery grown and wild grown adults; the hatchery grown fish have been marked for easy comparison). There also are plans to examine other tissue types of the fish.  For example, the transition from freshwater to ocean living requires specialized function of the gills, so if and how these tissue’s epigenetic character changes is of interest.

Obviously, while our goals of raising fish in hatcheries and let them run free so that we are maintaining our fish populations may be laudable, our artificial environments are not optimized for the fishes’ natural, free state.

Share this: