Evolution is often thought of as a solely long-term process. But the conception that its effects are only seen after millions of years ignores a crucial part of the evolutionary process: adaptation. Because we tend to fixate on the drastic changes caused by evolution over huge timescales, it’s easy to ignore the small variations between generations that add together over time to form the big evolutionary changes we focus on. This unintentional side-lining of small adaptations can blind us to the ways in which humans are directly affecting the evolutionary processes of nature. From tuskless elephants to fish that can’t smell, animals are developing specialized adaptations to allow them to live in ecosystems that have been disrupted and altered by mankind. These adaptations are one step in the evolutionary process that already bears the unmistakable marks of humanity’s influence.
Just as humans are changing the planet, they’re changing the fauna that inhabit it. Here are some examples of how.
If you’re not particularly salmon savvy you may be under the impression that “salmon” is an individual species of fish, like how a black bear is an individual species of bear. That, however, is not true of our fishy friends. In fact, there are two main divisions of salmon: Atlantic and Pacific.
Atlantic salmon are big fish found in the northern Atlantic Ocean weighing 8-12 pounds when fully grown. Their meat is known to taste very mild and is generally cheaper than other types of salmon, due to the fact that nearly all of the Atlantic salmon commercially available today is farmed.
Climate change, human colonization, habitat destruction, and overfishing have decimated the wild populations of Atlantic salmon that were once abundant throughout the northern Atlantic. Lake Ontario was once home to this fish, but by 1900 the population was completely extinct. While there are still wild Atlantic Salmon alive and swimming, their capture is strictly regulated, hence the need for fish farms to fill this void.
What about Pacific salmon? Well, its name is a misnomer, since there isn’t one species of fish called Pacific salmon, but rather seven different species of salmon who live in the pacific: Sockeye, Chinook, masu (found mainly near East Asia), pink, Coho and Chum. While the Pacific salmons have suffered population losses due to humans and climate change, their numbers haven’t been decimated to the extent of the Atlantic salmon, so, wild-caught Pacific salmons are still commercially available.
Chinook (also called King) salmon are the largest of the Pacific salmons, weighing between 20 and 135 pounds. They’re known for being fatty, making them of value to chefs, and also quite pricey, due to their general rarity amongst fish. If you’re after something a little cheaper but still fat-filled, the Coho might be for you. At roughly 20 pounds in size, it is often cooked whole. Your low-fat salmon options include the lesser-known Chum or pink salmons, both quite small and low in fat, as well as the well-known, medium-sized, and bright pink Sockeye.
Whichever type of salmon you choose to eat though, you’ll want to find out where it was caught and whether it was farm-raised or wild-caught. Not for culinary purposes, since at least one study found that farmed salmon was as acceptable to eaters as wild salmon, but rather for health ones.
Quiteafewstudieshaveexaminedthelevels of contaminants like PCBs (polychlorinated biphenyls), PBDEs (polybrominated diphenylethers), PAHs (polycyclic aromatic hydrocarbons) and mercury, and the results have not been confidence inspiring.
A 2001 study found that farmed salmon showed higher levels of PCBs, PBDEs, DLCs (dioxin-like compounds) and other chlorine-containing pesticides that pose significant health risks to humans. Similarly, a 2004 study found high levels of organochlorine contaminants in farmed fish and found that farmed salmon originating in Europe had much higher contaminant concentrations than salmon originating in North America or Chile.
The contaminants seem to get into the salmon through their food. Commercially available salmon feeds are extremely high in contaminants like PCBs and PBDEs, likely due to being made from small fish who themselves harbour high concentrations of contamination.
Interestingly enough, mercury, the contaminant we are used to hearing about in fish, is not an issue for either wild or farmed salmon. One study found that there’s less mercury in B.C. raised salmon than other foods like eggs, honey or vegetables.
Severalstudieshave found that as few as one meal per month of farmed Atlantic salmon can expose the eater to contaminant levels that exceed those set by governing bodies like the World Health Organization. To reach a similar level of contamination by eating wild-caught salmon alone would take more than 4-16 meals per month. You can see a representative chart of this data (based on the United States Environmental Protections Agency’s guidelines) below.
Fish farms can also have devastating environmental consequences due to antibiotic use, waste accumulation, disease spread, escaped fish and more. These effects are bad not only for the surrounding oceans but for the fish too. Infections like sea lice can cause fish extreme pain or even kill them, and the genetic disorders common in farmed fish like curved spines or malformed jaws can severely harm their welfare.
So, what does this all mean for those who feed on fish?
You should keep in mind the potential risks of eating farm-raised salmon while grocery shopping and remember that you can minimize your exposure to these contaminants by choosing salmon that is either wild-caught or farm-raised in North America whenever possible.
If you’re eating salmon mainly for the omega-3 fatty acids, I have some good news and some bad news. The good news is that there are several non-meat sources of omega-3s, such as flax, chia, and hemp seeds, flaxseed oil, and eggs. The bad news is that many of the supposed health benefits of omega-3s have been largely overblown. Our own Dr. Christopher Labos has writtenabout omega-3’s ineffectiveness in preventing cardiovascular events and quite a few Cochrane reviews have found no benefits from fish oil for many conditions including ulcerative colitis, asthma, Crohn’s disease, allergies in children and dementia.
Our bodies and fishes’ (yes, fishes is a grammatically correct plural form of fish) bodies as well need water. Without it, the chemical reactions that take place constantly in our bodies would have no solvent and we would die.
Nonetheless, it seems silly that an underwater creature should have to drink. Can’t they just, I don’t know, absorb it or something?
Fish do absorb water through their skin and gills in a process called osmosis. Osmosis is the flow of water across membranes from areas of low concentration of dissolved things (solutes) to areas of high concentration. It serves to equalize the concentrations in the two areas.
In the case of freshwater fish, their blood and bodily fluids are much saltier than the water they swim in, so water will flow in through their gills. The opposite is true for saltwater fish.
As well as getting water through osmosis, saltwater fish need to purposefully drink water in order to get enough into their systems. Where their freshwater counterparts direct all of the water that comes into their mouths out through their gills, saltwater fish direct some into their digestive tract.
But fishes’ bodies, just like ours, need a certain concentration of salt to function best. They can’t just allow the water to diffuse freely through their gills; the saltwater fish would shrivel up and the freshwater fish would explode!
To stop the exploding fish phenomenon, their gills have special cells that selectively pump salt in, or out of their blood. In freshwater fish, the cells constantly pump salt in, and in saltwater fish, they constantly pump salt out. Saltwater fishes’ kidneys also help to filter out some of their salt.
Want to see osmosis for yourself? Submerge some potato slices in salt or fresh water overnight. The saltwater-soaked ones will still be crunchy, but the freshwater ones, having absorbed water, will be softer.
In short: some, but not all, fish drink. Kind of like how some, but not all, fish… fart.
So, keep in mind that next time you’re preparing your fishes’ tank you’re not only creating his environment but his beverages too.