Five Things Wrong with Farmed Salmon

The pink colour of the salmon at your supermarket comes from a chemical derived from crude oil. Without it, the flesh would be grey, closer to the colour of a cod or a snapper, and nobody would buy it.

Wild salmon eat krill and shrimp, which contain a compound called astaxanthin. That is where the pink comes from. Farmed salmon do not eat krill and shrimp, so they do not have astaxanthin in their flesh, so their meat looks grey. To get them looking the way customers expect, farms add a synthetic version of astaxanthin to the feed. That synthetic version is derived from petrochemicals. Specifically, chemicals from crude oil.

That is only the second issue with farmed salmon. There are five. Let me start at the beginning.

Salmon used to come from the ocean the way you would expect. Big boats, big nets, big fish caught in the wild and brought to shore. That worked for a long time, until two things happened. The first is something called anthropogenic selection. When fishermen go out, they take the big fish and throw the small ones back. So the small ones are the ones that survive long enough to reproduce. Over generations, the genetic average of the population shifts toward smaller. Studies have shown that wild salmon are now around 20% smaller than they used to be, with life cycles about 25% shorter.

Sometimes anthropogenic selection produces something cool. In Japan, there is a crab called the Heikegani whose shell pattern looks exactly like an angry samurai face. Local fishermen would throw back any crabs that even slightly resembled a samurai, out of respect for the fallen warriors they believed those crabs represented. Over centuries, the samurai-shaped ones were the only ones reproducing. Now there is an entire species of crab in Japan that looks like a tiny samurai is staring up at you.

With salmon, anthropogenic selection produced the opposite of cool. Smaller fish meant less profit per catch. Combined with overfishing, the supply dropped. So the industry came up with what it considered a solution: salmon farms. A salmon farm is the aquatic version of factory farming. Pens or cages in coastal waters, packed with fish, fed cheap food, raised on schedule. On paper, it is logical. In practice, it has turned salmon into something I would not call healthy food. Here are the five reasons.

The diet is wrong

Salmon are what is called monogastric. They have a single-compartment stomach and do not break down food efficiently when it is not part of their natural diet. In the wild, that diet is krill and shrimp. In farms, it is whatever is cheap: soybean meal, corn, canola meal, pea meal, vegetable oils, plus "feed ingredients" and feed additives, which can mean essentially anything.

When you feed an animal a diet it did not evolve to eat, the nutrient profile of its flesh changes. In one study, researchers compared the fatty acid profile of wild salmon and farmed salmon. In wild salmon, linoleic acid, which is an omega-6 fat that becomes inflammatory at high levels, made up 1.4% of total fat. In farmed salmon, it was 14.4%. Over nine times higher. The amount humans have historically consumed is 2-3%.

It gets worse. The same study found that farmed salmon contains three times more total body fat than wild salmon. So between the higher percentage and the higher total fat, you are getting roughly 27 times more linoleic acid in farmed salmon than wild by weight.

The colour is a petrochemical

I touched on this in the opener, but the part worth repeating is that synthetic astaxanthin is not approved for human consumption in many countries on its own. It is permitted in fish feed because it is fat-soluble, which means it integrates into the salmon's tissue rather than passing through. That is what makes the flesh pink. Current US and EU reviews say the residue levels are safe. There is limited data on long-term effects. At least the way I see it, eating a fish dyed with a crude-oil derivative deserves more scrutiny than it is getting.

The microplastics

Salmon farms sit in coastal waters. Coastal waters are where most of the world's plastic waste ends up. Rivers carry bottles, packaging, and synthetic fibres from washing machines straight to those calm, shallow areas. Sunlight and waves break it all down into microscopic fragments. The fish breathe in those fragments, swallow them, and absorb them into their tissue.

In a study published in Frontiers in Environmental Science, researchers exposed isolated immune cells from Atlantic salmon to fluorescently labelled microplastic particles. Under a microscope, the cells did not just have plastic stuck to their surface. They actively engulfed it. A separate comprehensive review of microplastic contamination across multiple countries concluded that fishery products around the world are contaminated with microplastics and the toxic chemicals that hitch a ride with them.

The feed pellets themselves are part of the problem. One investigation found commercial fish feed containing up to 11,600 microplastic particles per kilogram. That is roughly the equivalent of grinding up a plastic bottle cap and mixing it into every 100 grams of feed. When you eat the fish, you eat the plastic. Microplastics have already been found in human blood and, in more recent studies, in the testicles of men. Mechanistic research shows they can cause oxidative stress and disrupt hormone signalling.

The pesticides and antibiotics

Inside a salmon farm pen, the fish are crammed in tight. According to a recent article by William Perry, single pens can hold up to 200,000 fish. That density is paradise for sea lice. The lice chew through the fish's scales and flesh. Undercover investigations of Scottish salmon farms have documented salmon with "missing eyes and large chunks of flesh and skin being eaten away by sea lice."

The industry calls these fish "pink gold" because they are so profitable. Pink gold getting eaten alive is not good for the books, so two methods are used to deal with the lice. The first is chemical baths. The fish are pumped out of the pens into "well boats," which are large ships with tanks. The water in the tanks is mixed with hydrogen peroxide or emamectin benzoate. The fish sit in the chemicals for twenty to thirty minutes, then get pumped back into the same pens they came from. The leftover water, full of lice, chemicals, mucus, and dead fish, is usually dumped straight back into the ocean.

The second is thermal delousing. The fish are pumped through a machine that flushes them with warm water, which burns the lice off. Salmon are cold-water fish. What feels like a mild bath to us feels like boiling water to them. Some die of shock or heart failure during the process. This happens every three to four weeks during peak lice season.

On top of that, the stress and crowding make the fish sick, so they are given antibiotics. Not just when they are infected. Routinely, to prevent infections from spreading through the pens. Studies have detected antibiotic residues in farmed salmon sold for human consumption. The problem with this is twofold. First, antibiotics in your food disrupt your gut bacteria, which manage almost everything that happens in your body, including (through the gut-brain axis) your mood and brain function. Second, widespread antibiotic use accelerates the evolution of resistant bacteria. A 2021 study in Aquaculture Reports found antibiotic use in Chilean salmon farms more than doubled in five years, with resistant strains becoming more common. The FDA and FAO have both warned that antibiotic resistance genes are now widespread in aquaculture environments. Norwegian salmon farms have moved to vaccines instead, which is, well, interesting, to say the least.

The genetic engineering

Here is the thing. The original problem was that wild salmon got smaller because of anthropogenic selection. There were two ways to reverse that. The slow way is to take the biggest fish, breed them, and wait generations for the average size to recover. The fast way is to genetically modify the salmon to grow bigger.

We went with the fast way. A company called AquaBounty Technologies took a growth hormone gene from Pacific Chinook salmon, which grow rapidly to large sizes, and a promoter gene from an ocean pout, which keeps the growth gene switched on year-round, and spliced them into Atlantic salmon. The result is a fish that grows faster and requires less feed.

The CEO of AquaBounty has said in an interview that the only reason they are doing this is so everyone can afford salmon. In my opinion, that claim is doing some heavy lifting. What this does to human health when consumed long-term is unknown. It could change the nutrient composition, the fatty acid balance, or introduce new allergens. The technology is too new for long-term human data to exist. And in a competitive market, once one company has a fish that grows faster on less feed, others will follow.

The defence

The industry's argument for farmed salmon is that it is a sustainable, affordable way to put protein on tables. There is something to that. Wild stocks are limited and farmed salmon does increase the supply. But the supply is contaminated. The fat profile is inflammatory. The colour is a petrochemical residue. The flesh contains microplastics and antibiotic traces. Some of it is now genetically modified with no long-term human safety data. Affordable protein is not worth much if the protein is making you sick.

What this means for you

If you have been eating salmon because you think it is healthy, the version most people are buying is closer to the opposite. The omega-6 ratio is wildly out of balance. The flesh is pink because of a crude-oil-derived chemical. The fish swam in plastic and ate plastic. They were treated with pesticides and antibiotics. And some of them are now growing faster than nature would allow because of edited genes that no one has studied in humans long-term.

What I am going to do is buy wild salmon when I can find it. Where I live, that is hard. So I will buy other wild-caught fish, or beef, or anything else where I can actually trace what the animal ate and how it was treated. I loved salmon growing up. But knowing what I know now, I am not putting it back on my plate.