I'll start with the good news. The chance is "very small" that the parasitic sea lice infesting farmed salmon will ever make it to your dinner plate. If a louse or two happen to sneak by, they wouldn't pose a health threat.
I'm not sure that assurance in a news report from SFGate is enough to make me want to eat salmon tonight, though, because the imagery is unsettling.
In the United States, Canada, Scotland, Norway and Chile, tiny crustaceans the size of a pea attach to salmon in farms and feed on them. These parasites were first identified by Canadian salmon farmers in the mid-'90s, and a pesticide fed to the fish controlled the lice — for a while. Eventually, the lice evolved, becoming resistant to the pesticide.
For now, the problem is concentrated in salmon farms, although sea lice do exist in the wild, too. Wild, adult salmon are sometimes caught with the parasites attached, according to the Alaska Department of Fish and Game, but they do little harm to the fish and are washed off. And, because adult salmon and juvenile salmon do not spend time together in the wild, the lice in the wild don't have an opportunity to harm the juveniles that are most vulnerable to the parasites.
Because farmed salmon live in confined areas, it's easy for the lice to find their next host when the pens are tightly packed with salmon. There's also the possibility of fish escaping the farms and introducing these evolved lice into the wild. Some salmon farms are kept close to where wild juveniles migrate, so the lice from the farms could harm juvenile wild salmon.
How sea lice do damage
Sea lice have a seven-to eight-week life cycle, and it's the final three weeks or so when they are dangerous to the salmon. That's when they suction themselves to the fish and can become lethal. They move around on the host's body, preferring to graze on the head, back and perianal areas, feasting on mucus, blood and skin, according to the Alaskan Department of Fish and Game.
The juvenile salmon get hit the hardest. Their small size and thin skin make them "lethally vulnerable" to an infestation of sea lice. Adult salmon are less vulnerable, but with juvenile salmon living in such a packed population and the infestation so dense, fewer juvenile salmon are making it to adulthood without being killed by the lice or being so badly infested they are unable to be sold on the market.
Last year, the supply of salmon fell 10 percent worldwide, and the price of farmed salmon went up as much as 50 percent in some areas.
What's being done?
Since the pesticides are no longer effective on the adaptable lice, several possible treatments are being developed, including breeding salmon for genetic resistance to the lice.
In Norway — the largest producer of farmed salmon in the world — salmon farmers are looking at closed pens that "resemble giant eggs instead of typical mesh pens." They're also using underwater drones to zap lice with lasers to kill them.
In Scotland, a device called a Thermolicer warms the water to detach the lice from the fish. In North America and Europe, salmon farmers are experimenting with adding other fish to the mix known as "cleaner fish" that will eat the lice.
Canadian-based Cooke Aquaculture, a company with salmon farms on several continents, is trying a variety of methods, including a "waterslide park for fish." The infested fish are gathered and poured into the top of a slide. As they travel down the slide, warm water cause the lice to detach. The free-from-lice salmon are then put into a clean pen.
You can see the waterslide as well as a few of the other methods Cooke is developing to tackle the parasitic sea lice problem in the video below.