Learning about the various types of aquaculture  setups is interesting and useful, but we’re ultimately interested in whether they can produce safe, nutritious, affordable seafood. Wild seafood can be pricey, unavailable, and of questionable merit or sustainability. Certain wild species are definitely worth pursuing – Alaskan salmon, sardines, herring, mackerel, to name a few – but there are environmental (overfishing, collateral damage to other important species, structural damage to the marine environment) and health (accumulation of heavy metals like lead and mercury, polychlorinated biphenyl/PCB, dioxin) issues that the conscious fish eater must stay abreast of. Healthy and safe farmed seafood, then, would be a welcome alternative, if it’s out there.
Okay. Let’s get down to it.
Which farmed seafood is safe to eat? Is there anything like grass-fed beef or pastured chicken available in scales or shells?
As a whole, farmed shellfish, when compared to wild shellfish, are very good bets for the simple fact that both lead very similar lives. Every marine shellfish , whether farmed or wild, spends its life in the ocean attached to something – rocks, a rope, a pillar, coral, the ocean floor. The only difference is that farmed shellfish are deliberately placed there by farmers, while wild shellfish are distributed by the hand of Poseidon (actually, the Nereids  do all the work while he gets the credit, but such is the life of a sea nymph). Most importantly, they all use the same sea water. They all obtain their food by sifting through that same sea water. Farmers don’t have to provide food. They’re not scattering corn  and soy  across the water, because it would be a waste. Shellfish, you see, are filter feeders.
That brings me to the primary concern people have with shellfish, or mollusks. “Filter feeder” just sounds bad. When we hear the phrase, we think of physical filters, the type we use in everyday life, like an air filter in a car engine or a coffee filter. Physical filters accumulate the undesirable stuff and are either cleaned, tossed, or recycled. They certainly aren’t eaten. Well, shellfish aren’t physical filters. They process toxins. They render harmful compounds inert and expel them. It’s true that if they reside in waters rich in heavy metals and industrial contaminants (like PCB or dioxins), some of those metals and contaminants will show up in the meat, but that’s true for any sea creature. In fact, shellfish are some of the safest, least contaminated farmed seafood whenever they’re tested .
They’re also extremely nutritious. Shellfish are extremely rich in vitamins and minerals. Three measly ounces of raw Pacific oyster (the bulk of which are farmed) gets you over 100% of the RDA for zinc, copper, selenium, B12, and half of the RDA for iron. For every 1.5 g of omega-3 they provide , just 0.1 g of omega-6  comes along for the ride. Bay scallops  are high in magnesium and selenium, clams are good for iron, copper, and selenium, abalone for selenium and magnesium , while the lowly sea snail gives massive amounts of magnesium (200 g of snail gives over 500 mg of magnesium; maybe they’re counting the shell?) and good amounts of selenium.
Lately, a favorite of mine has been the green-lipped mussel, shipped frozen from New Zealand. I initially got interested in this particular variety because of the research into green-lipped mussel extract as a canine arthritis treatment . Buddha isn’t arthritic, but I find this stuff fascinating. I’ve had some arthritis  in the past, and it never hurts to cover all your bases ahead of time. Besides, mussels are delicious and nutritious. The NZ green-lipped mussel gets good marks from the Monterey Bay Aquarium Seafood Watch , owing to its farmers’ sustainable practices: attach young mussels to ropes, lower the ropes into the ocean, and let nature take its course. I was also surprised to see the amount of omega-3s in these things. According to one study , 100 g of them (flesh only, no shells, frozen) comes with 1.5 g of DHA, 1.26 g of EPA, and not even half a gram of omega-6 fats.
Farmed shellfish are safe and just as nutritious as wild. If you’re worried about contamination, check the source and do some research. Always buy still living shellfish (dedicated seafood markets or Asian grocers are great places to buy live shellfish) where you can. If frozen is available, check the label and avoid imports from China, where waters are more likely to be heavily polluted .
The channel catfish is a bottom feeder, which sounds bad but doesn’t have to be. They’re just rapacious eaters, or foodies, even – a bit like hogs. If you feed them garbage and raise them in polluted waters (like occurs in Chinese catfish farms – check your labels!), you can’t really blame the species.
Farmed catfish is far fattier than wild catfish while being lower in omega-3s, but catfish has never been prized for its omega-3 content. While farmed catfish does have more omega-6 than wild – about 1.5g for every 100 g fillet, compared to around 0.22 g – most of the “added” fat in farmed is monounsaturated (5.7 g/100 g) and saturated (2.5 g/100 g) (PDF ). Not too bad, especially if you compare it to something like conventional skin-on chicken thigh, which gives you 4 g saturated fat , 6 g monounsaturated fat, and 3 g omega-6s for a 100 g serving. US catfish farmers may not be feeding their fish pristine, natural diets of bottom-dwelling crustaceans, insects, and small fish, instead opting for combinations of meat and bonemeal, bloodmeal, fishmeal, various seedmeals, corn, soy, wheat  byproducts, and vitamin/mineral supplements, but catfish seem to turn out decent fatty-acid profiles despite the departure from ancestral tradition (PDF ).
Toxin-wise, catfish farmed in the US are subject to strict standards and, according to a 2008 study, has very low levels of methyl-mercury and industrial contaminants like PCBs and dioxins. You may want to avoid the abdominal fat deposits on farmed catfish, however, as they contained somewhat elevated levels of dioxins. (PDF ) Other studies have shown conflicting results when comparing toxins levels in wild-caught and farm-raised US catfish, with some showing similar toxin levels (PDF ) and others showing big disparities  in favor of farm-raised. Either way, the toxins involved are at low enough concentrations not to cause worry, and they “appear to be dropping” in recent years.
If you like catfish, eat American farm-raised. It’s known for being a pretty bland fish (well known for deep frying in cornmeal batter and as a vehicle for sauces), but if it’s on the menu and you feel like fish… why not?
Tank-Farmed Freshwater Coho Salmon
Yes, that’s right. There is a decent farmed salmon: coho salmon raised in freshwater tanks. It’s not as magnificent as ruby-red firm-fleshed wild Alaskan sockeye, but it is low in omega-6s, fairly high in omega-3s, gets a “Best Choice” rating and makes “The Super Green List”  (good for the environment, low in PCB and mercury, high in omega-3s) from the Monterey Bay Aquarium Seafood Watch , and spends its life in carefully monitored freshwater tanks (as opposed to tightly packed coastal nets where metals and contaminants like dioxins and PCBs accumulate). The biggest health problems with farmed (Atlantic) salmon are the increased levels of omega-6 and the high levels of environmental and industrial contaminants. Freshwater farmed coho salmon avoids both. According to several sources, farmed coho salmon (and this is the regular, coastal farmed stuff, not the quality freshwater tank coho) sports a high omega-3:omega-6 ratio. A recent study (PDF ) found that a 100 g portion of raw farmed coho contained 1.42 g omega-3  and just 0.46 g omega-6 (ratio of 3.1:1), compared to wild coho’s 0.9 g omega-3 and 0.06 g omega-6 (ratio of 14:1). The ratio is way different, sure, but does it really matter, given the paltry absolute amount of omega-6? If you look at the USDA database, 100 g of raw farmed coho has 1.3 g of omega-3 and 0.3 g omega-6. Any way you cut it, farmed coho is a good source of essential fatty acids, and I’d guess that freshwater tank-farmed coho salmon is just as good as conventionally farmed coho in that regard, if not better.
As of now, there are only a few freshwater, landlocked coho salmon farms in operation: Domsea Farms , out of Washington state, which sells coho to Whole Foods and other retailers under the SweetSpring label; and Swift Aquaculture , in British Columbia, which supplies upscale restaurants. More are surely coming, though, so be on the lookout for tank-raised (not coastal) coho in your area. You’ll still want to avoid other farmed salmon , of course.
US Rainbow Trout
Most rainbow trout eaten in the United States is also farmed there, and it’s one of the better choices. It may not be a sexy, exotic fish with intense flavors and high levels of omega-3s, but it’s a solid choice with a low environmental impact, minimal levels of contaminants, and a reasonable price. You can get it fresh pretty much anywhere and know, just by the “Farmed, USA” label, that it’s safe to eat.
More so than any other farmed fish I’ve come across, the fatty acid profile of farmed trout closely resembles that of wild trout. For example, a single 100 gram fillet of farmed rainbow trout has a gram of omega-3, 0.7 g of omega-6, 150% of the B12 RDA, and a decent amount of selenium. The same amount of wild trout is extremely similar nutritionally, with the main changes being 200 mg fewer omega-3s and 500 mg fewer omega-6s.
A tropical white fish, the barramundi is the “it” fish of the moment. It’s low in overall fat, offers about 840 mg of omega-3 per 5 ounce serving, requires less wild fishmeal than other carnivorous fish, is relatively free of contaminants, lives in freshwater tanks (at least in the United States) where it can’t affect wild ocean stocks, and Dr. Oz sings its praises  (which almost makes me want to delete this section). Barramundi is okay, I guess, but it sounds rather uninteresting and bland. It’s also expensive, fetching over ten dollars a pound for frozen fillets at some markets.
Still skeptical? Listen to the barramundi evangelist talk about the fish  on NPR for an unbiased perspective. No, but seriously – by all accounts , it’s a safe farmed seafood choice with nice levels of omega-3s, so give it a shot. Or, at least, don’t fear the barramundi.
These are freshwater crustaceans and thus not seafood, but I spent many a summer catching them in New England, so I’m going to include them anyway. Crayfish are great, like tiny lobsters. Crayfish farming gets a clean bill from the Monterey Bay Aquarium, and I like that crayfish farming often means setting the little mudbugs loose in a rice paddy or pond to feed on the local flora and fauna, enrich the local habitat, and breed like mad. Farmers will sometimes supplement with feed pellets, but not always. Not a lot of meat on them, but if fully cooked they can be entirely consumed, shell and all. If you’re too squeamish to do that, you should definitely suck out the sweet contents of the head and eat the tail.
Look – if Trapper Arne’s awesome 1990s-era website  says that “crayfish is good eating,” I’m not going to argue. Stay away from imported crayfish from Asia, though; stick to farmed crayfish from the United States.
What say you? Have I gone mad? Is all farmed seafood poisonous and toxic? Have I left out your favorites? Let me hear about it.