Let's face it, the fish counter is a bewildering place. Knowing if the fish is fresh is hard enough. And then there’s choosing between farmed and wild-caught varieties.

Is farmed fish OK for you and the environment? Should you always buy wild? It depends.

Half the seafood sold in the U.S. is farmed, and responsible aquaculture, as fish farming is known, is necessary to satisfy the world's growing appetite for seafood. But aquaculture waste can harm the environment, and escaped farmed fish can compete with, and weaken the genetics of, wild fish.

Human health is also a concern. Both farmed and wild fish can be tainted with mercury (a neurotoxin that can cause developmental problems in young children), pesticides and persistent organic pollutants (POPs), such as dioxins and polychlorinated biphenyls (PCBs). These toxins come from industrial waste that pollutes our waterways, and fish farmed in coastal waters are more likely than their wild brethren to be contaminated with POPs.

Salmon, which is one of the top three fish eaten in America, is particularly worrisome. Though it tends to be low in mercury (whether it’s farmed or wild), it may pose other risks. One study suggests farmed salmon is higher in POPs than wild salmon. Another study tied eating farmed salmon with higher rates of insulin resistance (a precursor to diabetes) and obesity in mice. In a third study, mice given farmed Atlantic salmon that had been fed soybean oil (sometimes used as a replacement for fish oil) had a higher risk of obesity. Note that all salmon labeled "Atlantic" is farmed.

As with livestock farming, farming fish also comes with concerns about antibiotic resistance (antibiotics are used to control disease and parasites).

So does all this mean you should never land farmed fish on your plate? Not if you choose wisely. Here are some tips for buying farmed seafood that's safe for the environment and your family's health.

Do your homework to choose smart farmed fish. SeafoodWatch has a downloadable app that makes it easier to identify environmentally sound wild and farmed fish that are also lower in mercury. The Environmental Defense Fund also has a Seafood Selector. Guides like these are a good place to start, but while they rate seafood for mercury content, they don't measure POPs and other pollutants.

Some smart choices for farmed fish include:

  • Striped bass (farmed is actually lower in mercury than wild)
  • Oysters
  • Clams and cockles
  • Abalone
  • Rainbow trout
  • Arctic char
  • Tilapia

Know your fishmonger. Many independent and some national retailers, such as Whole Foods and Wegmans, have their own sustainable seafood programs that mandate responsible aquaculture and fishing practices.

Ask how the fish was farmed. Not all aquaculture is created equal. Some practices are better for the environment and human health than others. For example, salmon farmed in enclosed recirculating tanks is a better option than salmon farmed in ocean pens, according to SeafoodWatch.

Eat low on the food chain. All fish can be exposed to mercury and POPs, but larger fish that feed on smaller ones are more likely to accumulate these toxins. And little fish can offer big nutrition. For example, anchovies and sardines, which are always wild-caught, are rich in heart-healthy omega-3 fatty acids.

Farmed or wild, enjoy a variety of fish. In general, Americans aren't very adventuresome when it comes to seafood. Shrimp, canned tuna and salmon account for more than half the fish we eat each year. And when we think of healthful seafood, many of us think of salmon. But other varieties offer just as much or more in the way of omega-3 fats. Try black cod, herring, mackerel and of course those little anchovies and sardines. Arctic char and rainbow trout, both of which are related to salmon and farmed responsibly, are also good options.

Alison Ashton is a freelance food writer, recipe developer and Cordon Bleu-trained chef based on Los Angeles.