If you're looking to max out on omega-3s, head for the fattier fish. Salmon, herring, kippers and sardines have the most. Salmon is the fish richest in omega-3 fatty acids.

Benefits of omega-3 fatty acids are: enhanced fat loss, muscle growth and joint recovery, just to name a few.

Compared with Tuna, Sardines are cheaper, have more omega-3 fatty acids, have less sodium and a better balance of sodium and potassium (good for blood pressure), and include the whole fish, so you get bonuses like a ton of calcium and iron. Some sardines are naturally far fattier than others. Fish from colder waters need the extra fat to keep from freezing.

The major choice is fish in water vs. fish in oil. And that's really no choice. Even if you drain the can, the oil adds about a third of the fat and calories.

And while you might be tempted to pay the extra for a can of fish in olive oil, don't waste your money. Make your own (just add some olive oil you have at home to a fish in water.

Toxic Mercury

Seafood is often touted as the best source of omega-3 fatty acids, key nutrients that keep hearts and brains healthy.

The risk comes from toxins like PCBs (Polychlorinated biphenyls) and mercury that are present in a variety of fish, even popular types served in restaurants and sold in supermarkets. Fish can take in toxins by living in polluted water. But many large fish, like tuna and swordfish, accumulate toxins over their lifetime by eating smaller fish and ingesting their toxins as well as their own.

Knowing which fish to eat is especially important for women who are pregnant, nursing or of child-bearing age, because the small bodies of children are easily overwhelmed by toxins, which can slow brain development. The Food and Drug Administration recommends that pregnant women not eat any swordfish, king mackerel, shark or tilefish.

Mercury and PCBs have many similar effects on the human body. Mercury kills nerve cells because it is easily transported across the blood-brain barrier that keeps many contaminants out of brain. Slower reflexes, poorer vision and coordination are sometimes seen in people who have ingested small amounts of mercury. More severe symptoms include fatigue, memory loss and nausea. Children with high levels of mercury may have mood changes, withdraw socially and have memory difficulties.

One recent study showed there is cause for concern among people who eat fish regularly. In a study published in last November's Environmental Health Perspectives, a San Francisco doctor surveyed 720 of her patients for a year and tested the blood of 116 patients who reported eating fish more than twice a week. Of that group, 63 patients had twice the Environmental Protection Agency's recommended levels of mercury in their blood. Nineteen patients were quadruple the limit and four patients had 10 times more mercury than was considered safe. One 7-year-old boy who ate canned tuna, mackerel and fresh tuna regularly had 15 times the EPA's level.

Patients with elevated mercury levels in the study often had symptoms of depression, irritability, headaches, tremors, numbness and tingling in hands and feet.

So how can you protect yourself from pollution?

Studies show the safest seafoods are farmed and wild salmon, oysters, shrimp, farm-raised channel catfish, farm-raised rainbow trout, flounder, perch, tilapia, scallop, clams, and red swamp crayfish. These fish can be eaten more than once a week, according to Santerre.

Canned tuna, crab, cod, mahi-mahi, haddock, whitefish, herring and spiny lobster have slightly higher levels of mercury and should be limited to once a week. Pregnant or nursing women should limit themselves to no more than a half pound of tuna a week.

Some seafood should be eaten only once a month: tuna steaks, red snapper, orange roughy, Pollack, halibut, northern lobster, marlin, moonfish, saltwater bass, wild trout, bluefish, grouper, croaker and sablefish. If a pregnant or nursing woman eats halibut, she should wait another month before eating another fish in this group.

And while studies show that some fresh salmon is contaminated with highly toxic PCBs, all the salmon that's canned for sale in the U.S. comes from Alaskan waters, where PCBs aren't a problem.

For bodybuilders - What's the better fish - tuna or salmon?

Canned light tuna has fewer calories, less total fat and more protein than fresh salmon. It's also a little richer in critical amino acids, like branched-chain amino acids (BCAAs), arginine and glutamine; has about twice the iron, selenium and niacin (vitamin B3); and slightly more zinc than salmon.

Fresh salmon, however, is much richer in the essential omega-3 fatty acids, with more than seven times the amount found in canned tuna. Fresh salmon also contains about seven times the folate, more than twice the vitamin B6 and slightly more vitamin B12.

Each fish clearly is loaded with nutritional benefits, so the question becomes not which fish to eat (both should be a part of your diet), but rather when to eat each for best results.

For meals before or after workouts, canned light tuna is still king. The greater protein content and lower fat levels mean this food source will deliver its critical amino acids to muscles quickly to better stimulate growth. Eating salmon around workout time is a bad idea because the healthy fats will slow down digestion of its protein. Since you still need to get in your omega-3s, choose salmon for at least three meals per week on rest days or for meals that aren't within four hours of workouts.