And you shouldn't be eating canned anything... canned food is nasty stuff and the tuna has tons of mercury and other heavy metals in it.
This is an important fact to remember, unless you don't care about getting mercury poisoning. I always cringe inside when I hear a weight lifter say they eat tuna straight out of the can. Yuck.
It should also be noted that many tuna populations have sharply declined in the last few decades. They are being killed faster than they can reproduce due to industrialized fishing. Canned tuna should be avoided unless it says the fish was troll or pole-and-line caught. Most canned tuna is caught by longline or purse seine, which also kill countless sharks, turtles, birds, and other species. There are no international regulations on bycatch. ZERO. Why should we only care about dolphins? And even then, the Dolphin-safe labels are a joke. Dolphin populations have still not recovered since that whole campaign started in the 1970s. Innovations have been made to release the dolphins alive, but some of them still die in the nets and the stress the dolphins experience from being frequently chased and captured prevents them from enjoying healthy lives and reproducing normally.
Monterey Aquarium Seafood Watch- Canned Tuna
As for fish oil pills, they are made from small forage fish, such as Menhaden, which are an essential food for top marine predators. By taking so many small forage fish to make fish pills, you are literally taking food out of the mouths of the big fish.
Menhaden are also filter feeders and help to keep the water clean. Is it any surprise that there has been an increase in the number of malnourished fish, and algae blooms in our bays and canals? Where have all the Weakfish gone? Apparently into the bellies of Striped Bass which can no longer find enough Menhaden to eat.