Some thoughts about Omega 3 fatty acids and fish oil...
What you are seeking are the Omega 3 fatty acids, not the fish oil itself. Generally, good fish sources at natural strength will require you to take three, 1-gram capsules of fish oil per day to get the study-recommended 1 gram of omega 3's.
The goal is to get over 1 gram (1,000 MG) of omega 3 Fatty acids each day, speciafically DHA and EPA, and preferrably in a 2:1 ratio of DHA to EPA. Other Omega FAs, like 6 and 9 are good as well, but they aren't the primary agents.
These Omega 3 fatty acids are also obtainable from vegetable sources, such as flax, primrose, safflower, olive, and nut oils. However, vegetable sources do not build up omega 3 fatty acids in the blood as quickly or as reliably as fish oils. As the concentrations are lowere, you will need to take more total oil to get the same amount of omega 3s. You may need to take a alrger ampount of omega 3s to have the same effective dose, and you will have to take it longer before it begins to become effective. It doesn't mean don't use vegetable choices. Just be aware and compensate.
Of the fish oils, salmon is the runaway favorite in the US, but it's also easily obtained from anchovies and cod, or any oily fish. And if you want to send someone else's kids to college, you can even buy it rendered directly from krill.
When dealing with salmon oils, wild-caught is better, as it has been shown to contain less mercury and other contaminants.
There are some "concentrated" fish oil products that have higher levels of omega 3s per gram. However, you don't know sourcing or manufacturing methods. Doesn't mean they're bad, just something to think about.
There are also weak formulations out there. Always be sure to check the serving or dosage size. If it's two, 1,000 MG capsules, it should add up to about 2/3 of a gram (666 MG) of total omega 3 fatty acids. No reason to digest more oil than you have to, as it's all fats and calories.
Best wishes,