Fish oil is one of the staples everyone should have in their diet. I mean, everyone. From age 2-120.
I squeeze some in for my birds, and for my cats as well when I feed them. It is the only oil that is anti-inflammatory, and contains DHA/EPA, which are the same types of fats that consist of around 90% of the brain's solid matter (brain is around 90% water. But, of the 10% that is solid, 90% of it is DHA/EPA). Highly, extremely important. Especially for young children/birds/cats/whatever that are still developing and growing their brains. Of course, on the other end of the spectrum, it's also important for preservation of our very important organ.
As well as a whole host of other health benefits: heart issues, cholesterol, hypertension, etc.
Downfall is that it takes about 6 months of consistent, daily use to see a medical change--as in blood panel.
HOWEVER, the market is flooded with many brands of cheap fish oil that cannot and absolutely should not be consumed. They claim to be microfiltered, but are never actually tested per batch for mercury and other toxin levels. They are also made from large fish (salmon, etc), which contain high levels of mercury as they are larger fish. These types of fish oils are the ones found in supermarkets such as Wholefoods brand, Trader Joe's, Costco brand, etc.
The fish oil you DO want is not from salmon, but from small fish--mackerel, anchovies, sardines, etc. It needs to be tested batch for batch for mercery levels, and other heavy metals and toxins, and it needs to contain a potent amount of DHA/EPA. Potent meaning at least 600 DHA/serving. Most brands out there have very low DHA/EPA content.
This is the brand that I use and also sell in the medical practice at which I work:
Heart Health Essential Omega Iii Fish Oil With Vitamin E - Single Bottle (30 Servings)
It meets all the requirements that I just stated. It is double-tested. Once by the distributor and once by the manufacturer. It seems expensive, but if calclated per DHA content, it's actually cheaper than a crappy Trader Joe's fish oil which gives you 200 DHA as opposed to 600 per serving. Further, it has no preservatives at all, and only has glycerin/gelatin (the capsule), water, and lemon oil as additional ingredients. It's harvested from small fish in low-polution levels in Peru.
Whatever brand you buy, these are the guidelines:
1) Made from small fish (NOT SALMON)
2) Tested. By batch. If you really want to be detailed about it, call and ask them when the last batch was pulled. If they cannot answer that, don't buy the product.
3) High DHA/EPA content (at least 600mg DHA per serving)
4) No additives.