Muskate hit the nail on the head! It is NOT the amount of fish oil but the amount of EPA and DHA each serving of fish oil contains. Now this will vary greatly on the quality of the products out there. Usually lower quality products or brands that cheap out will list 1-2 liquid gels(which is what is should be produced as unless using a straight up liquid like some of the other members suggested) at 1000mg of fish oil but if u look below at the EPA and DHA content it will only be at 300 or 400mg total...that in my opinion is a shitty supplement and u should NOT waste your money on it unless there is NO other alternative. Also if it doenst even list the epa/dha the likely hood its a lower quality product is pretty high.
Now A GOOD fish oil should contain anywhere from 700-1000mg epa and 300-500mg DHA per 1~2 lsoft gels. If this is the case i would suggest you take 2 soft gels with EVERY meal or at least 3 meals per day. That way your getting 1~1.5g of OMEGA 3'S in SUPPLEMENTAL form at least 3x/day. U can always get more through your diet with things like flaxseeds, flaxseed/olive oil butter, falxseed peanutbutter spread, avacados, salmon, haddock, tuna, tilapia etc, etc....
*side note if one wishes to get specifically more DHA for brain support/development and other benefits you can look for a DHA specific product. Which will usually still have some epa in it but much higher DHA which usually isnt the case. And there will be some who say DHA is more important than EPA but thats a while other arguement.
Good luck