I have been taken nutrigold 75 % ratio EPA/DHA , take 2 pills a day so , 1,5gram 0,5gram DHA...most negative studies done on fish oil depression have been DHA...the positive studies are EPA
you need about 60% ratio EPA atleast to have some anti-depressant effects..and the anti-depressant effects only start afhter 3 months, so its no wonder why people dont feel a difference afhter a couple of weeks.
more then 2 gram in exccess of DHA some studies suggest is useless and is counter productive...most studies with good result suggest between 1-2grams of EPA with atleast the 60% ratio to DHA.
For my self I really noticed a difference afhter 6 months using it, not really significant but more in a subtle way im more stable and handle stresses & anxiety better then before I dont get easily over flooded like I used before.
Krill-oil is the same as fish oil basically only more bio-avaible (like 35%) so you need less, but if you do the math the fishoil is still better in comparison to the price
As said before this is never a replacement of therapy or medication, but a nice add-on to increase the effects of therapy and anti-depressants, I would also advice to use high vitamin D supplements 3000-5000IU to increase the anti-depressants workings, also works on the serotine/dopamine parts in the brain.