My guess (though I could be wrong) would be that the 300mg and 600mg are the same quality and purity fish oils, just in different concentrations.
I would not bet on this.
I still belive you get what you pay for.
Us CrossFitters won't buy a cheap Barbell or we say the cheapest Affiliates must be bad but we will buy the cheapest Fish Oil.
Here is the test Barry Sears said to use at the seminar Saturday. Crack open enough capsules to fill 1/2 a shot glass and put it in the freezer. Pull it out 5 hours later and if you can stick a toothpick in it without much force it is of decent quality. If it is frozen he would call it sewer of the sea.
Fish as we know has a lot of poison in it, or at least that is what we have been told lately. I believe this. It is also my opinion that much of the toxins are in the oils. Just like you can sometimes smell certain foods someone eats thru their sweat.
I want the puriest, cleanest fishoil I can get for my family at a reasonable price. I know the exact numbers of every batch of fish oil I buy. I get only the 5 star rated by the IFOSprogram fishoils. I pay about .26 per capsule I take 4 a day I think the difference per day or even per year is not that great. Do we know what the side effects will be 5-10 years down the road?
Since fishoil is a supplement and not regulated I am very suspect of the purity and claims they make on their labels.
Reminds me of the All natural organic banana chips my wife bought the kids. To read the label you would think there was nothing but Bananas in the bag. As I read the ingedients it was organic bananas and organic dehydrated cane juice. I guess most people wouldn't know that is SUGAR. Natural yes but bananas have enough sugar, do they really need more.