When a person buys fish oil from trapping supply companies, do you think it varies much in the type of fish used to make it? I don't know how fussy critters would be though.

Yes, sometimes the higher quality ones tell you what is in it though.

from every thing ive read the best are catfish ,spoon bill and trout all sun rendered as far as pressed goes salmon, menhaden or your drug store alternative cod liver oil. which by the way is also the most exspensive if you compare volume to volume. price will usually tell you which is the premium stuff good clean sun rendered fish oil is hard to make.

On your pressed fish oils, I don't recommend buying them until you can smell them. The pressed fish oils many times come in 55 gallon drums. If the drum has oil left in it after some has been drawn out, then the remaining oil in the drum will begin to oxidize. The more air in the drum, the more this affects the oil. It becomes a rancid type smell after a while, and not a fresh fish smelling oil. It only takes a whiff to notice it.

I know exactly what your saying. In the pet section of a lot of big box stores they sell pressed salmon oil. it takes on a soured smell, or more of a old oil smell!

Curious how a person would know if it's pressed, sun rendered, etc...Or if that makes much of a difference.

I know very easily. If you have been exposed to them or smelled and looked at them individually it is an easy comparison. I liken the pressed fish oils to linseed oil that is used in making paints in years past. The smell is similar to some of the lower grade pressed fish oils.

Most fish oils that are sold are usually labeled as to what they are. The smell is quite different.