Ok, I'm a fairly new one here and I get most of everything, but Im at level 2 advertising and when I go to price and sell my fish it seems that some fish wont sell for even the recomended price while others will sell for much more. Why? Maybe Im just being an idiot but...

Sometimes it just takes some trial and error to discover exactly the right pricing strategy. Level 2 isn't the best advertising level that you can have. Once you get all of the tank ornaments and Level 3 of advertising research, selling will get a lot easier.