The only thing which bugs me is why did you remove the "don't duplicate random choices" check box from the fish tab? It's a very useful option because I like all my fish different.
I'd really assumed that "Don't duplicate random choices" would be the default behavior, but that's a bad idea. There should be a checkbox. Except it might be rephrased "Allow duplicate random fish."
Another minor change I would suggest is in the order of the tabs. I don't like the about window, I wouldn't like it to be the default window on the menu. I would change the order to: Settings-->Fish-->Invertebrates-->About.
Good idea.