I've dissected SHITLOADS of critters both for my Biology-heavy Fisheries Management degree, and for subsequent employment.
The most interesting was a mink (good way to use the by=products of fur farming since no one eats weasels). The professor proclaimed that my dissection was surgically neat, lol.
The ones I've done the most of are Pacific codfish, to do stomach-contents checks and take otoliths (ear bones) for ageing purposes.
It is a very important learning tool if you are doing it with well-educated guidance. Otherwise you're just hacking shit up.