How exactly does it work? Do you need to use it in order to get a certain fin type? I have ALL crossbreeds for all fin types EXCEPT that particular one (the one where there are NO FINS) ... so how does it work? I tried it once in my sell tank but only ONE fish changed body type ... not fin type ... it is pretty expensive for THAT kind of response!! Up to now, I've done it all on my own, not glancing at anyone else's charts, but until I find an answer, I'm pretty much at a standstill... HELP!!

mutation is random

Yes mutation is random. It may affect one fish or maybe more.

Well you have several questions:

1.How does it work: You just drop it into the tank that has the fish(s) you want to try and change. (Yes I know you already know that, but you did ask.
2.Do you need to use it in order to get a certain fin type?: No. You do not need to use the ML to get all of the fin and body types. There are some body/fin types that you can only get from eggs or by using the ML. But again you can get them from eggs so the ML is not necessary. But it can be helpful.
3.How does it work: Not that question again? LOL Well it only works on certain body types and certain fin types. I'll let you figure out what it works on and what it doesn't. And it is, as the others have said, completely random. My suggestion is to load up a tank with as many different fish that you have and drop a dose in and record what happens. Do that enough times and you will see a pattern develop.

I hope I answered all of your questions.

Mistake removed.

Sorry the spoiler was wrong. The hint should be: Combine a Lvl 2 and a Lvl 1 fin to make a Finless fish
and the answer should be: Combine a Flagged fish and a Twin-Fin fish to make a Great-Sail fish

Note from LadyCFII: Part of this spoiler is incorrect, as well.

Hi VI, Fish tycoon is a really good game and it seems to me you are an expert just a quick question about the ML you mentioned a pattern do you mean that is has the same affect on the same fish cause you also mentioned its random does it turn hyperthetically will change a spotus into fruit fish all the time or say a twin fin into a greenfin
I gather by random you mean it may effect 1 fish this time and 6 fish next time
Hope you can understand this cause it seemed a bit criptic when I read it back
Thanx and I hope you get this message cause I'm not sure if you will read this topic again

The results of using Mutation Liquid are "random in a predictable sort of way."

It is random which (or how many) fish it will affect when you drop it in the tank, as well as whether it will affect the fin or the body of each fish that is mutated. However, there are only two possibilities for each mutation. For example, if the body of a Fruitfish is changed, it will become either a Fire-Arrow or a Flashfish (and nothing else). To see exactly what the possibilities are, you can do a lot of mutations and track them, or you can refer to some of the spoiler charts that other have already created, which are in the Fish Tycoon Guide section.

Thanks SH and all ... I created my own chart for all the fin types already and didn't find any crosses to make finless, and haven't come across ANY even after 737 real hours played, after creating and selling 1441 fish, and finding 236 species .... unless my chart is wrong it looks like you have to either purchase the eggs in the store or try to mutate in order to get your first finless, right? (kinda like the same deal in PT eh? LOL)

You can breed a finless fishie, but there is only one combination of fins that will produce it (that doesn't involve having a finless already).