Honestly, I bred it by mistake - and it died likely due to my research level (I'm at a 2 now) which I will remedy. I've been able to breed the Greenfin Spotanus with no issues at all, but I guess the other is a bit more finicky. Thanks for the tip!

difference between magic fish of health and magic fish of curing??

According to the messages you receive when you discover each fish:

You discovered the Magic Fish of Curing! With this fish in your tank, sick fish have a better chance of being cured.

You discovered the Magic Fish of Health! With this fish in your tank, your fish tend to be healthier.

Magic Fish List
1 - Fertility - Greenfin Spotanus
2 - Sustenance - Speckled Leaffish
3 - Curing - Crimson Comet
4 - Growth - Oriental Goldbulb
5 - Mutation - Wasp Grouper
6 - Health - Orange Snooper
7 - The Golden Guppy of Isola - Canary Fire-Arrow

The four fish that can be used to breed all other fish:
1 - Silky Shark
2 - Silky Spotanus
3 - Twin-Fin Shark
4 - Twin-Fin Spotanus

Actually, to breed all 441 possible fish you need only ANY two different ones with ANY different fin types. Thats really enough!

Actually, there are certain fins and bodies that can't be produced by breeding. They can be obtained only from eggs.

Can you give an example of ones?

The Twin-Fin is an example.

does anyone know what exactly the golden guppy does? besides sell for a lot of bucks I mean...or maybe that is why it is golden?

I wondered about twin fins! I've discovered 155 species, but have only ever seen one twin fin, my beloved twin fin fatfish.
I need the orange snooper. And I don't have any snoopers, nor have I seen one, I don't think. Of all the hours I've been playing, I only just discovered catfish and quicksilvers. I love this game!