I figured out how to breed the Galaxy Fish. Some of you have already posted the combo but to save everyone from going through the other guides it's right here.
GALAXY FISH = ECSTATIC DIAMOND FISH + ECSTATIC RUBY FISH.
It will take a long time to get the Galaxy Fish and you will most probably not get it for the first 10 tries.
How to get Ruby and Diamond to breed the Galaxy.
RUBY FISH = ECSTATIC GHOST FISH + ECSTATIC DEVIL FISH
DIAMOND FISH = ECSTATIC GHOST FISH + ECSTATIC ANGEL FISH
If you need more combo of how to get more of these rare fishes look up Twysted's rare fish guide.