A few months he says.. ha!

To answer the question though the mistlands update did not include a recipe specifically for magma fish so their only use as of right now, if you can find them, is to be converted to raw fish. I would just avoid going anywhere near the ashlands in your world. If you do that then when they are released (another couple years) you won't have to start a new world to explore them.

Yeah, I'll stick to the Mistlands and the Plains. Thx!