So, Titan has a methane sea complete with mists and islands.
How about some methane-breathing fish?
Seriously, I always thought that it was, at best, shortsighted, if not outright arrogant, to assume that life must only exist on earthlike planets. Just because we evolved breathing oxygen doesn't mean another ecology might not have produced organisms that breathe in methane gas and breathe out ethane, or something.
Or, as Jeff Goldblum's character said in Jurassic Park, "Life finds a way."