The asian needle fish. Some people keep these as aquarium pets, though I think one would need a rather large aquarium to keep them.
Photo credit here.
Sorry I've been neglectful of my Friday Fish lately; I wanted to do a big pretty cladogram for my 52nd FF post (i.e. one year of fishy goodness) but Mesquite, the phylogenetic analysis software I'm trying to use to make this cladogram is not being cooperative - it's made for really hard-core phylogenetics, and just messing around with trees is almost beneath it.