Some species of Driftfish; Man'0'War Fish or similar? We saw a number of fish that looked similar to this tangled in Man'O'War jellies washed up on a Cuban beach many years ago.
In that more naive and innocent time period (late 1980's) I brought a number of very small fish, shrimp, crabs, etc. back from the Caribbean on several occasions, just in plastic bottles in my luggage. Almost everything survived the trip and lived well in my tanks...except these guys, every one DOA.