This is a honeycomb cowfish. Its a relative of the puffers and boxfish but gets its name from the horns (obviously enough)....the pattern easily gives away the reason for the honeycomb part too. As this is a night photo you get a bit clearer impression of the blue accents than you would in the day and you can also make out the under carriage horns on this one.
These guys probably top out at just over a foot long and spend their time grazing the reef for things like tubeworms and other invertebrates. What will probably surprise you is that all the locals throughout the region reckon these guys are the best eating fish in the sea. Apparently they are remarkably delicious roasted.