A very strange and unusual fish 3-4' long came up to us under the boat while we waited at the end of a dive.Even the local dive master had never seen anything quite like it. It examined us for a few seconds and then swam away. If you can provide more information about this species of fish, I'd be very interested.
Looking in the Peterson Field Guide to Atlantic Coast Fishes, this fish is in the Family Echeneididae, Remoras. There are eight known species, and any could be found near Belize. Probably the species is Slender Suckerfish, Phtheirichthys lineatus, described as similar to the Sharksucker, but even more slender, with a shorter snout. It is a good match for the illustration on plate 42 of the Field Guide. This must be an unusually big individual, since it looked to be over 36 in, but their size is listed as only up to 75 cm (30 in). These fish have a sucking disk on top of the head, a specialized modification of the spinous dorsal fin. The Field Guide says it is rare in our area, most often found attached to the Great Barracuda, but also reported to be free-swimming. It is also known as the Lousefish.