Fish in upper left of image.
Sadly decreased Sunfish. Seen by local fisho the previous day floundering in shallow water, but the region is too dangerous to enter. Another fisho said he'd seen them washed up before. He'd lived here over 50 years.
Measured at 2.7m x 2.2m
Spanish Garden Dive, Mergui Archipelago, Myanmar
Last photo is of the hole that it went into. Put it's head in about 10cm to check, and then went in tail first. Followed it for 10-15 metres before it went into burrow.