Glassy sweeper

This morning, as we were preparing to get out of the water toward the end our dive, we encountered a sizable school of glassy sweepers in a cave, just below the surface. We have occasionally seen one or two under ledges, but this was the biggest concentration that we have ever seen.  They hang out in dark places by day. The name is derived from the nearly transparent appearance of their juvenile stage. This species is also commonly known as "copper sweeper" and "hatchetfish". These fish were about 4 inches long.