This is a fluorescent fish video.
From Biomed Central:
Scientists have discovered that certain fish are capable of glowing red. Research published today in BMC Ecology includes striking images of fish fluorescing vivid red light. …
The authors identified at least 32 reef fish species belonging to 16 genera in 5 families that fluoresced visibly in red. Because the light is coming from the fish themselves and not filtering down from the surface, the red glow remains visible at depth and is easily seen at close distances.