From the Super Mario Wiki
A set of Bulbers
swimming in the water.
Bulbers are anglerfish-like enemies that appear in New Super Mario Bros. Wii. They only appear in World 8-4, having the same function as the Jellybeams. Bulbers swim freely in the water, illuminating the area around them. They can be defeated by attacking them with a fireball, by freezing them or by running into them with a Starman, although this is not necessary and perhaps even detrimental due to loss of illumination. Bulbers are very passive and will only hurt Mario if he touches them.
Bulbers reappear in New Super Mario Bros U where they act exactly like the prequel, they appear alongside Jellybeam in Deepsea Ruins of the Soda Jungle. However, they come after the Jellybeams this time.