Head and lateral line erosion

Head and lateral line erosion, (HLLE) or hole-in-the-head (HITH) is a disease in fish.

HLLE begins as small pits of receding epithelium (skin) around the fish's head and/or lateral line, and sometimes onto the unpaired fins.

Rarely fatal, it does cause disfigurement, making the fish less suitable for public aquarium display.

In marine fish, two studies point to the use of activated carbon in closed aquarium ecosystems as contributors.

[2] [3] Hole in the head can be reversed by removing all activated carbon and conducting large percentage water changes.