A pughead skeletal deformity is where the entire top jaw is compressed downward, which ends up making the bottom jaw look like it is pushed outward.  While pughead skeletal deformities are more common in captive fish, this condition is relatively rare in wild fish. In captive populations, this condition is typically attributed to “chemical contaminants, dietary limitations or excesses, temperature variations during larval development, and inbreeding.”

According to Francini-Filho  and Amado-Filho, the two scientists who reported this abnormality in the journal Coral Reefs, this is the first recorded incident of pughead skeletal deformity reported in Queen Angelfish and in the family Pomacanthidae.

During a diving trip between May 24 and June 8, 2011, they found two Queen Angelfish, Holacanthus ciliaris, while at St. Peter and St. Paul Archipelago, Mid Atlantic Ridge, Brazil. Both fish were large, ranging from 30 to 35 cm in length (12-14 inches) and appeared healthy with the exception of the pughead skeletal deformity. Given that inbreeding and low genetic connectivity are already reported for this species in St. Peter and St. Paul Archipelago, Francini-Filho and Amado-Filho both believe this is what caused the abnormality.