Lepidophagy

[3][13] A somewhat related behavior is found in Magosternarchus, which feed on the tails (both fin and connective tissue) of other gymnotiform knifefish.

[16] One species of fish in particular, called Roeboides prognathous, has a jaw structure that is extremely specialized for lepidophagy.

[16] Certain species of lepidophagous catfish, Pachypterus khavalchor, have digestive enzymes which help them to more readily break down the fins, eyes, scales of other fish.

[17] Perissodus microlepis cichlid fish tear off the scales of their prey as they swim past.

This is different from the behaviour of Roeboides prognatus and Exodon paradoxus, who remove scales more easily by attacking a specific part of their prey’s body called the caudal area.

[21] The species of cichilds that exhibit scale eating behaviours live in deep water with very low levels of oxygen and have had to rapidly evolve to keep up with a changing environment and lack of food.

[17] The attack behaviours and strikes that are employed to remove and eat scales have an energy cost and risk of harm to the predator.

[22] In light of this, there are also a number of advantages to consuming scales: scales are common, covering the body of most fish species, can be regrown relatively quickly by "prey" fish, are abundant and seasonally reliable, and their removal requires specific behaviours or morphological structures.

[2] Scale eating behaviour usually evolves because of lack of food and extreme environmental conditions.