Sources : Sea-peacock

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:4-5): [] the types of fish gradually came to be known, names were established based either on a similarity to land animals or on their particular appearance or behavior or color or shape or sex. [Book 12, 6.5] Based on a similarity to land animals, such as ... ‘peacocks’, colored with various hues on the neck and back... - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.67): A sea-peacock [pavus piscis] is a marine fish, as Isidore says, so called from the peacock bird, because it resembles it in color. For as Isidore says: Its back and neck are painted in different colors. This signifies those who bear the burdens of their neighbors with manifold courage and modesty, as the Apostle commands: Bear one another's burdens. Their necks are also colored in a different color, when, from the complexity and merit of their virtues, they patiently lift up the hope of the heavens. - [Badke translation/paraphrase]