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  Female

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  Territorial male

The black-faced blenny (Tripterygion delaisi) is a species of fish in the family Tripterygiidae, the threefin blennies. It is found in the Mediterranean Sea and adjacent Atlantic Ocean coasts, at depths from 3 to 40 metres (10 to 130 ft), and prefers shaded areas such as rock faces and crevices. During the breeding season, territorial males develop a characteristic yellow body with a black head, while females and other males are coloured grey-brown for camouflage. The black-faced blenny produces a red fluorescent signal using specialised cells in the iris, which it can regulate in brightness. Males defend nesting territories beneath overhangs, aggressively repelling intruders and defending the eggs from predators until they hatch. These black-faced blennies, one female and the other a territorial male, were photographed in Arrábida Natural Park, off the Portuguese coast.

Photograph credit: Diego Delso