The black-faced blenny (Tripterygion delaisi) is a small benthic fish from the family Tripterygiidae (triplefin-blennies).

It occurs at depths of 3 to 40 metres (9.8 to 131.2 ft) and lives on the substrate under large rocks, cliffs or other overhangs.

[3] Non-territorial males, females, and juveniles are cryptically coloured and are grey-brown with five dark and broad dorso-ventral bands between the head and the tail.

This signal is effected by guanine crystals in iridophores located in the stratum argentum,[9] a reflective silvery, cellular layer external to the iris.

The fish controls the brightness of its fluorescence through aggregation (brighter) and disaggregation (duller) of pigmented melanosomes in these finger-like expansions.

T. delaisi is a carnivore that mainly feeds on small crustaceans, such as Harpacticoids, Tanaidaceans, Caprellidae, and Amphipods.

[3] Over large distances the locomotion of T. delaisi can be described as anguilliform: The propulsion is caused by wavy movements of tail and body.

[3] When resting, T. delaisi lifts up the anterior part of the body and leans on the lower edge of the pectoral and on the ventral fins.

[6]⁠ The male territories are located on the lower side of overhanging cliffs and rocks and have a diameter of around 1 metre (3.3 ft).

This gesture is succeeded by slowly moving the anterior part of the body up and down (further called rearing up) if the intruder does not retreat.

This initialises a fight: The territory holder, tail-beating and all dorsal fins spread, swims towards the intruder, where they move into either a parallel or an antiparallel position.

Once it found a suitable place to spawn the wriggling movements increase in frequency and decrease in amplitude and the first dorsal fin is spread.

The male, which has either been sitting on the substrate near the female or swimming circles around her during the first phase, then moves closer and both tremble when releasing their gametes.

Fanning fresh water at the eggs for increased oxygen supply, a widely distributed behaviour in most fish families, is not displayed by T.

The main threat to T. delaisi eggs are blenniids, juvenile sparids, Crenilabrus species, crabs and sea urchins.

When accidentally plucking a hatching egg, the male swims upwards and spits the larva out, giving it a better chance of being carried away by the water currents.

[15] T. delaisi inhabits 2 disjunct areas: 1. the western Mediterranean Sea and adjacent parts of the Atlantic Oceans from north to the British Isles and south of Casablanca and Morocco, 2. western tropical Africa north to Senegal and the Macaronesian islands.

The territorial males of T. tripteronotus and T. melanurus both have a red body with a black head,[2]⁠ a signal that is strong in shallow waters where red light is still abundant, but becomes less and less striking with increasing depth due to the high absorption of long wavelengths in water.

Yellow males however, still exhibit a relatively striking colouration even at larger depths where they can successfully court for females.

The species was described in 1970 by Jean Cadenat and Jacques Blache, from a type series collected at Gorée in Senegal[21] by Michel Delais of Institut Fondamental d'Afrique Noire in Dakar, who is honoured in its specific name.