Red-black triplefin - Tripterygion tripteronotum (Risso, 1810) - Cyprus

The red-black triplefin (Tripterygion tripteronotum) is a species of fish in the family Tripterygiidae, the threefin blennies. It is widespread in the eastern Atlantic Ocean and the Mediterranean Sea. In the Black Sea it occurs off the coasts of the Crimea and Ukraine
From https://en.wikipedia.org/wiki/Red-black_triplefin

Underwater photos  by Costas Constantinou