Me too, I think probably it is Lepadogaster lepadogaster.

gracias Roberto, ciao

ciao Roberto, it can be Lepadogaster purpurea ?

Yes, it could be Lepadogaster purpurea or it could be Lepadogaster lepadogaster.
Few years ago Lepadogaster purpurea was not a valid species for which I had not considered but you are right, today it is a valid specie.
They are two very similar species, one of the few distinctive criteria are in the shape of blue spots on the head (very round for Lepadogaster purpurea and more oval and irregular for Lepadogaster lepadogaster). This photo does not have a good angle for a reliable identification: maybe this photo it is for 60% Lepadogaster lepadogaster and 40% Lepadogaster purpurea.
So the best identification today it is Lepadogaster sp.

Gracias Roberto, pues una especie que parecía sencilla de identificar y ya la han liado ;-))))

saludos