A photo sent to me by Luisa Delgado in Bucharest. A bit of a long way for an Australian entomology group, but I still managed to ID it. 

The Argulidae are parasitic crustaceans of uncertain affiliation. They seem to be pretty ‘primitive’ but the complete lack of a fossil record doesn’t help. 

Fish lice can be a few millimetres in size to over 30mm long, although the females tend to be larger than the males. Almost all are ectoparasites on fish, with a few on invertebrates or on amphibians. The body is generally oval and flattened, covered by the carapace. Their eyes are prominent as in the photo, and the attach themselves to the host with mouthparts and antennae modified to form a hooked, spiny, sucker-bearing proboscis. They can also swim when not attached to a host, which probably explains the need for eyes. They leave their hosts for up to three weeks to mate and lay eggs, then seek a new host and  feed on mucus, sloughed-off scales, or blood. The larvae are also parasitic.