Your vet will need to examine the whole body to see if there are any other parts that are starting to lose hair, any red or discoloured areas, any loose skin flakes or small ectoparasites.
It is probably a mutualistic arrangement as the remora can move around on the host, removing ectoparasites and looseflakes of skin, while benefiting from the protection provided by the host, and the constant flow of water across its gills.