Parasites gained: alien parasites switching to native hosts.

Three parasitic copepods new to the well-studied Mediterranean fauna are reported. Two of them, Mitrapus oblongus (Pillai, 1964) and Clavellisa ilishae Pillai, 1962, are of Indo-Pacific origin and are considered here to have co-invaded the Mediterranean through the Suez Canal on Erythrean (Red Sea) immigrant hosts. Both are reported here from native Mediterranean clupeid fish hosts; this is the first evidence of host switching of any metazoan parasites from Erythrean immigrants to native fish hosts. The third parasite, Nothobomolochus fradei Marques, 1965, was previously known from the Gulf of Guinea and the Arabian Gulf. Possible explanations of its presence on clupeid hosts in Egyptian waters off Alexandria are discussed. The parasite utilizes an Erythrean immigrant clupeid and a native Mediterranean species as hosts. This account provides evidence of parasite and host faunal mixing on an unexpected scale.