Translocations of tropical and subtropical marine fish species into the Mediterranean. A case study based on Siganus virgatus (Teleostei: Siganidae)

About 160 exotic fish species are documented from the Mediterranean Sea (MED). A relatively small but rapidly increasing percentage of these non-indigenous species is represented by tropical or subtropical fishes which are naturally not distributed in a sea adjacent to the MED. The occurrence of these species is mainly ascribed to shipping traffic and aquarium trade as they are not able to actively arrive at the MED via the Suez Canal or the Strait of Gibraltar. During a survey of siganid fishes at the Natural History Museum in Vienna, a single specimen of the Barhead spinefoot, Signs virgatus that had been captured in 1975 in the Adriatic Sea was found. It represents the first record of this species for the MED. It is also one of the earliest confirmed records of the introduction of a tropical fish species into the MED and anexample of a drastically translocated species (DTS). Nearly all records of drastically translocated fish species (DTFS) were just published this century, although one record dates back to the 19th century. A rapid increase of such translocations into the MED has been observed since 2010. The rising water temperatures caused by climate change increases the probability that such species will establish self-sustaining populations in the MED. A first compilation of DTFS into the MED is presented. Characters distinguishing S. virgatus from the closely related sister species S. doliatus, as well as from the
Lessepsian migrants S. luridus and S. rivulatus, are given.