Parasites and Lessepsian migration of Fistularia commersonii (Osteichthyes, Fistulariidae): shadows and light on the enemy release hypothesis

According to the enemy release hypothesis, one of the reasons for the successful establishment of nonindigenous species in a new habitat is the liberation from natural enemies, and among them the parasites. The rapid spread of the Red Sea/Indo-Pacific fish Fistularia commersonii in the Mediterranean Sea, which in just 7 years (2000–2007) invaded nearly all of the basin, gives an opportunity to study the dynamics of the host and its parasites in its recently invaded range. Information on the parasites of this fish in its original habitat is quite scarce. The present study describes the metazoan parasites of 40 specimens of F. commersonii (total length range 73–107 cm) caught in the Mediterranean Sea (Sardinia, Tunisia, Libya) from 2005 to 2015. The parasite fauna of this migrant in the recently invaded range is mainly a combination of generalist juvenile/larval species (probably acquired in the new habitat) with some of its adult natural parasites (probably co-introduced during migration). The results indicate that a non-indigenous species is not always released from its natural parasites and that its success is not simply associated with such liberation. Actually, the parasite fauna of F. commersonii increased along its migration path, acquiring new generalist species, but also conserving a subset of natural parasites. These data suggest caution in the uncritical acceptance of the enemy release hypothesis, because the different phases of the invasion process and establishment of a non-indigenous species appear to be related to a combination of ecological, physiological and behavioural factors.