Transmission of parasites from introduced tilapias: a new threat to endemic Malagasy ichthyofauna

Invasive species are a major threat to biodiversity. In Madagascar, one quarter of freshwater fish fauna consist of introduced species. The introduction of non-native species affects native biota by means of direct interactions but also through indirect interactions including those mediated by parasites, as parasites are usually co-introduced with their hosts. Almost nothing is known about the parasites co-introduced with their fish hosts into Madagascar and their potential impact on native endemic fish fauna. We studied the metazoan parasites of native and introduced cichlid fishes (and some non-cichlids) in the northern part of Madagascar. Using parasite data we evaluated the effect of fish introduced from mainland Africa on native Malagasy cichlid fauna. We documented the co-introduction into Madagascar of parasite species from mainland Africa and also probably from Eurasia. Malagasy cichlids and some other species living in sympatry with non-native cichlids acted as competent hosts for generalist parasites and also for host-specific parasites of African mainland cichlids. However, African mainland cichlids were not susceptible to infection by parasites specific to Malagasy cichlids. The different compositions of parasite communities and infection parameters in endemic and non-native cichlids in the regions investigated may be potentially explained by the different sources and timings of fish introductions. In addition, native endemic parasite fauna even seem to be outcompeted by introduced parasites, which cross the barriers of host specificity. The transmission of non-native parasites associated with the introduction of non-native freshwater fishes may represent a serious risk to endemic freshwater fish and parasite fauna in Madagascar.