Authors

P A Tierney²; J M Caffrey¹; C V Holland²;  ¹ Inland Fisheries Ireland, Ireland;  ² Trinity College Dublin, Ireland

Discussion

The role of parasites in biological invasions is becoming increasingly recognised. The differential effects of parasites on native and invasive hosts can amplify or mitigate the negative impacts of invaders on native hosts, thereby mediating the effects of invasions and altering invasion outcomes. The common dace (Leuciscus leuciscus) was first introduced to Ireland in 1886 and remained confined to a single catchment until 1980. By 2015, dace had invaded the two largest catchments in Ireland and had the highest density of all fish species in the upper River Barrow, some 200 kilometres away from the initial point of introduction. Its rapid spread has raised concerns over potential impacts on sympatric native freshwater fish, particularly given the dearth of information on its parasite fauna. In the first comprehensive study of the parasite community of invasive dace in Ireland, we compared the helminth parasite communities of long-established and recently established populations of dace with native brown trout (Salmo trutta) from the same sites. Our results show that while dace acquired acanthocephalan parasites, the parasites did not reach sexual maturity in the invasive fish. Brown trout from sites with a longer-established dace population had a lower infection burden of acanthocephalans, indicating that by taking up but not distributing infective stages of the parasite, the invasive fish may be diluting acanthocephalan infection in brown trout. However, while heavy acanthocephalan infection can cause severe damage to host fish, a decline in this dominant parasite group may alter the structure of brown trout parasite communities and disrupt native host-parasite dynamics.