Effects of fish species composition on Diphyllobothrium spp. infections in brown trout – is three‐spined stickleback a key species?

Abstract

Subarctic populations of brown trout (Salmo trutta) are often heavily infected with cestodes of the genus Diphyllobothrium, assumedly because of their piscivorous behaviour. This study explores possible associations between availability of fish prey and Diphyllobothrium spp. infections in lacustrine trout populations. Trout in (i) allopatry (group T); (ii) sympatry with Arctic charr (Salvelinus alpinus) (group TC); and (iii) sympatry with charr and three-spined stickleback (Gasterosteus aculeatus) (group TCS) were contrasted. Mean abundance and intensity of Diphyllobothrium spp. were higher in group TCS compared to groups TC and T. Prevalence, however, was similarly higher in groups TCS and TC compared to group T. Zero-altered negative binomial modelling identified the lowest probability of infection in group T and similar probabilities of infection in groups TC and TCS, whereas the highest intensity was predicted in group TCS. The most infected trout were from the group co-occurring with stickleback (TCS), possibly due to a higher availability of fish prey. In conclusion, our study demonstrates elevated Diphyllobothrium spp. infections in lacustrine trout populations where fish prey are available and suggests that highly available and easily caught stickleback prey may play a key role in the transmission of Diphyllobothrium spp. parasite larvae.

A simplified method to estimate Diphyllobothrium spp. infection in salmonids

“…; Kuhn et al . ). The plerocercoid larvae of D. dendriticum are significantly larger than those of D. ditremum in the fish host and hence have larger cysts that are also more irregular in shape.…”

“…Our findings suggest that the simplified methodology might work slightly better for charr than for trout. This is possibly caused by the overall tendency of charr mostly to become infected with D. ditremum through heavy zooplankton feeding, whereas trout can have high intensities of D. dendriticum mainly aggregated through piscivory (Henriksen et al 2016;Kuhn et al 2016). The plerocercoid larvae of D. dendriticum are significantly larger than those of D. ditremum in the fish host and hence have larger cysts that are also more irregular in shape.…”

“…A diverse range of Diphyllobothrium spp. infections as well as feeding ecology and piscivorous behaviour in brown trout and Arctic charr is found among these sampling sites (Eloranta, Knudsen & Amundsen 2013; S anchez-Hern andez & Amundsen 2015; Henriksen et al 2016;Kuhn et al 2016).…”

“…In large piscivorous fish, these parasites can accumulate and reach very high intensities as infected fish may function as paratenic hosts (Curtis ; Knudsen & Klemetsen ; Kuhn et al . ; Siwertsson et al . ).…”

“…copepod or fish), the parasite larva penetrates the stomach of the predatory host and become encysted primarily on the stomach and intestine (Torres, Ley an & Puga 2012). In large piscivorous fish, these parasites can accumulate and reach very high intensities as infected fish may function as paratenic hosts (Curtis 1984;Knudsen & Klemetsen 1994;Kuhn et al 2016;Siwertsson et al 2016). High intensities of Diphyllobothrium spp.…”