Campbell, M.C., C.A. Caldwell, T.D. Lewis, W.D. Wilson, and C.C. Gard. 2019. Non-lethal detection of Asian fish tapeworm in the federally-endangered humpback chub using a molecular screening tool. Transactions of the American Fisheries Society 148:832-842. DOI# 10.1002/tafs.10177
Abstract
The historical range of federally endangered Humpback Chub Gila cypha has diminished largely due to habitat loss and invasive species. Optimal spawning habitat exists within the Little Colorado River (LCR), however the temperatures in the LCR are also ideal for proliferation of the invasive pathogenic Asian fish tapeworm Schyzocotyle acheilognathi. The current standard for positive identification of the parasite is necropsy and visual examination of the gut via microscopy, a methodology undesirable for assessing parasitic infection in endangered fishes. A swab taken at the anogenital pore of the fish and analysed using a novel DNA primer targeting the cestode cytochrome oxidase I subunit (COI) mtDNA gene region offers a convenient non-lethal sampling methodology. To validate the non-lethal methodology, primer sensitivity (43%) and specificity (78%) were initially calculated by utilizing captive fish exposed to the parasite and comparing the results with the lethal standard (i.e., visual examination) methodology. Subsequently, we utilized this novel non-lethal methodology to address prevalence of infection and relative infection frequency within most size classes in a wild population of Humpback Chub, as well as address possible spatial patterns and mechanisms of infection. Wild Humpback Chub were screened for infections spring and fall 2015 at two locations in the Little Colorado River. Infection prevalence across study reaches for spring and fall was 19.5% (N = 159) and 6.2% (N = 292), respectively. Relative infection frequency increased in fish measuring 75 – 250 mm, and decreased in fish measuring 250 – 400+ mm. Based on these observations, juveniles and sub-adult Humpback Chub (<200 mm) may be ideal targets for anthelminthic treatment. Elevated levels of infection near the major spawning grounds of Humpback Chub promote parasitic infection, which will continue to persist without treatment or actions to control infections. Anogenital swabs, in conjunction with PCR and primer-specific identification, offers a time efficient non-lethal method to detect parasite infections in endangered fishes.