Cooperative Fish and Wildlife Research Units Program: New Mexico
Education, Research and Technical Assistance for Managing Our Natural Resources

The federally endangered Humpback chub Gila cypha has experienced declines throughout its range due to loss of habitat and invasive fishes. However, optimal habitat within the Little Colorado River (LCR) represents an important stronghold for the largest remaining population of Humpback chub in the Colorado River basin. Unfortunately, temperatures in the LCR are also optimal for the proliferation of the invasive pathogenic Asian fish tapeworm Schyzocotyle acheilognathi. The current standard for positive identification of infection is necropsy and visual examination of the gut via microscopy, a methodology undesirable for assessing parasitic infection in endangered fishes. A novel species-specific primer targeting the cytochrome oxidase I subunit (COI) mtDNA gene region of Asian fish tapeworm was used in conjunction with swabbing of the anogenital pore as a convenient non-lethal sampling methodology to assess prevalence of infection in LCR Humpback chub. Acceptable primer sensitivity (52%) and specificity (79%) were demonstrated utilizing captive propagated Humpback Chub exposed to Asian fish tapeworm. Despite moderately-low sensitivity, the non-lethality of this methodology may offset decreased sensitivity, especially for monitoring in imperiled fish. Using the validated methodology, wild Humpback chub were screened for infections at two study reaches in the lower LCR spring and fall 2015. The infection prevalence for spring (includes all size classes) across study reaches was 19.5%. Infection prevalence in the fall sample was 6.2%. Infection frequency increased in juveniles and sub-adult fish (75-250 mm). However, infection frequency decreased in adult fish (250-400+ mm). Based on this evidence, juveniles and sub-adult Humpback chub (<200 mm) may be ideal targets for anthelminthic treatment. A combination of behavioral traits, including a predilection for feeding on zooplankton as juveniles and sub-adults and piscivory as larger adults may expose Humpback chub to Asian fish tapeworm infections at all stages in its life history. The molecular tool in conjunction with a swabbing methodology offers a time efficient, non-lethal method to detect infections in large numbers of fish within the hatchery environment and prevent continued transmission of the parasite into wild populations.