Nonlethal Detection of Asian Fish Tapeworm in the Federally Endangered Humpback Chub Using a Molecular Screening Tool

Abstract

Optimal spawning habitat of federally endangered Humpback Chub Gila cypha exists within the Little Colorado River; however, temperatures in the Little Colorado River 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 infection in endangered fishes. A swab taken at the rectum of the fish and analyzed using a novel DNA primer targeting the cestode cytochrome oxidase I subunit mtDNA gene region offers a convenient nonlethal sampling tool. To validate the nonlethal methodology, primer sensitivity (51.9%) and specificity (79.5%) were calculated by exposing captive fish to the parasite and comparing results using the lethal standard method (i.e., visual examination). Subsequently, we utilized this nonlethal methodology to address prevalence of infection and infection frequency across a range of size‐classes in a wild population of Humpback Chub and addressed possible patterns and mechanisms of infection in the Little Colorado River. When wild Humpback Chub were screened for infection prevalence in spring 2015 (21.4%, n = 140) and fall 2015 (6.6%, n = 258), the relative frequency of infection was highest in juveniles and subadult fish (200–300 mm). Elevated levels of infection near the major spawning grounds of Humpback Chub in the Little Colorado River promote parasitic infection, which may continue to persist without treatment or actions to control infections. We demonstrated that rectal swabs, in conjunction with PCR and primer‐specific identification, offer a time‐efficient nonlethal method to detect infection of Asian fish tapeworm in an endangered fish.

Establishment of a Reproducing Population of Endangered Humpback Chub through Translocations to a Colorado River Tributary in Grand Canyon, Arizona

“…Compromised survival would be expected in the heavily parasite‐infected fish of the LCR (reviewed in Campbell et al. ). Individual growth is critical to the survival and reproductive fitness of fish, and the lack of juvenile rearing and recruitment to maturity in the colder postdam waters of the Colorado River (Robinson and Childs ; Yackulic et al.…”

“…Fish and Wildlife Service (USFWS) in Dexter, New Mexico, to reach a size that was large enough to mark with individual tags. Asian tapeworm Schyzocytyle acheilognathi is prevalent in the LCR and infects Humpback Chub (reviewed in Campbell et al 2019), so newly collected fish were quarantined and treated for common diseases and parasites. The juvenile Humpback Chub were then weighed, measured, and internally tagged with 134.2-kHz, 12.5-mm passive integrated transponder (PIT) tags.…”

“…heavily parasite-infected fish of the LCR (reviewed in Campbell et al 2019). Individual growth is critical to the survival and reproductive fitness of fish, and the lack of juvenile rearing and recruitment to maturity in the colder postdam waters of the Colorado River (Robinson and Childs 2001;Yackulic et al 2014;Van Haverbeke et al 2017) was thought to limit the population in Grand Canyon (Valdez et al 2000;Trammell et al 2012).…”

Non‐lethal detection of Eubothrium crassum (Cestoda) in farmed Atlantic salmon, Salmo salar, using anal swabs and real‐time PCR

“…Being more sensitive than conventional PCR and sequencing, the qPCR assays presented here can be used for species identification in formalin fixed samples, for example when tapeworms are detected in histological sections. As shown for humpback chub (Campbell et al, 2019), the current method can also be applied in ecological studies of wild fish, for example from endangered populations, where a non-lethal method is the only alternative. Writing -review and editing; methodology; formal analysis.…”

“…This has been applied in several studies, including tapeworm detection in terrestrial animals (Øines et al., 2014), food content determination in birds (Oehm et al., 2011) and prey identification in scats from seals (Matejusová et al., 2008). More recently, a method detecting the Asian fish tapeworm, Schyzocotyle acheilognathi , in the endangered humpback chub, Gila cypha , using rectum swabs and PCR was developed (Campbell et al., 2019).…”