9675

• UCREFRP Catalog Number: 9675
• Author: Hoffnagle, T. L. and e. al.
• Title: Parasites of Native and Non-native Fishes of the Lower Little Colorado River, Arizona - 2000 Annual Report.
• USFW Year: 2000.
• USFW - Doc Type: \
• Copyright Material: NO

Parasites of Native and Non-native Fishes of the Lower Little Colorado River, Arizona - 2000 Annual Report

by speckled dace with seven species (Mono gene a gen. sp., Ornithodiplostomum sp., B.
acheilognathi, Rhabdochona sp., Contracaecum sp., L. cyprinacea, and Acari) and humpback
chub with four species (Ornithodiplostomum sp., B. acheilognathi, Rhabdochona sp.and L.
cyprinacea) (Table 3). The remaining fishes contained three species or less and at low rates of
infection.
Of the IS species of parasites recovered, only one adult parasite, Rhabdochona sp.,
appears to be native to the Little Colorado River in Grand Canyon. This nematode was found
only in speckled dace and humpback chub but appears to mature only in speckled dace. It was
found in 11.2% of the speckled dace and in 3 of 59 (5.1 %) humpback chub examined and its
intensity of infection was also low (1-3 worms in 24 of36 infected dace). Comparisons with
other species of Rhabdochona are under way to determine if it represents a previously
undescribed species.
All other parasites found were probably introduced with non-native fishes and eight of
these are known to be or are potentially pathogenic. Some of these species may be particularly
problematic due to their life cycle and/or the native fishes that they infect. The introduced Asian
fish tapeworm (Bothriocephalus acheilognathi) was most abundant (prevalence and intensity) in
humpback chub (81.3% prevalence and up to 243 worms in one fish). Heavy infections of B.
acheilognathi may decrease growth of humpback chub, leaving them susceptible to predation for
a longer period (Hoffman and Schubert 1984; Schapperclaus 1986). Although rarely found in
general, L. cyprinacea was relatively more common in the September/October sample and was
found on 3 species of fish (humpback chub, speckled dace and plains killifish). This
ectoparasitic crustacean has been shown to be very common on humpback chub in the LCR in
previous years (Hoffnagle and Cole 1999). L. cyprinacea has been show to affect fish health,
causing changes in blood leucocyte density, loss of blood, secondary infection by
Chondrococcus, Costia and Saprolegnia and decreased growth (McNeil 1961 ; James 1968;
Bauer 1970).
Three species (Ornithodiplostomum sp., Contracaecum sp., and Eustrongylides sp.) were
recovered as larval stages. These parasites mature in fish-eating birds that may be resident or
transient in Grand Canyon. The identification of the strigeid larvae as Ornithodiplostomum sp
was confirmed and was also found in the brain and cranial cavities of three species of fish
(humpback chub, speckled dace and fathead minnow) during the 2000 sampling trips.

4

Hoffnagle et al. 2000