PARASITES OF NATIVE AND NONNATIVE FISHES OF THE LITTLE COLORADO RIVER, GRAND CANYON, ARIZONA (original) (raw)

2004, Journal of Parasitology

A 2-year, seasonal, parasitological study of 1435 fish, belonging to 4 species of native fishes and 7 species of non-native fishes from the lower Little Colorado River (LCR) and tributary creeks, Grand Canyon, Arizona, yielded 17 (possibly 18) species of parasites. These comprised 1 myxozoan (Henneguya exilis), 2 copepods (Ergasilus arthrosis and Lernaea cyprinacea), 1 acarine (Oribatida gen. sp.), 1 piscicolid leech (Myzobdella lugubris), 3 (possibly 4) monogeneans ( Gyrodactylus hoffmani, Gyrodactylus sp., Dactylogyrus extensus, and Ligictaluridus floridanus), 4 nematodes (Contracacecum sp., Eustrongylides sp. Rhabdochona sp., Truttaedacnitis truttae), 3 cestodes (Bothriocephalus acheilognathi, Corallobothrium fimbriatum and Megathylacoides giganteum), and 2 trematodes (Ornithodiplostomum sp., Posthodiplostomum sp.). Of these, Rhabdochona sp. is the only adult parasite native to the LCR. Infection intensities (worm burden) of Ornithodiplostomum sp and B. acheilognathi were positively correlated with length of humpback chub, Gila cypha. Adult helminths showed a high degree of host specificity, the exception being B. acheilognathi, which was recovered from all fish species examined but was most abundant in cyprinids. Significantly higher abundance of B. acheilognathi in speckled dace, Rhinichthys osculus in the larger of the two creeks, Big Canyon Creek (BCC), may be related to higher population densities of dace. Abundance of B. acheilognathi in the humpback chub was highest in the fall and lowest in the summer, in both reaches of the LCR. This pattern was mirrored only partially by the tapeworms in speckled dace, and not by dace in the creeks, indicating some difference in transmission dynamics in the two fish hosts in different habitats. There were no major taxonomic differences in parasite assemblages between the two different reaches of the river (LC1 and LC2), mainly due to their connectivity, similar physical properties and, fish assemblages. Parasite community diversity was very similar in humpback chub, regardless of sampling site or time. Differences among sites (BCC, Salt Creek (SAC) , LC1 and LC2) can be related to the fish hosts present (or absent), and a result of the host specificity shown by the adult parasites. The parasite fauna of the LCR is numerically dominated by B. acheilognathi, and by the metacercariae of Ornithodiplostomum sp. The richest and most diverse component community occurred in a non-native species, the channel catfish, Ictalurus punctatus, but infracommunity species richness was highest in a native host, humpback chub. The generally species-poor native parasite fauna is due to the physical and biological characteristics of the LCR, namely the high travertine component and seasonal flooding. This in turn results in an invertebrate community which is low in species richness and diversity, as well as a species-poor native fish fauna.