Parasites and Fish Health in a Desert Stream, and Management Implications for Two Endangered Fishes

Abstract

Reintroductions of the endangered razorback sucker Xyrauchen texanus and Colorado squawfish Ptychocheilus lucius into the Verde River, Arizona, have failed to establish self‐sustaining populations. The failure of these reintroductions is often attributed to predation and competition by nonnative fishes and habitat loss, but parasite infestations (particularly a copepod, Lernaea cyprinacea) also have been implicated. We assessed the relationships among fish health, eukaryotic parasites, and bacterial and viral infections of these endangered fishes collected from two locations (Perkinsville and Childs) on the Verde River, Arizona, during February and June 1996. We also examined surrogate nonendangered native fishes (Sonora sucker Catostomus insignis, desert sucker Catostomus clarki, and roundtail chub Gila robusta) and nonnative species (common carp Cyprinus carpio and smallmouth bass Micropterus dolomieu) to determine if there were any systemwide patterns in parasite infestation and health of fishes. All tests for viruses were negative. We identified 19 bacteria (7 known fish pathogens) and 14 parasites from examined fishes. Six of the seven dominant (>10% prevalence) parasite taxa were more prevalent at Perkinsville than at Childs; Lernaea occurrence was not related to site. Time of year did not have a consistent effect on parasite prevalence across fish species, and Lernaea occurrence was not related to time of year. Lernaea cyprinacea were present on 17.3% of the 313 fish examined; 67% of the parasitized fish were infected with a single L. cyprinacea. Regression analyses on the calculated health assessment index, hematocrit, and leukocrit indicated that month, site, Trichodina, Ichthyophthirius (ich), Ornithodiplostomum and Posthodiplostomum (white grubs), and the cestode Isoglaridacris hexacotyle affected the health of fishes. However, all fishes examined were considered “healthy,” suggesting that parasites were not seriously affecting Verde River fishes. A suite of factors is likely responsible for the failure of these endangered species to reestablish.

Assessment of a Constructed Fish Migration Barrier Using Radio Telemetry and Floy Tagging

“…Predation and competition by nonnative fishes are considered as potentially serious threats to native populations of fish (Robinson et al 1998), and there are many examples where barriers have been used as control techniques to address these issues. These can include electrical barriers (), stone filled gabions (), and the use of stop logs placed in small streams (Buktenica 1997).…”

Health Assessment, Associated Metrics, and Nematode Parasitism of Rainbow Trout in the Colorado River below Glen Canyon Dam, Arizona

“…The necropsy-based technique was modified by Adams et al (1993) to provide a quantitative health assessment index (HAI) allowing statistical comparisons of data among fish populations. The Goede and Barton (1990) procedure was based primarily on data derived from salmonid fishes, but modifications of the method have been applied to coldwater and warmwater fishes (Adams et al 1993;Coughlan et al 1996;Robinson et al 1998). No consistent approach to assessment of fish health has yet emerged, and distinctions between health and condition are unclear in relation to various health assessment procedures (Goede and Barton 1990;Adams et al 1993;Coughlan et al 1996).…”

“…In contrast, a fish condition index was excluded from the HAI developed by Adams et al (1993). Robinson et al (1998) found no significant correlation between K and an HAI in seven riverine fishes.…”

“…Better condition may be reflected in greater mesenteric fat levels, which reflect long-term feeding and energy deposition (Goede and Barton 1990;Porath and Peters 1997). However, in developing HAIs, Adams et al (1993) omitted mesenteric fat levels, whereas others (Goede and Barton 1990;Coughlan et al 1996;Robinson et al 1998) examined mesenteric fat levels in health assessments.…”

“…Coughlan et al (1996) found that blood variables contributed little to health assessments of largemouth bass Micropterus salmoides. Robinson et al (1998) found no correlation between hematological variables and an HAI or condition for five fish species, but hematocrit and an HAI were positively correlated for desert suckers Catostomus clarki. Although Sutton et al (2000) examined serum lysozyme and protein in rainbow trout Oncorhynchus mykiss, blood variables were excluded from calculation of an HAI.…”