Timothy L. Hoffnagle

Parasites of native and nonnative fishes of the Little Colorado River, Grand Canyon, Arizona.

A 2-yr, seasonal, parasitological study of 1,435 fish, belonging to 4 species of native fishes and 7 species of nonnative fishes from the lower Little Colorado River (LCR) and tributary creeks, Grand Canyon, Arizona, yielded 17 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), 4 monogeneans (Gyrodactylus hoffmani, Gyrodactylus sp., Dactylogyrus extensus, and Ligictaluridus floridanus), 4 nematodes (Contracaecum sp., Eustrongylides sp., Rhabdochona sp., and Truttaedacnitis truttae), 3 cestodes (Bothriocephalus acheilognathi, Corallobothrium fimbriatum, and Megathylacoides giganteum), and 2 trematodes (Ornithodiplostomum sp. and Posthodiplostomum sp.). Rhabdochona sp. was the only adult parasite native to the LCR. Infection intensities of Ornithodiplostomum sp. and B. acheilognathi were positively correlated with length of the humpback chub Gila cypha. Adult helminths showed a high degree of host specificity, except B. acheilognathi, which was recovered from all fish species examined but was most abundant in cyprinids. Abundance of B. acheilognathi in the humpback chub was highest in the fall and lowest in the summer in both reaches of the LCR. There was no major taxonomic difference in parasite assemblages between the 2 different reaches of the river (LC1 and LC2). Parasite community diversity was very similar in humpback chub, regardless of sampling site or time. The parasite fauna of the LCR is numerically dominated by B. acheilognathi and metacercariae of Ornithodiplostomum sp. The richest and most diverse component community occurred in a nonnative species, the channel catfish Ictalurus punctatus, but infracommunity species richness was highest in a native host, humpback chub.

Experimental infection of the endangered bonytail chub (Gila elegans) with the Asian fish tapeworm (Bothriocephalus acheilognathi): impacts on survival, growth, and condition

Bothriocephalus acheilognathiYamaguti, 1934, a tapeworm known to be pathogenic to some fish species, has become established in the endangered humpback chub (Gila cypha Miller, 1964) in Grand Canyon, USA, following the tapeworms introduction into the Colorado River system. The potential impact of this tapeworm on humpback chub was studied by exposing the closely related bonytail chub (Gila elegans Baird and Girard, 1853) to the parasite under a range of conditions that included potential stressors of humpback chub in their natal waters, such as abrupt temperature change and a limited food base. Survival of infected fish under low food rations was considerably lower than that of control fish, and mortality of infected fish began 20 days earlier. Growth of infected fish was signifi- cantly reduced, and negative changes in health condition indices were found. No significant negative impacts were re- vealed from the synergistic effects between temperature shock and infection. Bothriocephalus acheilognathi does present a potential threat to humpback chub in Grand Canyon and should be considered, along with conventional con- cerns involving altered flow regimes and predation, when management decisions are made concerning conservation of this endangered species. Resume ´ : Bothriocephalus acheilognathiYamaguti, 1934, un ver plat connu comme pathogene pour certaines especes de

Run Timing, Spawn Timing, and Spawning Distribution of Hatchery- and Natural-Origin Spring Chinook Salmon in the Imnaha River, Oregon

Abstract We evaluated 16 years (1990–2005) of weir collection and spawning ground survey data to examine differences in run timing, spawn timing, and spawning distribution between naturally and hatchery-reared Chinook salmon Oncorhynchus tshawytscha in the Imnaha River, Oregon, and to look for changes in these variables over time. We compared run timing based on arrival time at the weir and found that naturally reared Chinook salmon arrived earlier than hatchery-reared fish in all 16 years. Carcasses of naturally reared fish of either or both sexes were recovered on the spawning grounds earlier than carcasses of hatchery-reared fish for all years combined and during 5 of 16 years, indicating earlier spawning by naturally reared fish. We compared spawning distribution using the percent of female carcasses recovered in each spawning ground survey reach. The percent recovery of the carcasses of naturally reared females was greater in reaches above the weir than below the weir and these carcasses were farther...

Migration Characteristics of Hatchery and Natural Spring Chinook Salmon Smolts from the Grande Ronde River Basin, Oregon, to Lower Granite Dam on the Snake River

Abstract Smolts of spring Chinook salmon Oncorhynchus tshawytscha experience substantial mortality while migrating through free-flowing reaches of the Snake River basin before reaching Lower Granite Dam, the first dam encountered in the Columbia-Snake river hydrosystem. We investigated the patterns of travel time and survival of hatchery and natural smolts fitted with passive integrated transponder (PIT) tags through specific reaches of the migration corridor during the 2000-2006 migration years for two populations originating in the Grande Ronde River basin (Lostine River and Catherine Creek). For both populations, median travel times for natural smolts were significantly longer in the upper reaches of the migration corridor but shorter in the lower reaches than for their hatchery counterparts. Also, among both hatchery and natural smolts, smaller individuals spent more time in the upper reaches, presumably feeding to attain a larger size before continuing their migration. Within populations, both hatche...

The Effect of Moderately Increased and Variable Raceway Flow Rates on Juvenile Physiology, Survival, and Adult Return of Hatchery-Reared Chinook Salmon

Abstract Increasing hatchery raceway flow to a rate similar to that seen in nature exercises salmon in the expectation that improving swimming ability will result in better survival. However, insufficient water prevents most hatcheries from fully simulating natural stream currents. We examined the effect of moderate and seasonally variable flow rates (0.25–0.75 body lengths/s) on growth and physiology of juvenile Chinook salmon Oncorhynchus tshawytscha and their ability to withstand acute stress, survive downstream migration, and return as adults. Changes in salmon growth, condition, and hematocrit followed similar patterns and did not substantially vary between treatments or cohorts. Patterns of change in plasma glucose levels were also similar for each treatment. Hepatosomatic index was higher in the 1994 cohort than in the 1995 cohort and in the exercised salmon. Liver glycogen levels were higher in the 1995 cohort. Plasma glucose and cortisol levels increased after stress and were greater in the contr...

The Influence of Size at Release on Performance of Imnaha River Chinook Salmon Hatchery Smolts

AbstractTen brood years (BYs 1988–1990 and 1992–1998) of spring–summer Chinook Salmon Oncorhynchus tshawytscha smolts that were reared at Lookingglass Fish Hatchery (Oregon) and released from the Imnaha River Weir and Acclimation Facility were evaluated to determine whether size at release affected juvenile migration survival, smolt-to-adult survival (SAS) rate, smolt-to-adult return (SAR) rate, production efficiency, age composition, straying rate, or harvest rate. Smolts were marked with adipose fin clips and were tagged with coded wire tags (all BYs) and PIT tags (BYs 1992–1998). For BYs 1992–1998, the out-migration survival rate to Lower Granite Dam (LGD) on the Snake River was greater for large smolts (30–38 g) than for small smolts (18–23 g). This juvenile survival difference did not translate to an adult survival difference, as the total (ages 3–5) and adult (ages 4–5) SAR and SAS rates did not differ between large and small smolts. Straying rates were less than 0.02% and harvest rates were less th...