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The effects of embryonic and larval exposure to environmentally relevant (ng/L) concentrations of common antidepressants, fluoxetine, sertraline, venlafaxine, and bupropion (singularly and in mixture) on C-start escape behavior were evaluated in fathead minnows (Pimephales promelas). Embryos (postfertilization until hatching) were exposed for 5 d and, after hatching, were allowed to grow in control well water until 12 d old. Similarly, posthatch fathead minnows were exposed for 12 d to these compounds. High-speed (1,000 frames/s) video recordings of escape behavior were collected and transferred to National Institutes of Health Image for frame-by-frame analysis of latency periods, escape velocities, and total escape...
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The extent and impact of introgressive hybridization was examined in the Gila robusta complex of cyprinid fishes using mitochondrial DNA (mtDNA) sequence variation. Lower Colorado River basin populations of G. robusta, G. elegans, and G. cypha exhibited distinct mtDNAs, with only limited introgression of G. elegans into G. cypha. The impact of hybridization was significant in upper Colorado River basin populations; most upper basin fishes sampled exhibited only G. cypha mtDNA haplotypes, with some individuals exhibiting mtDNA from G. elegans. The complete absence of G. robusta mtDNA, even in populations of morphologically pure G. robusta, indicates extensive introgression that predates human influence. Analysis...
The morphologically unique and endangered humpback chub, Gila cypha, is found in canyon-bound reaches of the Colorado River and its tributaries. Now limited to six isolated reproducing populations, this species is believed to have been once distributed over a large portion of the mainstem river. Because the species inhabits remote canyon areas, little is known about its spawning ecology. The largest remaining population occurs in the lower Little Colorado River (LCR) near Grand Canyon, where we conducted a three-year study of spawning ecology during spring (March-June) 1993?1995. We analyzed seasonal patterns of movement, population density, relative condition, spawning scores, and frequency of ripe condition and...
The completion in the fall of 1984 of Taylor Draw Dam on the White River, Colorado, formed Kenney Reservoir — thus impounding the last significant free-flowing tributary in the Upper Colorado River Basin. Fishes were sampled above and below the dam axis prior to closure of the dam and in the reservoir and river downstream following impoundment. While immediate effects of the dam to the ichthyofauna included blockage of upstream migration to 80 km of documented range for endangered Colorado squawfish, the reservoir also proved to have profound delayed effects on the river''s species composition. Pre-impoundment investigations in 1983–1984 showed strong domination by native species above, within, and below the...
Growth and survival of Colorado squawfish, Ptychocheilus lucius, larvae under fluctuating 18, 22, and 26 degrees C (5 degrees C diel fluctuations) and constant 18, 22, 26 degrees C, and 30 degrees C temperature conditions and ration size corresponding to 12.5, 28, 64,142, 320 brine shrimp nauplii fish(-1) day(-1) was determined from laboratory experiments. Growth was optimal at 31 degrees C and high at temperatures of 26 degrees C to 30 degrees C, at the highest food abundance. Lowest growth was under lowest food rations and highest temperatures. Growth of Colorado squawfish larvae declined substantially at temperatures < 22 degrees C. Neither growth nor survival was significantly different between fluctuating or...


    map background search result map search result map The role of introgressive hybridization in the evolution of the Gila robusta complex (Teleostei: Cyprinidae) The role of introgressive hybridization in the evolution of the Gila robusta complex (Teleostei: Cyprinidae)