The prevalence of infection and susceptibility of the aquatic oligochaete Tubifex tubifex to Myxobolus cerebralis, was examined in 2 studies on the upper Colorado River, Colorado, USA, where whirling disease occurs in wild trout populations. In the first study, the prevalence of infection ranged from 0.4 to 1.5%, as determined by counting the number of T. tubifex releasing triactinomyxons of M. cerebralis directly following their collection from the field. The susceptibility of those T. tubifex not releasing triactinomyxons was assessed by the number of these oligochaetes releasing triactinomyxons 3 mo following experimental exposures to spores of M. cerebralis. The prevalence of infection following experimental exposures of these T. tubifex ranged from 4.2 to 14.1%. In a second study, all T. tubifex collected at 2 different times directly from the 2 field sites in Colorado were exposed to spores of M. cerebralis. Individual oligochaetes representing those groups of T. tubifex releasing and those groups not releasing triactinomyxons at 3 mo were screened with molecular genetic markers. T. tubifex populations found at the 2 study sites consisted of 4 genetically distinct lineages that varied with respect to their susceptibility to experimental exposure to M. cerebralis. Lineages I and III contained the most oligochaetes susceptible to M. cerebralis and were the most prominent lineages at Windy Gap Reservoir, a site of high infectivity for wild rainbow trout on the upper Colorado River. In contrast, at the Breeze Bridge site which is below Windy Gap Reservoir and where M. cerebralis infections are less severe in wild trout, oligochaetes in lineages V and VI that are resistant to M. cerebralis were more prominent. These results suggest that certain habitats, such as Windy Gap Reservoir, are conducive to large and more homogenous populations of susceptible T. tubifex lineages that may serve as point sources of infection for M. cerebralis. Although not a direct objective of this study, there was no evidence of M. cerebralis infections among any oligochaetes other than those that would be classified as T. tubifex by standard morphological characteristics. KEY WORDS: Whirling disease · Myxobolus cerebralis · Tubifex tubifex Resale or republication not permitted without written consent of the publisherDis Aquat Org 51: [113][114][115][116][117][118][119][120][121] 2002 clines among wild rainbow trout populations in the states of Idaho, Montana, Colorado and Utah, USA (Nehring & Walker 1996, Vincent 1996, Hedrick et al. 1998. M. cerebralis is the best known of 1300 parasites grouped in the phylum Myxozoa and the first shown to possess a 2 host life cycle including salmonid fish and an aquatic oligochaete, Tubifex tubifex (Markiw & Wolf 1983, Wolf & Markiw 1984, Wolf et al. 1986). The parasite has been observed among wild fish in 23 states in the USA, but without the same disastrous effects observed in the intermountain west (Nickum 1999). The differences in the impacts on wild fish between geographic region...

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Replicate samples of tardigrades were collected at six altitudes from five mountains on Vancouver Island, British Columbia, Canada, to determine the relationship between species of tardigrades and altitude, and between species of tardigrades and species of mosses in which they were collected. A total of 13 696 tardigrades representing 39 species were collected and identified. Thirty-seven species of mosses were identified. Data were analyzed using principal components analysis and cluster analysis. The results from both multivariate statistical methods indicated that the distribution and abundance of tardigrades were not dependent upon the altitude or moss species.

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Thirty-one species of eutardigrades were collected on five mountains on Vancouver Island, British Columbia, during July 1986 and July 1987. Three of the species found were new to science, including 1 species, Platicrista cheleusis n.sp., described herein and 2 species described elsewhere, and 21 others are new to British Columbia; 13 of these are also new to Canada.

Some specimens of Chaetogaster diastrophus may have dorsal seatae; there is no need for the separation of such individuals under the name Pseudochaetogaster longmeri. Amphichaeta leydigii and A. americana are recorded and Homochaeta raptisae is transferred to this genus. The source of the confusion between Vejdovskyella comata and V. intermedia is identified and both are now accepted as valid species and are recorded from Washington and British Columbia, respectively. Vejdovskyella hellei is transferred to Specaria. The distinction between Nais communis and N. variabilis is documented, and the serrate nature of the hair setae of N. elinguis is newly described. Pristina idrensis is new to the Canadian fauna; P. aequiseta is new to British Columbia and Washington. The few remaining differences between our records and those presented by other workers are catalogued, yielding a total of 65 confirmed species and two probable additions to the North American fauna.

Eight species of tardigrades in the family Echiniscidae were observed: Echiniscus horningi, Echiniscus mauccii, Echiniscus quadrispinosus, Echiniscus wendti, Hypechiniscus gladiator, Pseudechiniscus goedeni, Pseudechiniscus suillus, and Testechiniscus laterculus. Of these, six are new to British Columbia and three are new to Canada. Two species that were previously collected in 1908 and 1910 in British Columbia have been recollected. All eight species are described and illustrated.