A microassay well‐plate method is described for determining Na+,K+‐ATPase activities of small gill sections from juvenile Pacific salmon Oncorhynchus spp. The method differs from the established macromethod by detecting inorganic phosphate in nanomole rather than micromole concentrations. This permits the use of much smaller tissue samples, which makes it possible to release fish after sampling. Use of sonication during enzyme extraction and elimination of the need to deproteinize samples before ATPase analysis further simplify the assay. Application of the microwell‐plate technique for both Na+,K+‐ATPase activity and protein analysis permits rapid processing of many samples. It also produces results equivalent to those of the macroassay; no significant differences occurred between sample duplicates run by the two methods with the same enzyme extract (P > 0.05). The coefficient of variation (100·SD/mean) for microassay samples containing enzyme activities of at least 10 umol inorganic phosphate per milligram protein per hour was 12% or less for between‐plate comparisons and 5% or less for same‐plate comparisons. Monitoring of gill‐clipped fish during migration indicated that small gill clips did not cause mortality or alter migration behavior of juvenile salmonids tagged with passive integrated transponders. These are important considerations in programs for monitoring species listed under the U.S. Endangered Species Act.
The in situ depths of juvenile salmonids Oncorhynchus spp. were studied to determine whether hydrostatic compensation was sufficient to protect them from gas bubble disease (GBD) during exposure to total dissolved gas (TDG) supersaturation from a regional program of spill at dams meant to improve salmonid passage survival. Yearling Chinook salmon O. tshawytscha and juvenile steelhead O. mykiss implanted with pressure-sensing radio transmitters were monitored from boats while they were migrating between the tailrace of Ice Harbor Dam on the Snake River and the forebay of McNary Dam on the Columbia River during 1997-1999. The TDG generally decreased with distance from the tailrace of the dam and was within levels known to cause GBD signs and mortality in laboratory bioassays. Results of repeated-measures analysis of variance indicated that the mean depths of juvenile steelhead were similar throughout the study area, ranging from 2.0 m in the Snake River to 2.3 m near the McNary Dam forebay. The mean depths of yearling Chinook salmon generally increased with distance from Ice Harbor Dam, ranging from 1.5 m in the Snake River to 3.2 m near the forebay. Juvenile steelhead were deeper at night than during the day, and yearling Chinook salmon were deeper during the day than at night. The TDG level was a significant covariate in models of the migration depth and rates of each species, but no effect of fish size was detected. Hydrostatic compensation, along with short exposure times in the area of greatest TDG, reduced the effects of TDG exposure below those generally shown to elicit GBD signs or mortality. Based on these factors, our results indicate that the TDG limits of the regional spill program were safe for these juvenile salmonids.
1994. Assessing srnoltification of juvenile spring chinook salmon (Oncorhywchus tshawytscha) using changes i n body morphology. Can. J. Fish. Aquat. Sci. 51 : 836-844.A morphometrie measure of srnoltification of juvenile spring chinook salmon (Oncoshynchers tshawytscha) was developed and evaluated. Fish were collected from hatcheries i n Washington and Idaho prior to release and at McNary Darn on the Coieambia River during their downstream migration. Distances between 1 5 anatomical landmarks were digitized from photographs of each dish resulting i n 34 morphometric characters for analysis. The canonical variate calculated frsm a discriminant function based on several principal components was evaluated as a measure of srnoltification. The canonical variate was sigwificantly correlated with gill Naf-K' ATPase activity, a commonly used measure of smoltification. Measuring the morphometric characters and calculating the canonical variate is a relatively simple procedure and can be performed with little harm to the fish. This method of smoltification assessment may be ideally suited to studies in which sacrificing fish is not possible, such as those involving threatened or endangered species, or when access to a laboratory for sample analysis i s not available.O n a mis au point et 6valu6 une mesure morphologique de la smoltification de jeunes saumons quinnats (Oncorhynchus tshawytscha) du printemps. Bes sujets ont et6 preleves dans des bassin d'elevage des Etats de Washington et de I'ldaho avant Ieur remise en libertb, aiwsi qu'au barrage McNary du fleuve Columbia, dusant la devalaison. b'espace entre 15 traits anatomiques a kt6 nurnkris6 a partir de photographies de chaque sujet, ce qui a donne la possibilite d'analyser 34 caracteres morphologiques. La variable canonique calculee 21 partir d'une fowction discriminante etablie A partir de plusieurs composantes prim cipales, a et6 evaluee titre de rnesure de la smoltiiication. !I existe un rapport significatif entre cette variable et Il'activite de la ~a " -K " ATPase au niveau des branchies; il s'agit d'une mesure commune de la smoltification. La mesure des caractGres morphologiques et le calcul de la variable canonique constituent une methode relativement simple et qui cause peu de lesions aux poissons. Cette methode d'evaluation de la srnoltificatiogt se pr$te tout % fait aux etudes oh il est impossible de sacrifier des sujets, par exemple parce qu'il s'agit d'especes en danger ou en voie d'extinctisn, ou encore parce qu'il est impossible de proceder a des analyses des 6chantillons en laboratoire.
From 1988 through 1992, we assessed the prevalence (frequency of occurrence) and seventy (degree of infection) of Renibacterium salmoninarum (RS) among fish in marked groups of Columbia River basin and Snake River basin hatchery spring chinook salmon Oncorhynchus tshawytscha before release and during their seaward migration. During the study, prevalence of RS infection decreased (from >90% to <65%) in six of the eight hatchery groups. We attributed this decrease to changes in hatchery practices that reduced vertical and hori/.onlal transmission. Fish from Snake River hatcheries had a higher prevalence of infection when sampled at dams (mean >90%) than in the hatchery (mean <70%), but there were no differences in similar comparisons of Columbia River fish. Although prevalence and severity of RS infection were not correlated in the groups studied, it appears that fish from the Snake River were more severely infected than those from the Columbia River. Some groups of Snake River fish had higher severity of infection at dams than in the hatchery, but infection in fish from Columbia River hatcheries did not change. These differences between Snake River and Columbia River fish might have resulted from differences in river conditions and the distances from hatcheries to dams.Renibacterium salmoninarum (RS), which caus-
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