Natural Hybridization between Steelhead Trout (Salmo gairdneri) and Coastal Cutthroat Trout (Salmo clarki clarki) in Two Puget Sound Streams

1985 ◽  
Vol 42 (1) ◽  
pp. 110-119 ◽  
Author(s):  
Donald E. Campton ◽  
Fred M. Utter
Keyword(s):  
Management Practices ◽  
Random Mating ◽  
Puget Sound ◽  
Cutthroat Trout ◽  
Natural Hybridization ◽  
Salmo Gairdneri ◽  
Hybrid Index ◽  
Steelhead Trout ◽  
Mixed Ancestry ◽  
Coastal Cutthroat Trout

A genetic investigation of anadromous trout populations in the Puget Sound area revealed numerous juvenile individuals from two streams with electrophoretic phenotypes consistent with those expected for hybrid descendents of steelhead trout (Salmo gairdneri) and coastal cutthroat trout (S. clarki clarki). The likelihood of hybridization was evaluated with a hybrid index measuring the relative probability that the combined genotype for a particular fish at several diagnostic loci could have arisen by random mating within each of the two Salmo species. The distribution of hybrid index scores among fish from the two creeks clearly demonstrated the genetic distinctness of the two species and the intermediate genotypic composition of the unknown fish. We concluded that these electrophoretically intermediate fish were natural steelhead–cutthroat hybrids based on their restricted occurrence at specific sample sites in only 2 of 23 streams surveyed, the linear distributions of juveniles from the two parental species within each stream, and the distribution of hybrid index values for a hatchery population of known mixed ancestry. Further, from estimates of gametic disequilibria and the absence of a consistent excess of heterozygotes we suggest that backcrossing may have occurred. The existence of these natural hybrids raises many questions concerning the biological bases for maintaining species integrities in regions of sympatry and indicates the need to fully understand the biological consequences of present and future management practices.

The Relation between Scale Diameter and Body Length of Kamloops Trout, Salmo gairdneri kamloops

1955 ◽  
Vol 12 (5) ◽  
pp. 742-753 ◽  
Author(s):  
S. B. Smith
Keyword(s):  
Fork Length ◽  
Cutthroat Trout ◽  
Salmo Gairdneri ◽  
Steelhead Trout ◽  
Double Logarithmic Plot ◽  
Relative Growth ◽  
Coastal Cutthroat Trout ◽  
Constant Slope ◽  
Salmo Clarki ◽  
Simple Proportion

The scale/body relationship for Kamloops trout is very close to direct proportion for fish larger than 4.5 cm. fork length. The resultant plot on a double logarithmic grid is linear with a slope not significantly different from 1.00 (45°). Calculations of lengths of trout from scales at ages previous to that of capture can be made on the basis of simple proportion in two ways, (1) by use of a constant slope (45°) on a double logarithmic plot, or (2) by use of a constant zero-zero intercept on an arithmetic plot.Growth of the scales of the young is characterized by relatively rapid increase from time of scale formation, 3.5 cm. fork length up to 4.5 cm. At about 4.5 cm. fork length there is a sharp break (inflection) in the relative growth curve toward isometric growth of scales and body. Reliable estimates of the length of trout may be obtained from scales alone, using the diameter of the first circulus of the scale, the slopes and inflection of the relative scale/body plot and total diameter of the scale at time of capture.Marked Kamloops trout of known size were released in 1953. Subsequent recaptures both in 1953 and 1954 substantiated the accuracy of the method of estimating lengths of trout at ages previous to that of capture.Observations on the steelhead trout, Salmo gairdneri gairdneri, and on the coastal cutthroat trout, Salmo clarki clarki, suggest that an isometric scale/body relationship may exist among those species also.

Scale Characteristics of Yearling Coastal Cutthroat and Steelhead Trout

1957 ◽  
Vol 14 (2) ◽  
pp. 203-212 ◽  
Author(s):  
E. H. Vernon ◽  
R. G. McMynn
Keyword(s):  
Fork Length ◽  
Cutthroat Trout ◽  
Salmo Gairdneri ◽  
Steelhead Trout ◽  
Scale Growth ◽  
Scale Size ◽  
Species Overlap ◽  
Coastal Cutthroat Trout ◽  
Scale Characteristics ◽  
Salmo Clarki

Some scale characteristics of 88 yearling coastal cutthroat trout (Salmo clarki clarki) and 96 yearling steelhead (Salmo gairdneri) were compared in some detail. Although the number of diagonal scale rows above the lateral line was significantly higher in cutthroat, the counts of the two species overlap. The correlation of scale circuli counts with scale diameter was 0.94 for steelhead and 0.90 for cutthroat. At any given scale size cutthroat had 8 per cent more circuli than steelhead scales. Measurements of lateral and longitudinal diameters and anterior radii of scales show that the anterior portions of cutthroat scales tend to be longer and narrower than those of steelhead.Regression analyses of each scale measurement on fork length indicated that, for any given fork length, cutthroat scales are smaller than those of steelhead; the greatest difference being apparent when anterior radii are compared. Growth of scales in a dorsoventral plane approximates isauxesis in relation to fork length but scale growth in a longitudinal plane tends toward positive heterauxesis which is particularly pronounced in the anterior portions of scales.Multiple regression analyses of scale diameter, scale row count and fork length indicated that the smaller size of cutthroat scales is not balanced by proportionate increase in their number. When scale diameter is adjusted for scale number and fork length, cutthroat scales are 15.6 per cent smaller than those of steelhead, indicating that young cutthroat are covered by their scales with less overlap.

Ceratomyxa shasta Noble, 1950 (Myxozoa: Myxosporea) present in the Fraser River system of British Columbia

1983 ◽  
Vol 61 (9) ◽  
pp. 1991-1994 ◽  
Author(s):  
T. E. McDonald
Keyword(s):  
British Columbia ◽  
Chinook Salmon ◽  
Oncorhynchus Tshawytscha ◽  
Drainage Basin ◽  
Coho Salmon ◽  
Cutthroat Trout ◽  
River System ◽  
Salmo Gairdneri ◽  
Fraser River ◽  
Steelhead Trout

An examination of 220 chinook salmon (Oncorhynchus tshawytscha), 84 coho salmon (O. kisutch), 145 steelhead trout (Salmo gairdneri), and 21 cutthroat trout (S. clarki) for Ceratomyxa shasta (Myxozoa: Myxosporea) from 16 localities in the Fraser River drainage, British Columbia, showed that at all sites examined these salmonid species were infected, with a prevalence ranging between 11 and 100%. The study concludes that C. shasta, the causative agent of the salmonid disease ceratomyxosis, is widely distributed in the Fraser drainage basin and discusses these results in relation to proposed fish culture in the region.

Genetic Structure of Anadromous Cutthroat Trout (Salmo clarki clarki) Populations in the Puget Sound Area: Evidence for Restricted Gene Flow

1987 ◽  
Vol 44 (3) ◽  
pp. 573-582 ◽  
Author(s):  
Donald E. Campton ◽  
Fred M. Utter
Keyword(s):  
Gene Flow ◽  
Gene Diversity ◽  
Genetic Relationships ◽  
Puget Sound ◽  
Cutthroat Trout ◽  
Restricted Gene Flow ◽  
Pleistocene Glaciation ◽  
Expected Heterozygosity ◽  
Coastal Cutthroat Trout ◽  
Salmo Clarki

Genetic relationships among anadromous populations of coastal cutthroat trout (Salmo clarki clarki) in the Puget Sound area (United States) were investigated by electrophoretic methods between successive year classes within streams (populations), among streams within drainages, between drainages within each of two regions separated by Puget Sound, and between the two regions. Average allele frequencies for fish from the two regions differed by approximately 0.10 at several polymorphic loci, suggesting that gene flow between the two regions is restricted. Despite this divergence, the sampled populations were all very similar genetically (Nei's I > 0.97), possibly reflecting a common ancestral invasion following Pleistocene glaciation. The total gene diversity (expected heterozygosity) was 0.101 and was partitioned as follows: between regions, 1.24%; between drainages, 1.01%; among streams, 2.41%; between year classes, 1.17%; within individual year class samples, 94.2%. In addition, stream effects were significant in 7 of 12 intralocus ANOVA comparisons, suggesting that populations were structured genetically at this level of subdivision. This latter result may be reflecting the homing instinct of spawning adults.

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