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Fisheries Section Research Reports and Abstracts

Identification of Brown Trout Populations in Georgia

Project number: F-42
Study: II
Final Report Date:  August 1990
Period Covered: March - November 1988
Authors: Kimberly G. Norgren, Rex A. Dunham, R. Oneal Smitherman, Jeff Durniak, and Timmy B. Hess

Study Objectives
  1. To determine the relationship between isozyme markers and color phenotypes.
  2. To determine levels of genetic variability
  3. To evaluate the relationship between size and color morph
  4. To determine whether or not genetically distinct sympatric stocks exist for Georgia's populations of brown trout.

Brown trout were collected from four locations (Chattooga River, Jones Creek, Noontootla Creek and the Walhalla National Fish Hatchery). Three color phenotypes (original, crossbred and Walhalla) had been identified in these populations. The genetic relationship of these populations and phenotypes were assessed using isozyme analysis. Levels of genetic variability in these populations were lower than those previously reported for other brown trout populations in the United States. Among populations and among phenotypes, only subtle isozyme allele frequency differences existed, and all populations were closely related.  Chattooga River and original phenotype populations did not possess the GPI-2106 allele which was found at frequencies greater than 0.10 in other Georgia populations.  The LDH-5105 allele that was previously shown to be associated with large size in brown trout in Ireland was found in low frequency in samples from the Chattooga River and Jones Creek and was found in all phenotypes. Highest levels of LDH-5105 were found in Jones Creek. Generally, fish possessing the LDH-5105 allele were smaller rather than larger than average, though no fish ages were determined. No isozyme markers were found that were associated with a particular color morph. Size advantages or growth rate differences were not apparent for any color phenotype in the natural environment, but growth differences were emerging in the hatchery environment.

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