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A genetic basis for swim stamina differences between strains of the rainbow trout, Salmo gairdneri Winz, Robert Alan


Two wild strains of British Columbia rainbow trout (Salmo gairdneri) (Deadman Creek steelhead and Pennask Lake ) and 2 domesticated strains (Domestic-McLeary and Duncan River) were compared for evidence of genetic changes in swim stamina due to natural and artificial selection in hatcheries. The wild strains had approximately twice the swim stamina of the hatchery strains, with critical swim velocities (U[sub crit]) of 1.98 ± 0.08 (Pennask) and 1.91 ± 0.1 0 (Deadman) body lengths.sec⁻¹ vs. 1.36 ± 0.09 (Domestic) and 1.10 ± 0.06 (Duncan) body lengths.sec⁻¹. These two categories of strains also differed in certain genetic/biochemical and morphological characteristics which have been linked to swimming ability. The results of this study reveal that: (1) In the exercised state, the Pennask and Deadman strains convert lactate to pyruvate in the liver at the following maximum rates: 151.92 ± 5.25 and 150.64 ± 5.74 I.U.g⁻¹ wet weight, while the Domestic and Duncan convert at slower rates: 86.48 ± 1.78 and 109.20 ± 3.11 I.U.g⁻¹. Lactate oxidation in whole blood shows a similar trend. (2) No correlation was found between swim stamina and LDH B² genotype. However the two high stamina "wild" strains were the only heterozygous groups. (3) Lactate levels in the brain showed no change with exercise in the "wild" strains, while a 2.5 fold increase was observed for the "hatchery" strains. (4) Hemoglobin concentration during exercise was higher for the Pennask and Deadman strains, 1.73 ± 0.04 and 1.75 ± 0.05 mM, vs. 1.61 ± 0.03 and 1.54 ± 0.03 mM for the Domestic and Duncan strains. (5) The percentage of non-Bohr/Root hemoglobin was approximately 30% for all 4 strains. (6) The Duncan strain was the only one to show a nucleoside triphosphate/hemoglobin (NTP/Hb) ratio of less than unity during exercise (0.89 ± 0.04). (7) This strain is also monomorphic for the rare LDH B²” allele. (8) The Deadman and Duncan strains had greater percentages of GTP in their erythrocytic NTP pools in both the exercised and baseline states. Poor survival after release into the wild is a negative characteristic of domesticated stocks of hatchery trout. A major component of the ability to survive in the wild is swim stamina. Domestication selection (a form of natural selection) in hatcheries against unnecessary swimming capacity is a potential reason why trout raised from hatchery brood stocks perform so poorly. High swim stamina is not as necessary for survival in the hatchery environment as it is in a trout's natural environment. Also, additional artificial selection for rapid growth characteristics may be mutually exclusive with any type of selection for high swim stamina.

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