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The multiple hemoglobins of coho salmon : Oncorhynchus kisutch Giles, Michael Arthur

Abstract

Studies were conducted to determine the onto genetic changes in the number and relative concentration of the electrophoretically distinguishable hemoglobin polymorphs of coho salmon, Oncorhynchus kisutoh and the influence of certain environmental factors upon the expression of the hemoglobin variants. In addition some of the oxygen equilibrium characteristics of the hemoglobin of freshwater fry and adult coho were investigated using both hemolyzates and whole blood. Throughout the life cycle of coho salmon seventeen to nineteen distinct hemoglobin components were identified in micro-starch-gel electropherograms prepared in borate buffer at pH 8.5. These components formed three main electrophoretic hemoglobin patterns associated with different stages of the life cycle. Unhatched embryos and alevins possessed twelve anodic and one cathodic components. All except three anodic components had disappeared from the blood of free-swimming fry fourteen weeks after hatching. This three-component pattern was retained until the beginning of the presmolt period, approximately eleven months after hatching. At this stage, five new cathodic components, one new anodic component and one anodic component which had previously been visible in alevin electropherograms appeared. In presmolts and smolts these additional seven components accounted for less than 20 % of the total hemoglobin of the blood while the three components observed in fry blood accounted for the remainder. Following migration to sea water the relative concentration of these seven components gradually increased to 45 to 50% of the hemoglobin over a two-month period. No further change in either the number or relative concentrations of the hemoglobin components was observed during the remaining phases of the life cycle. Since it was apparent that changes in hemoglobin pattern were temporally associated with changes in the characteristics of the environment occupied by the juvenile coho the effects of water temperature, dissolved oxygen concentration and salinity upon the physical development and electro-phoretic hemoglobin pattern of underyearling coho were examined. Exposure to freshwater temperatures of 1.4 to 15.0 C, dissolved oxygen concentrations of 2.2 to 9.7 ppm and salinities of 0 to 30 °/oo for periods of 49 to 60 days had no influence upon the electrophoretic hemoglobin pattern of either 3 1/2-month-old fry or 11-month-old presmolts. Presmolts reared for 60 days in freshwater at 15 C and in 10 °/oo salinity at 9.2 C grew at a highly accelerated rate and were equal or greater in size than 16 1/2-month-old postsmolts which had been residing in sea water for one month. These large presmolts retained the hemoglobin pattern characteristic of normal presmolts of the same age. Postsmolts maintained in aerated freshwater rather than sea water underwent changes in the electrophoretic hemoglobin pattern characteristic of sea-water residents. The foregoing observations suggest that age rather than physical size or environmental factors is the main determinant in the expression of the polymorphic hemoglobins of coho salmon. The oxygen equilibrium characteristics of adult coho hemoglobin and hemoglobin components A6-8 (fry hemoglobin) isolated from adult hemolyzates by ion-exchange chromatography were investigated. Adenosine triphosphate concentrations ranging from 0.0 to 0.76 moles/mole hemoglobin had no influence upon the oxygen equilibrium of adult hemolyzates whereas at a concentration of 7.56 moles/mole P₅₀ increased by 1 to 2 mm Hg. Since erythrocyte ATP concentrations of freshwater adult coho ranged between 0.8 and 1.3 moles/mole hemoglobin this organic phosphate is probably not a modifier of oxygen affinity in coho salmon. The hemoglobin of adult coho was relatively insensitive to variations in pH and temperature with ∅ =-0.172 at 9.8 C over the pH range of 6.95 to 8.20 and Δ log P₅₀ = 0.019 between 5 and 15 C. The Bohr effect of fry hemoglobin was nonlinear so that ∅ = -0.033, -1.729 and -0.182 in the pH ranges of 6.82 to 7.08, 7.08 to 7.50 and 7.50 to 8.50, respectively. The estimate of Δ log P₅₀ was 0.056 for fry hemoglobin. Thus at 9.8 C the oxygen affinity of fry hemoglobin exceeded that of adult hemoglobin at pH greater than 7.3 but was lower at values of pH less than 7.3. At pH 7.4, the P₅₀ of fry and adult coho hemoglobin was 8.4 and 17.9, respectively. In neither case was a Root effect observed. Heme-heme interaction was similar for both adult and fry hemoglobin and the value of n always exceeded 1.0. The estimate of n was generally less than 2.0 at pH greater than 7.0 and tended to decrease as the pH or the equilibration temperature increased. Studies with fry and adult whole blood equilibrated With 0.2 and 3.4 mm Hg of carbon dioxide generally confirmed the qualitative differences observed between the oxygen equilibria of fry and adult hemolyzates. The estimates of P₅₀ at 9.3 C and PCO₂ of 0.2 and 3.4 mm Hg were 5.5 and 12.5 mm Hg respectively for fry blood and 10.7 and 15.6 mm Hg, respectively, for the blood of freshwater adults.

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