The oxygen consumptions of gill and kidney tissues of the cutthroat trout (Salmo clarki clarki) were determined by the direct method of Warburg. The respiration rates of tissues from fish ranging from 10 to 100 gm. were examined in relation to body weight. A decline in weight specific oxygen consumption for both tissues was observed. On a log-log plot, the regression coefficient for kidney was -.148 while that for gill was -.139. The decline did not support the .73 rule (Brody, 1945) at the level of tissue respiration. The oxygen consumptions of kidney and gill tissues were examined during a 168 hour period after transfer of the fish from fresh water to 65% standard sea water. A sharp initial rise in QO₂ of kidney tissue was noted during the first 48 hours after transfer, reaching a maximum at 20 hours. The kidney tissue respiration during the remainder of the experimental period remained significantly higher than the parallel control level. The gill tissue respiration declined rapidly during the first 10 hours after transfer and remained significantly below the control level during the whole experimental period. The results are discussed in relation to recent observations of Holmes, Chester Jones, Phillips, and Sexton, concerning possible hormonal regulation of salt-electrolyte and water metabolism by vasopressin and adrenocortical steroids in euryhaline species of salmonids. / Science, Faculty of / Zoology, Department of / Graduate

Microhabitat use by cutthroat trout and macrohabitat use by both cutthroat and rainbow trout were studied i n the Green River below Flaming Gorge Dam during the winters of 1988 and 1989. Microhabitat parameters used by cutthroat trout, such as focal velocity, depth, and fish elevation, differed significantly in eddies, runs, and riffles. Mean focal velocities in runs were 0.79 body lengths/seconds (bl/s), in riffles 0.66 bl/s, and in eddies 0.24 bl/s. Cutthroat trout size also varied significantly with macrohabitat; larger fish were found in riffles. Macrohabitat use by cutthroat trout and rainbow trout differed significantly among species, macrohabitat types, and months. Both rainbow trout and cutthroat trout macrohabitat use shifted from lower velocity habitats during winter to faster velocity habitats in summer. Cutthroat trout and rainbow trout used macrohabitats at seasonally differing rates. Riffles were never selected in proportion to their abundance, especially during high winter discharges. Cutthroat trout implanted with radiotransmitters exhibited little movement during diel monitoring and did not change their occupation of macrohabitats.

Nine hemoglobins have been isolated from the blood of cutthroat trout. All nine hemoglobins bind oxygen cooperatively and appear to be tetramers with molecular weights of -64,000. The oxygen equilibria and subunit structures of the purified hemoglobins were studied. In addition, the red blood cells of cutthroat trout were examined for the presence of ATP and GTP, which are known to be physiological modulators of hemoglobins in fishes. Five hemoglobins with isoelectric points from 9.1 to 7.0 are classified as cathodal hemoglobins. These five hemoglobins have identical oxygen binding properties by the criteria tested. All have oxygen equilibria which are unaffected by protons and ATP and essentially independent of temperature, with overall enthalpies of oxygenation ~0. Two hemoglobins with isoelectric points near 6.5, classified as a nodal hemoglobins, have oxygen binding properties distinctly different from those of the cathodal hemoglobins. Both are characterized by a Root effect, displaying non-cooperative oxygen binding and low oxygen affinity at pH 6.2. ATP causes a large reduction in the oxygen affinity without affecting the cooperativity of oxygen binding. GTP has a similar but slightly larger effect on both hemoglobins. The oxygen equilibria of the anodal hemoglobins are temperature dependent, with the oxygen affinity being reduced as temperature increases. The overall enthalpy of oxygenation is -14 kcal/mol for both hemoglobins. The two remaining hemoglobins represent only a small percentage of the total hemoglobin. These hemoglobins are tentatively designated as embryonic hemoglobins based primarily on a comparison of their properties to those observed for hemoglobins from newly-hatched rainbow trout (Iuchi, I. (1973) Comp. Biochem. Physiol. 44B, 1087-1101). These two hemoglobins have isoelectric points near 5.9 and oxygen binding properties similar to those of the cathodal hemoglobins. With the possible exception of one of the embryonic hemoglobins (for which globins were not obtained), all the hemoglobins are composed of two different types of globin chains. Six are ∝_2 β_2 tetramers, while two of the cathodal hemoglobins are hybrid tetramers of the type 〖∝∝'β〗_2 and ∝∝'ββ. Red blood cells of cutthroat trout contain both ATP and GTP, suggesting that, in contrast to rainbow trout, both nucleotides may be important physiological modulators of hemoglobin oxygen affinity in this fish.