and physical factors. It is reduced by oxidation 

 of organic detritus and respiration of or- 

 ganisms, and replenished (prinnarily) by 

 stream water entering the streambed. Inter- 

 change between stream and intragravel water 

 is affected by streamflow, gradient, curvature 

 of the streambed, and coarseness and permea- 

 bility of bed materials (Vaux, 1968). 



The supply of dissolved oxygen in a spawning 

 bed is continually renewed by the flowing 

 stream water. If the velocity of the flowing 

 water is reduced because the hydraulic gradient 

 or the permeability of the streambed is low, 

 the amount of dissolved oxygen may not be 

 sufficient to maintain optimum growth and de- 

 velopment of embryos and alevins or the 

 waste products of metabolism may accumulate. 

 Low velocity also increases the time that water 

 is exposed to the biochemical oxygen demand 

 of the streambed, causing a further reduction 

 in the availability of dissolved oxygen to eggs 

 and alevins and a further buildup of waste meta- 

 bolites, especially in summer when the water 

 is warm. Wickett (1958) and McNeil (1 966b and 

 1968) reported high mortality in salmon eggs 

 and alevins that had been deprived of dissolved 

 oxygen because of low permeability of bed 

 materials and limited interchange between 

 stream and intragravel water. Coble (1961) and 

 Phillips and Campbell (1962) showed that low 

 dissolved oxygen in intragravel water (as a 

 result of low velocity) retarded growth and 

 limited survival of coho saln-ion, O^. kisutch , 

 and rainbow trout, Salmo gairdnerii . Low 

 dissolved oxygenlevels induced experimentally 

 also caused substantial reduction in the size 

 of newly hatched alevins and a high percentage 

 of abnormalities: Shumway, Warren, and 



Doudoroff (1964) reared embryos of coho salm- 

 on at a water velocity of 3 cm./hr, and an 

 oxygen level of 2.4 mg./l.; the alevins at 

 hatching were only one-third the size of con- 

 trol samples. Silver, Warren, and Doudoroff 

 (1963) had similar results in a study of chinook 

 salmon, O^ tshawytscha , and rainbow trout. 



Although low levels of dissolved oxygen re- 

 tard development up to hatching, the rate of 

 growth of the alevin appears to compensate 

 partly for such retarded growth, provided 

 adequate oxygen and waterflow are available. 

 Hamdorf (1961) found that rainbow trout em- 

 bryos exposed to hypoxial conditions were 

 much smaller at hatching than a control group. 

 He found, however, that if he reared the alevins 

 of these sanne embryos in water saturated with 

 dissolved oxygen, they soon approached the size 

 of the fry from the control group. Brannon 

 (1965) reported similar results from eggs of 

 sockeye salmon, O. nerka , that had been reared 

 under hypoxial conditions; the alevins produced 

 fronn such eggs were one-half the weight of 

 those reared at oxygen saturation. Brannon ob- 

 served little difference in body weight at yolk 

 absorption for the embryos, but for the fry 

 reared under hypoxial conditions, yolk absorp- 



tion was delayed about 3 weeks. Neither 

 Hamdorf nor Brannon measured anatomical 

 features such as eye diameter or length of 

 pectoral fin. The possibility that such measure- 

 ments may be better indicators of environ- 

 mental stresses in early development than 

 measurements of body length or weight is sup- 

 ported by the present study. 



ACKNOWLEDGMENTS 



The research reported here was started 

 while the authors were BCF employees at 

 Little Port Walter, Alaska. Several BCF staff 

 members assisted with the sampling programs. 

 Microscopic examination of the samples was 

 done at the Zoology Department, University 

 of Denver, Colo. 



LITERATURE CITED 



BRANNON, E. L. 



1965. The influence of physical factors on 

 the development and weight of sockeye 

 salmon embryos and alevins. Int. Pac. 

 Salmon Fish Comm., Progr. Rep. 12, 

 26 pp. 



COBLE, DANIEL W. 



1961. Influence of water exchange and dis- 

 solved oxygen in redds on survival of 

 steelhead trout embryos. Trans. Amer. 

 Fish. Soc. 90: 469-474. 



HAMDORF, K. 



1961. Die Beeinflussung der Embryonal und 

 Larvalentwicklung der Regenbogen- 

 forelle ( Salmo irideus Bigg.) durch die 

 Umweltfactoren Oj-- Partialdruck und 

 Temperatur. Z. Vergl. Physiol. 44: 523- 

 549. 



McNEIL, WILLIAM J. 



1964. A nnethod of measuring mortality of 

 pink salmon eggs and larvae. U.S. Fish 

 Wildl. Serv., Fish. Bull. 63: 575-588. 



1966a. Distribution of spawning pink salmon 

 in Sashin Creek, southeastern Alaska, 

 and survival of their progeny. U.S. Fish 

 Wildl. Serv., Spec. Sci. Rep. Fish. 538, 

 iv H 12 pp. 



1966b. Effect of the spawning bed environ- 

 ment on reproduction of pink and chum 

 salmon. U.S. Fish Wildl. Serv., Fish. 

 Bull. 65: 495-523. 



1968. Migration and distribution of pink 

 salmon spawners in Sashin Creek in 

 1965, and survival of their progeny. 

 U.S. Fish Wildl. Serv., Fish. Bull. 

 66: 575-586. 

 PHILLIPS, ROBERT W., and HOMER J. 

 CAMPBELL. 



1962. The embryonic survival of coho 

 salmon and steelhead trout as influenced 

 by some environnnental conditions in 

 gravel beds. Pac. Mar. Fish. Comm., 

 14th Annu. Rep. 1961: 60-73. 



