o 



DO 

 < 



r- 



t 5 



P 4 

 < 



CE 



I- 



UJ :> 

 o 



z 

 o 

 o 



UJ 



o 



>- 



X 



o 



Q 



O 

 CO 



co 



THEORETICAL CURVE FOR- 



CHUM SALMON (NEGATIVE 



CURVATURE) 



O" 





/ 



/ 



/ 



/ 



/ 



/ 



V f! 



/ 

 / • 



/ 





ii 



I 



U- 

 lo 



OBSERVED CURVE FOR 



ATLANTIC SALMON 

 (POSITIVE CURVATURE) 



100 200 300 400 500 600 



STAGE OF DEVELOPMENT 



(CENTIGRADE- DEGREE- DAYS) 



Figuhe 2. — Concentration of dissolved oxygen first 

 reducing rate of oxygen consumption by salmon embryos. 

 Upper curve is from Alderdice et al. (1958). Lower 

 curve is from Hays et al. (1951). Water temperature is 

 taken to be 10° C, and a centigrade-degree-day is 

 equivalent to a constant temperature of 1° C. above 0° 

 C. over a 24-hour period. 



In figure 2, the theoretical values of C at 10° C. 

 obtained for chum salmon by Alderdice etal. (1958) 

 (upper curve) are compared with limiting levels 

 determined experimentally for Atlantic salmon by 

 Hays et al. (1951). The most striking difference 

 between theoretical and observed limiting dis- 

 solved oxygen concentrations is the sign of curva- 

 ture of the connected points. It is doubtful if 

 difference in species would account for positive 

 curvature in Atlantic salmon and negative curva- 

 ture in chum salmon. The validity of equation (1) 

 as it applies to salmonid embryos is, therefore, 

 questioned. 



Wickett (1954) pointed out that the delivery rate 

 of oxygen to an egg or a larva is a function of water 

 velocity as well as oxygen content . Others (Coble, 

 1961 ; Shumway, 1960; Silver, 1960; Silver, Warren, 

 and Doudoroff, 1963) gave experimental evidence 



that variations in velocity affected embryonic 

 growth, development, and survival in much the same 

 manner as variations in oxygen content. 



According to curves of figure 2, embryos are most 

 susceptible to low dissolved oxygen levels near the 

 time of hatching. Evidence of this was presented 

 by Hays and Armstrong (1942) and Garside 

 (1959), who observed high mortality at hatching. 

 Because mortality increased with slight increases in 

 temperature, these authors attributed death to an 

 inadequate amount of dissolved oxygen diffusing 

 through the egg capsule. 



The effect of oxygen supply rate on growth, 

 development, and survival of salmonid embryos 

 has been investigated by several workers. The 

 dissolved oxygen level causing 50-percent mortality 

 of chum salmon embryos increased from about 

 0.4 mg./l. at fertilization to 1.4 mg./l. at hatching, 

 when apparent velocity * and temperature were 

 maintained at 85 cm. /hour and 10° C. (Alderdice 

 et al., 1958). Coho salmon eggs incubated at 

 near true velocity of 3 cm./hour, a temperature of 

 9° C, and an ox3 7 gen level of 2.4 mg./l. survived to 

 hatch but produced larvae about one-third the 

 volume of controls (Shumway, 1960). Similar 

 findings were reported by Silver, Warren, and 

 Doudoroff (1963), who experimented with chinook 

 salmon and rainbow trout, Salmo gairdneri, 

 embryos. At near true velocity of 6 cm./hour 

 and a dissolved oxygen content of 2.6 mg./l., 

 Silver (1960) observed abnormal development . 

 At similar low levels of dissolved oxygen, Alderdice 

 et al. (1958) and Garside (1959) described ab- 

 normal development of caudal regions during 

 somite formation. Garside also found that the 

 development rate was retarded significantly by 

 reduced oxygen level. 



Larvae are more tolerant of low dissolved 

 oxygen levels than are embryos. For Atlantic 

 salmon, Hays et al. (1951) found the dissolved 

 oxygen concentration limiting metabolism of 

 embryos to be 7.5 mg./l. at 10° C. After the 

 eggs hatched the limiting concentration decreased 

 to 4.5 mg./l. Initiation of active respiration 

 across gill membranes having vastly increased 

 respiratory areas may have caused the sudden 

 decrease in limiting oxygen concentration. 



1 Apparent velocity is measured by dividing the rate of flow by the cross- 

 sectional area ot the lied through which the water had passed. The actual 

 or true velocity is greater than the apparent velocity where part of the cross- 

 sectional area is occupied by eggs or other objects. 



4! is 



U.S. FISH AND WILDLIFE SERVICE 



