FISHERY BULLETIN: VOL. 69, NO. 4 



We intended to compare hatchery-reared Chi- 

 nook salmon with wild or naturally migrating 

 spring Chinook salmon acclimated to the same 

 temperature. Wild fish were available only when 

 they were acclimated to temperatures near 10° C. 

 The hatchery population had deteriorated by 

 then, however, so we compared wild fish accli- 

 mated at 10° C and hatchery fish acclimated to 

 15° C (Figure 4). As expected, the hatchery 

 population — acclimated at the higher tempera- 

 ture — was able to tolerate the highest temper- 

 atures for a longer period, but when the LEso 

 curves — which include the effect of nitrogen — 

 are compared, little difference can be noted. This 

 indicates that results achieved in the laboratory 

 with hatchery stocks can be applied to wild Co- 

 lumbia River stocks with reasonable accuracy. 



SPRING CHINOOK (WILD) 

 10° C ACCLIMATION 



SPRING CHINOOK I HATCHER'T REARED) 

 I5°C ACCLIMATION 



PERCENTAGE SATURATION NITROGEN 



_l L I L. 



240 360 480 



TIME |minul«>) 



FlGllKE 4. — Comparison of le-,q curves between juvenile 

 wild and hatchery spring chinook salmon at various tem- 

 peratures and levels of saturation of nitrogen gas. 



EFFECT OF DEPTH ON RELATION 



BETWEEN SUPERSATURATION OF 



NITROGEN AND TOLERANCE OF 



JUVENILE FISH TO TEMPERATURE 



INCREASES 



Examination of fish in cages at the forebay of 

 Priest Rapids Dam (Ebel, 1969) indicated that 

 juvenile coho and chinook salmon would not con- 

 tract gas bubble disease if held at a sufficient 

 compensating depth (5 m). This finding sug- 

 gests that fish subjected to temperature in- 

 creases in addition to nitrogen supersaturation 

 would also be less affected if they remained at 

 sufficient depth when they encountered a tem- 

 perature increase. 



To test this hypothesis, we subjected coho 

 salmon acclimated at 10° C to three temper- 

 atures above acclimation in water supersatur- 

 ated at 130^f in the 9-m (deep) tank where they 

 could select any depth from the surface to 9 m ; 

 we then compared LEioo curves in the 20-cm 

 (shallow) tanks with those in the deep tank 

 (Figure .5). These curves definitely indicate 

 that the coho benefited by having the option to 

 sound in the deep tank. The LEioo level never 

 was reached during the 18-hr observation period 

 when the fish were subjected to 20° C (10° C 

 increase) in the deep tank, but occurred after 



, -t 23° C 



360 480 



TIME 



600 720 

 t mtnulti) 



Figure 5. — Comparison of lEiqq curves for coho salmon 

 acclimated at 10° C and subjected to three temperatures 

 (15°, 20°, and 23° C) in 20-cm and 9-m deep tanks 

 containing water supersaturated with nitrogen gas at 

 130'/' saturation. Oxygen concentrations varied from 

 115 to 125% saturation. 



840 



