population we established a daily ration for test 

 groups of four dead smelt and one live steelhead 

 fingerling. One-half of the smelt introduced as 

 food were cut in half to accommodate the smaller 

 squawfish. 



RESULTS AND DISCUSSION 



Laboratory Bioassay 



Substantial squawfish mortality occurred in 

 tests at 126, 120 and 117% saturation. One hundred 

 percent mortality occurred in 20 hours at the 126% 

 level; 60% loss occurred within the 12-day test period 

 at the 120% level; and 32% at 117% saturation. 

 Mortality from gas bubble disease did not occur at 

 110, 107 or 100% T.D.G. saturation. Lethal exposure 

 times for 10 and 50% mortality (LE 10 and LE 50 ) for 

 squawfish are compared in Table 2 with LEio and 

 LE 50 values established (Dawley and Ebel, 1974 and 

 Dawley et al., 1975) for potential salmonid prey. It 

 is evident that squawfish are somewhat more toler- 

 ant than juvenile steelhead and spring chinook, 

 but have much less resistance than fall chinook fry. 



Gas bubble disease signs were found in all fish 

 exposed to 126, 120 and 117% T.D.G. saturations. 

 Eighty-nine percent of the squawfish exposed to 

 110% saturation also had gross signs of gas bubble 

 disease; one of ten fish exposed to 107% T.D.G. satu- 

 ration exhibited signs. No signs were noted at 100% 

 T.D.G. saturation (Fig. 2). Gross gas bubble disease 

 signs included hemorrhage and subcutaneous 

 blisters present over large areas of their bodies. All 

 fish showing signs of gas bubble disease exhibited 

 grossly distended blisters between the fin rays. 

 Exophthalmia ("pop-eye") occurred in only two 

 experimental fish. Gaseous emboli were noted in 

 the blood vessels of at least one gill arch in all gas 

 bubble disease mortalities. Emboli were also ob- 

 served in the gills of all squawfish surviving the 



110 120 



PERCENT SATURATION (T.D.G.) 



FIG. 2 Gas bubble disease symptoms in northern squawfish 

 with increasing T.D.G. saturation. 



120% saturation test and many surviving the 117% 

 T.D.G. tests. Gill emboli were not detected in squaw- 

 fish exposed to lower saturation. 



Active feeding decreased from an average of 

 14.3 g food per fish per day for squawfish exposed 

 to 100% saturation down to 2.3 g food per fish per 

 day for squawfish exposed to 120% T.D.G. satura- 

 tion (Fig. 3). These data indicate that feeding would 

 be reduced by 50% at about 115% saturation. Below 

 test saturations of 120%, squawfish showed a pref- 

 erence for live steelhead over the dead smelt (Fig. 4). 

 The number of test days the ration of live steelhead 

 was consumed was reduced about 40% when test 

 fish were exposed to 117% T.D.G. saturation. Squaw- 



TABLE 2 A Comparison of Lethal Exposure Times for Squawfish and Potential Salmonid Prey 

 with 2.5% Hydrostatic Compensation 



Effects on Squawfish 43 



