ficantly affected at HCN levels of 43.5 yg/liter and lower. At concentra- 

 tions of 55.3 to 77.2 yg/liter survival was significantly less than con- 

 trols (p^O.05). At 77.2 yg/liter survival from hatch was 30.0 percent 

 compared to 98.6-100 percent in controls. 



Growth of Brook Trout Alevins-- 



Length and weight of alevins at hatch was not significantly different 

 at the various HCN concentrations, but growth over a 90-day period was 

 markedly affected by increased HCN concentrations (Table 7). The effect 

 on growth was noted after 30 days and was great at 90 days. Fish at all 

 treatment levels from 33.3 to 77.2 yg/liter were significantly shorter 

 and lighter than controls (Figure 3). At 90 days length varied from 

 41.9 mm in controls to 24.3 mm at 77.2 yg/liter. Weight varied from 

 1.03 g in controls to 0.16 g at 77.2 yg/liter. At the highest concentra- 

 tion weight was 15.7 percent of controls. At 11.3 yg/liter growth after 

 90 days was significantly greater than the control, but at 5.6 and 

 21.8 yg/liter no significant difference from controls was noted. All 

 fish at treatment levels from 33.3 to 77.2 yg/liter at 90 days were 

 significantly slower in growth than controls. 



10 



20 30 40 50 60 

 HCN CONCENTRATION, jug/I 



70 



Figure 3. Growth of brook trout in various concentrations of HCN, 

 Expressed as percentage of controls. 



50 



