toxicant dispensing system designed by Mount and Warner (1965). This 

 system cycled e^jery 3 min to deliver 1 liter of water and a measured 

 amount of toxicant. Twelve levels of HCN were maintained from 5 to 100 

 ug/liter at pH 8.06-8.09, 24.8-25.1 °C and dissolved oxygen of 5.9-6.3 

 mg/liter. Cyanide concentrations were analyzed by the Epstein coloro- 

 metric method (APHA, 1971) from samples taken in the test chambers 3 

 times per week. HCN was calculated from dissociation constants of Izatt, 

 ct a£., (1962). Three controls with well water were run simultaneously 

 with the cyanide treatments. 



After 106 days minnows were transferred to 20 treatment and 5 control 

 chambers, each containing 35 liters of water and 20 fish. In 149 days or 

 when first spawning occurred, four mature males and three females were 

 selected and left in each treatment tank. 



After 192 days total exposure of fry and spawning adults, 50 eggs 

 from each treatment were placed in plastic cylinders with a screen on one 

 end. Cylinders were suspended in the same test water as adults and os- 

 cillated until the eggs hatched. After 22/ days from the start of expo- 

 sure of the parent generation, a growth and survival experiment was 

 started with second-generation fry. Length was determined photographi- 

 cally after 28 days of fry exposure, and length and weight were measured 

 directly at termination after 56 days. 



Ten 19-month-old adult brook trout were placed in 340 liter tanks 

 with eight cyanide treatments and two controls. Treatments ranged from 

 5.7-75.3 ug/liter HCN at 7.95 pH, 9.0-15 °C and 6.5-7.9 mg/liter 2 - The 

 HCN metering apparatus utilized was the same as for fathead minnows. 

 Temperature, pH and cyanide analyses were made 3 times per week. Exposure 

 began on May 5 and continued through spawning 196 days later. After 143 

 days, exposure spawning boxes were placed in the tanks and the number of 

 fish in each tank reduced to two males and four females. Spawned eggs 

 were removed from each box each day. 



From each spawning of 100 viable eggs, 50 were randomly selected and 

 placed in oscillating cups to hatch at 9 °C. Viability was determined at 

 12 days by development of the neural keel. Twenty-one days after hatch, 

 25 alevins (larvae) 15-19 mm long, depending on previous treatment, were 

 placed in 20-liter glass tanks where they were held at 9 °C. There were 

 3 replications in each of 8 treatments ranging from 5.6 to /7.5 yg/liter 

 HCN and 3 controls. Fish were measured photographically at the end of 

 each 30-day period, and at 90 days they were weighed. After 60 days, 

 fish numbers were reduced to 20. Alevins were fed an unrestricted diet 

 of dry trout food in pelletized form. 



RESULTS 



Fathead - First Generation 



After 28 days, survival in the first-generation experiment averaged 

 64 percent in the 3 controls and ranged from 80 to II percent in treat - 



41 



