RICE and BAILEY: SURVIVAL, SIZE, AND EMERGENCE OF PINK SALMON 



the incoming water line to each cup. Flow rates of 

 both water and ammonium sulfate were kept con- 

 stant by using supplies with a constant head. We 

 measured flow rates daily and concentrations of 

 total ammonia in each cup twice each week. 



In the long-term tests, three groups of alevins 

 (A, B, and C) were exposed to ammonium sulfate 

 solutions for three different lengths of time. Group 

 A was exposed for the 21 d preceding the comple- 

 tion of yolk absorption (time of normal emergence 

 and migration). Group B was exposed for 40 d, 

 with the exposure ending 21 d before yolk absorp- 

 tion. Group C was exposed for 61 d before yolk 

 absorption. In each group, subgroups of alevins 

 were exposed to concentrations of NH^ ranging 

 from (control) to 4 ppb. 



At the end of the long-term exposures when 

 control fry had absorbed all visible yolk, 50 fry 

 from each NH3 exposure were sampled and pre- 

 served in d^c Formalin. Size was determined after 

 6 wk when tissue hydration adjustments were sta- 

 ble. After blotting the fry with a damp paper towel, 

 fork lengths were measured to the nearest mil- 

 limeter and weights to the nearest milligram. 

 Mean Kjj developmental indices (Bams 1970) were 

 1.99 for the controls and 1.96-2.07 for the groups 

 exposed to NH3; therefore, fry were at similar de- 

 velopmental stages and the size of fry from the 

 various groups could be compared directly with 

 the size of controls. Data are reported as means 

 ±95% confidence intervals. 



In another experiment, the possible stimulation 

 of early emergence of immature fry was tested by 

 exposing alevins in gravel incubators to a single 

 exposure of NHg for 24 h at various times during 

 development. Concentrated ammonium sulfate 

 solutions were pumped into the intake lines of 

 small experimental gravel incubators (Rice and 

 Moles footnote 4) at rates sufficient to produce 

 desired concentrations of NH3. Alevins or fry were 

 trapped if they voluntarily emerged during the 

 exposure. The numbers of fry and stage of devel- 

 opment were noted daily. Pink salmon were judged 

 to have emerged early when they emerged before 

 control fry and were judged to have emerged pre- 

 maturely if yolk sacs were visible externally. Pipe 

 incubators with a volume of 5 1 and a water flow of 

 450 ml/min were seeded in November with 300 

 eyed eggs each. Each week after hatching, several 

 incubators were exposed to four different concen- 

 trations of NHg for 24 h. Each incubator received 

 only one 24-h treatment and different sets of in- 

 cubators were used for the NH3 exposures that 



were performed every week during the 2 mo prior 

 to emergence of controls. All NH3 concentrations 

 were measured analytically by the method previ- 

 ously described. 



SENSITIVITY OF DIFFERENT 

 LIFE STAGES TO AMMONIA 



Late alevins near emergence were the most sen- 

 sitive of all life stages tested to short-term, acute 

 concentrations of NH3 (Figure 1). Eyed eggs ex- 



T 1 r 



24JAN 14 FEB 13 MAR 



DATE OF ACUTE BIOASSAY 



10 APR 



Figure l.— 96-h median tolerance limits (TLm's) and ±95% 

 confidence limits of pink salmon alevins and fry exposed during 

 short-term, acute experiments to un-ionized ammonia (NH3). 

 Eggs were also tested, but no mortalities were observed at the 

 highest concentration (1,500 ppb NH^). 



posed for 96 h to toxicants in December were not 

 harmed by concentrations > 1,500 ppb and ap- 

 peared to hatch normally. Late alevins (tested 

 13-17 March) had the lowest 96-h TLm measured, 

 83 ppb of NH3. The fry (tested on 10-14 April) had 

 been feeding for 2 wk and appeared to have 

 slightly greater tolerance to NH3 than the alevins 

 tested just prior to emergence, but the differences 

 between the tests were not statistically signifi- 

 cant. Greater sensitivity just prior to emergence is 

 consistent with similar observations of trout eggs 

 and alevins exposed to ammonia (Penaz 1965; Rice 

 and Stokes 1975). Studies with other toxicants 

 have identified eggs to be much more tolerant than 

 alevins (Wurtz-Arlet 1959; Garrison 1968; Rice et 

 al. 1975). 



643 



