RICE and STOKES: TOXICITY OF AMMONIA TO RAINBOW TROUT 



10 



20 



■ECC- 



30 



ao 50 



— ALEVINS- 



ACE IN DAYS 



60 



fry- 



Figure 1. — Twenty-four-hour median tolerance limits (TLm) of un-ionized ammonia to eggs 

 and alevins of rainbow trout ( 10°C, pH 8.3). Points indicate mean of two bioassays; bars indicate 

 the range. Adult trout 24-h TLm was 0.097 mg/liter (10°C, pH 8.3). 



brown trout, Salmo trutta, drops significantly 

 after 15 s in water — in our experiments this 

 was about the minimum time lapse between 

 stripping eggs into the water and introduction of 

 sperm. Because we did not control the time lapse 

 before sperm introduction precisely enough, we 

 cannot evaluate any subtle effects of ammonia 

 on prevention of fertilization. It was obvious, 

 however, that high ammonia concentrations did 

 not cause complete loss of eggs or sperm (Table 1) 

 because more than half of the eggs were ferti- 

 lized at all ammonia exposures. No obvious dif- 

 ferences in the percentages of eggs that hatched 

 were noticed between ammonia exposures of 

 2 or 3 min and 1 h, even at the highest concen- 

 trations of un-ionized ammonia (1.79 mg/liter) 

 we tested. The fertilization and water-hardening 

 stages are similar to later stages (before 50 days 

 of development) in their relative insensitivity 

 to ammonia when compared with older fry with 

 absorbed yolks (after about 60 days of develop- 

 ment). 



Our observations of great resistance of eggs 

 and alevins of rainbow trout to ammonia toxicity 

 are consistent with results of ammonia toxicity 

 studies of Penaz (1965) and with other studies 

 of other toxicants. Trout eggs and sac fry were 

 only slightly susceptible to endrin at concentra- 



tions that seriously affected adults (Wenger 1973). 

 Burdick et al. (1964) observed that a high pro- 

 portion of lake trout, Salvelinus namaycush, fry 

 from normal appearing eggs containing 2.95 ppm 

 DDT or more died. The sensitive fry died at the 

 completion of yolk absorption when feeding would 

 normally begin. Eggs of "common trout" were 

 less susceptible to anionic detergent toxicity 

 (sodium alkylsulphate) than alevins, whose sen- 

 sitivity continued to increase for 6 wk (Wurtz- 

 Arlet 1959). Eggs of two salmonids were about 

 one-tenth as sensitive to a commercial formula- 

 tion of rotenone and derivatives as fry at the 

 same temperature (Garrison 1968). A study of 

 zinc toxicity by Skidmore (1965) showed that eggs 

 of zebrafish, Brachydanio rerio, were relatively 

 less susceptible than newly hatched fish. 



It appears then that eggs and developing em- 

 bryos are resistant to several toxicants, including 

 ammonia. One obvious explanation for the resis- 



'Percentage hatch of each group of 250 eggs. 



209 



