Effects of Prolonged Exposure to Ammonia on Fertilized Eggs and Sac Fry of Rainbow Trout (Salmo gairdneri)

Effects of ammonia on fertilized eggs and resulting sac fry of rainbow trout (Salmo gairdneri) were tested at concentrations of un-ionized ammonia ranging from 0.05 to 0.37 mg/liter (as NH3 - N). Exposure was continuous throughout the incubation period and for 42 days thereafter. There was no differential egg mortality or effect on incubation period. The lowest concentration of 0.05 mg/liter NH3 - N caused some retardation of early growth and development and 0.1 mg/liter caused similar but more severe effects throughout most of the test period. Hypertrophy of secondary gill lamellae epithelium occurred at 0.19 mg/liter. Karyolysis and karyorrhexis occurred in the same tissue at 0.28 mg/liter. Pale coloration and blue-sac disease occurred in sac fry at concentrations of 0.19 mg/liter and higher. The estimated incipient LC50 (lethal threshold concentration) for rainbow trout sac fry was 0.25 mg/liter NH3 - N.