ACUTE TOXICITY OF AMMONIA TO SEVERAL DEVELOPMENTAL 

 STAGES OF RAINBOW TROUT, SALMO GAIRDNERI 



Stanley D. Rice' and Robert M. Stokes^ 



ABSTRACT 



Median tolerance limits derived from 24-h bioassays demonstrated that fertilized eggs and 

 alevins of rainbow trout, Salmo gairdneri, were not vulnerable to 3.58 ppm un-ionized ammonia 

 at 10°C (pH 8.3). At the end of yolk absorption, rainbow trout fry increased in susceptibility 

 dramatically; their median tolerance limit values were about 0.072 ppm, the same as for adult 

 trout. Fertilization of eggs was not prevented in un-ionized ammonia solutions up to 1.79 ppm, 

 the highest exposure tested. 



Much information is available on the toxicity of 

 ammonia to juvenile and adult trout, but the 

 paucity of information on the toxicity of ammonia 

 to fertilized eggs and larvae of teleosts is sur- 

 prising since these life stages are often assumed 

 to be relatively sensitive. Several studies have 

 examined ammonia toxicity to adult trout (Lloyd 

 1961; Ball 1967; Wilson et al. 1969), including 

 the effects of increased ammonia toxicity to trout 

 at lower oxygen levels (Downing and Merkens 

 1955) and decreased toxicity at higher carbon 

 dioxide levels (Lloyd and Herbert 1960). Tem- 

 perature, oxygen, pH, carbon dioxide, and bicar- 

 bonate alkalinity influence the toxicity of am- 

 monia and are discussed in a report by the 

 European Inland Fisheries Advisory Commission 

 (1970). Exposure of juvenile or adult salmonids 

 to ammonia has been associated with decreased 

 growth (Brockway 1950; Burrows 1964; Larmo- 

 yeux and Piper 1973), gill damage (Burrows 1964; 

 Reichenbach-Klinke 1967), and other sublethal 

 physiological effects (Reichenbach-Klinke 1967; 

 Fromm and Gillette 1968; Lloyd and Orr 1969), 

 and similar effects may occur with salmonid 

 eggs and alevins. Exposure to ammonia has also 

 been associated with increased incidence of 

 disease in juvenile and adult salmonids (Burrows 

 1964; Larmoyeux and Piper 1973) and in salmonid 

 alevins (Wolf 1957). 



The only study of toxicity of ammonia to eggs 

 and larvae (Penaz 1965) involved three stages 



'Department of Biological Science, Kent State University, 

 Kent, OH 44242; present address: Northwest Fisheries Center 

 Auke Bay Laboratory, National Marine Fisheries Service, 

 NOAA, P.O. Box 155, Auke Bay, AK 99821. 



^Department of Biological Science, Kent State University, 

 Kent, OH 44242. 



Manuscript accepted May 1974. 



FISHERY BULLETIN: VOL. 73, NO. 1, 1975. 



of eggs and two stages of yolk fry of Salmo 

 trutta. Penaz observed an increase in sensitivity 

 of the eggs with age to brief (120 min) exposures 

 to ammonia at pH 8 and temperatures of 5.68° 

 to 3.56°C. A similar pattern was observed with 

 longer exposures (10 h) of newly hatched and 

 12-day-old alevins to ammonia at pH 8 and 

 temperatures of 11° and 16.9°C. The early eggs 

 were resistant to the highest dose he tested — 

 50 mg/liter of un-ionized ammonia. These data 

 suggest changes in sensitivity with development, 

 but the changes in lengths of exposure and 

 temperature make it difficult to compare dif- 

 ferences between eggs and alevins. 



We used a series of bioassays to determine 

 the stage of development at which eggs and 

 larvae of rainbow trout, Salmo gairdneri, were 

 most susceptible to acute ammonia toxicity. Such 

 information is needed to establish realistic limits 

 for survival of eggs and larvae in both natural 

 and hatchery environments. Knowledge of con- 

 centrations of ammonia that may limit survival 

 is particularly important in hatchery operations 

 where it is advantageous to maintain the greatest 

 density of fish and eggs per unit water flow. 



MATERIALS AND METHODS 



Freshly fertilized rainbow trout eggs were 

 obtained from Bowden National Fish Hatchery, 

 W.V., (courtesy of the U.S. Bureau of Sport 

 Fisheries and Wildlife) and transported to the 

 laboratory within 6 h. 



About 2,000 of the eggs were poured under 

 water into 4-inch-square trays with nylon screen 

 bottoms at about 25 to 35 eggs per tray. For 

 incubation the trays were put into a 10°C water 



207 



