SURVIVAL, SIZE, AND EMERGENCE OF PINK SALMON, 



ONCORHYNCHUS GORBUSCHA, ALEVINS AFTER 

 SHORT- AND LONG-TERM EXPOSURES TO AMMONIA 



Stanley D. Rice and Jack E. Bailey^ 



ABSTRACT 



Eggs and alevins of pink salmon, Oncorhynchus gorbuscha , were exposed to ammonia in a series of stat- 

 ic and flow-through experiments to determine what levels of ammonia would decrease survival. Short- 

 term acute toxicity tests (96 hours) were conducted at several stages in development to determine 

 which of the early life stages were most sensitive to ammonia. Long-term tests (up to 61 days! with 

 lower ammonia concentrations were conducted to determine effects on survival and size of fry at emer- 

 gence. The possibility of ammonia stimulating emergence of immature fry was tested at various stages 

 of development. 



Pink salmon alevins were most sensitive at the completion of yolk absorption, when the 96-hour 

 median tolerance limit was 83 parts per billion of un-ionized ammonia. Concentrations as low as 1.2 

 parts per billion reduced fry length in the 61-day exposures. Only levels above 10 parts per billion of 

 ammonia stimulated early emergence of immature fry. 



The concentrations of ammonia causing any of the deleterious effects observed are greater than con- 

 centrations observed in the hatcherv or the natural environment. 



Ammonia is a natural waste product of protein 

 catabolism and can be toxic to aquatic organisms 

 under certain conditions. Ammonia exists in the 

 water in two forms, un-ionized NHg and ionized 

 NH^^; the NHg is much more toxic than NH4^ 

 (European Inland Fisheries Advisory Commission 

 1970). The percentage of ammonia in the more 

 toxic form, NHg, is influenced primarily by pH of 

 the water and by factors that influence pH, e.g., 

 temperature, carbon dioxide, and bicarbonate al- 

 kalinity (European Inland Fisheries Advisory 

 Commission 1970). 



Much information is available on the toxicity of 

 ammonia to fishes, including juvenile and adult 

 salmonids; but it is surprising that little informa- 

 tion exists on the toxicity of ammonia to fertilized 

 eggs and larvae of teleosts, especially because 

 these life stages are often assumed to be relatively 

 sensitive. In acute toxicity studies, trout eggs and 

 alevins^ are much more tolerant to ammonia than 

 fry ( Penaz 1965; Rice and Stokes 1975). Long-term 



'Northwest and Alaska Fisheries Center Auke Bay Labora- 

 tory, National Marine Fisheries Service, NOAA, PO. Box 155, 

 Auke Bay AK 99821. 



^After hatching, alevins (salmon larvae) reside in the spawn- 

 ing gravels for several months while consuming their large 

 yolks. Salmon alevins that have no externally visible yolk ("but- 

 toned up") become fry when they inflate their swim bladder and 

 become free-swdmming; this occurs immediately after volitional 

 emergence from natural redds and gravel incubators. 



Manuscript accepted January 1980. 

 FISHERY BULLETI.N: VOL 78. NO. 3, 1980. 



studies of larval and juvenile forms exposed to 

 ammonia are virtually nonexistent; but in one 

 long-term study Burkhalter and Kaya (1977) con- 

 tinuously exposed rainbow trout, Salmo 

 gairdneri, eggs and alevins to ammonia until the 

 end of yolk absorption (about 67 d). They found 

 retardation of growth at the lowest concentrations 

 tested and other adverse effects at higher concen- 

 trations. 



Toxicity of NHg to the early life stages of salmon 

 in the northern latitudes would not be a problem 

 because low temperature and pH cause most of the 

 ammonia (99-1-%) in the water to be in the less 

 toxic form, NH^*. However, salmon eggs and ale- 

 vins in subarctic latitudes have a long devel- 

 opmental life history in an intragravel stream en- 

 vironment (up to 8 mo) where intragravel 

 waterflow can be reduced for several months dur- 

 ing the winter because of low temperatures. The 

 low waterflow may not be sufficient to prevent a 

 buildup of excreted ammonia in the water layer 

 immediately adjacent to the developing egg or ale- 

 vin. Ammonia levels may rise during these periods 

 of low flow to concentrations that are deleterious 

 to survival, health, and/or growth of the develop- 

 ing salmon. 



Our study had three specific objectives: 1) to 

 determine the sensitivities (judged by survival) of 

 early life stages of pink salmon, Oncorhynchus 



641 



