Increased Toxicity of Ammonia to Rainbow Trout (Salmo gairdneri) Resulting from Reduced Concentrations of Dissolved Oxygen

Abstract

The median lethal concentration (LC50) of aqueous ammonia at reduced dissolved oxygen (D.O.) concentrations was tested in acute toxicity tests with rainbow trout (Salmo gairdneri) fingerlings. Fifteen 96-h flow-through tests were conducted over the D.O. range 2.6–8.6 mg/L, the former concentration being the lowest at which control fish survived. There was a positive linear correlation between LC50 (milligrams per litre un-ionized ammonia) and D.O. over the entire D.O. range tested; ammonia toxicity increased as D.O. decreased. Ammonia LC50 values were also computed for 12, 24, 48, and 72 h; the correlation with D.O. was greater the shorter the time period.Key words: ammonia toxicity, dissolved oxygen, rainbow trout, Salmo gairdneri

Morphological changes in the gills of Lophiosilurus alexandri exposed to un‐ionized ammonia

“…The un-ionized form of ammonia may be toxic to fish depending on factors such as pH variation (Thurston et al, 1981a), reduction of the dissolved oxygen level (Thurston et al, 1981b) and alterations in water temperature (Wajsbrot et al, 1993). In the present work, the values of pH, dissolved oxygen and temperature were maintained under control allowing the rate of NH 3 in the water to remain in the concentrations and ranges previously established.…”

“…Five different concentrations of NH 3 -N and one control (water with no ammonia chloride) were tested three times each in 18 aquaria of 20 l, each one containing 10 fishes of the same age group (Table I). Water pH was adjusted previously with solutions of 1·0 N NaOH and 1·0 N HCl (Thurston et al, 1981b) checked four times a day. The water temperature remained between 26 and 27 C and the rate of dissolved oxygen (Winkler method) was kept above 5·6 ml l 1 (65·7% of saturation) with the help of an air pump.…”

Relative sensitivities of common freshwater fish and invertebrates to acute hypoxia

“…Thus, chronic exposure of sensitive species to moderate DO concentrations (e.g., 3-5 mg litre-1 ) is likely to result in significant long-term impacts. Furthermore, toxicants are also known to increase the sensitivity of fish to low DO (Downing 1953;Lloyd 1961;Hicks & DeWitt 1971;Graves et al 1981;Thurston et al 1981). Although significant cumulative toxicological effects of acute and chronic hypoxia combined with two separate pulp and paper mill effluents were not seen in rainbow trout and common bully (Landman et al 2004, unpubl.…”

Assessment of Dredged Material Toxicity in San Francisco Bay

“…The percent of total ammonia present in the unionized form is significantly affected by factors such as pH, temperature, and to a lesser degree the ionic strength of the solution (e.g. hardness or salinity) (Thurston et al 1981b, Alabaster et al 1979, Emerson et al 1975, Whitfield 1974, Skarheim 1973.…”