Toxicity of ammonia to early life stages of rainbow trout ( Salmo gairdneri)

Abstract

The toxicity of ammonia to early life stages of rainbow trout ( Salmo gairdneri) was examined in hard fresh water. When exposure began within 24 h of fertilisation and proceeded for 73 days, severe mortality (> 70%) occurred, particularly among the eggs, at concentrations of unionised ammonia as low as 0.027 mg l −1 as NH 3. When exposure did not start until the eyed-egg stage (c. 24 days) only 40% of the eggs, yolk-sac fry and fry (but especially the fry) died at 0.27 mg l −1 as NH 3. Both the standards proposed for protecting fish communities and the protocols drawn up for assessing the effects of chemicals should take into account the sensitivity of early life stages of freshwater fish. In particular, in evaluating chemicals, exposure should begin as soon as possible after fertilisation.