CHRONIC EFFECTS OF LINEAR ALKYLBENZENE SULFONATE (LAS) AND AMMONIA ONRAINBOW-TROUT (ONCORHYNCHUS-MYKISS) FRY AT WATER CRITERIA LIMITS

Rainbow trout fry was chronically exposed (54 days) to 0.2 mg l(-1) LA S(C-11-12) Although this concentration is considered to be the NOEC (n o observed effect concentration), lamellar gill epithelia hypertrophie d and swimming capacity was reduced. Furthermore, the exposure of the fish to a secondary stressor (low salinity challenge test) caused incr eased mortality. Un-ionized ammonia did not affect the above-mentioned parameters when fish were treated with a NOEC of 24 mu g l(-1). At 72 mu g l(-1), however, un-ionized ammonia caused distinct hypertrophy o f gill epithelia. This effect was significantly enhanced when combined with LAS (additive effect). Only in this group, growth was reduced.