RAINBOW-TROUT LIVER ACTIVATION SYSTEMS WITH THE AMES MUTAGENICITY TEST

A poikilothermic metabolic activation system developed from liver homogenate of rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri) was used in the Ames Salmonella/Mammalian Microsome Mutagenicity Test. Postmitochondrial fractions (S9) mediated four model promutagens – 2‐aminoanthracene (2AA), 2‐aminofluorene (2AF), benzo[a]pyrene (BaP) and 3‐methylcholanthrene (3MC)–that require two different exogenous metabolic activation routes to form mutagens with Salmonella TA98 and TA100. The enzymatic activity of trout S9 was cytochrome P‐450‐like; it was heat labile and oxygen‐ and cofactor‐dependent. Preincubation temperature significantly influenced the sensitivity of the fish‐activated Ames test. Bacterial mutagenesis with trout activation significantly decreased as preincubation temperature increased; the optimum S9 activation temperature range for trout was 10 to 15°C compared with 37°C for the rat. The liquid‐preincubation test was best adapted to the trout poikilothermic activation system; it was significantly more sensitive than the plate‐incorporation test in detecting histidine revertants. The S9 activity of trout and rat was qualitatively similar in the Ames test: that is, both fractions metabolically activated 2AA, 2AF, BaP and 3MC to produce bacterial mutagenesis with Salmonella TA98 and TA100. The use of this ecologically relevant exogenous activation system in the short‐term predictive genotoxicity testing of freshwater ecosystems is helpful in the assessment of potential hazards of chemical contaminants on fishery resources. Copyright © 1990 SETAC