The fish toxicity data were used for predicting the toxicity categories via both the conventional QSAR regression model and the direct classification strategies. The QSAR regression model resulted in predicted LC50 values that were converted to the two types of acute fish toxicity categories in a subsequent step. On the other hand, the classification model directly predicted the toxicity categories. The predicted acute fish toxicity categories based on both methods were compared to the true categories coming from the measured 96h LC50 values for fish toxicity to evaluate the accuracy of each approach.