Abstract In Portugal, large quantities of kraft pulp mill effluents are discharged into the river Vouga by the Portucel kraft pulp mill factory in Cacia. Sublethal effects of pollutants are useful in assessing the physiological response to a particular toxic effluent by a particular species as an adaptive response. How do survivors recover after exposure? This research work shows how Anguilla anguilla L. responds to a 4-h exposure to 50 and 100% BKPME (Bleached Kraft Pulp Mill Effluent) followed by 8 days of recovery in filtered, dechlorinated, aerated tap water. The 4 h exposure to either 50 or 100% BKPME shows a significant increase in plasma lactate. Plasma glucose is not significantly affected by any of the previous exposures. After 8 days of recovery, the eel's plasma lactate decreased significantly compared to control values in both conditions. However, glucose decreased significantly in the eels recovering from a previous exposure to 100% BKPME.