To explore the effects of phenol on the carbohydrate and protein metabolism,Moina macrocopa were exposed to phenol(0.25,0.75,1.25,1.75,2.25 mg /L) for 24 and 48 hours.Activities of several key metabolic enzymes including pyruvate kinase(PK),lactate dehydrogenase(LDH),succinate dehydrogenase(SDH),glutamic oxaloacetic transaminase(GOT) and glutamic pyruvic transaminase(GPT) were investigated.The results showed that the activity of LDH was gradually increased following the increase of phenol concentration and treatment duration.PK and SDH activities remained almost unchanged.After 24 h,the activity of GOT firstly showed increase,and then decrease.After 48 h,the activity of GOT decreased.The activity of GPT was slightly elevated,but there was no significant difference when compared with controls.All these results indicate that phenol intoxication demands high level metabolic energy and leads to significant changes of the metabolic profile of the daphnia,inducing to a certain extent a shift from carbohydrate catabolism to protein catabolism.The LDH may serve as a biomarker of aquatic animal for assessing the biochemical toxicity of phenolic contamination.