the acute neurotoxic effects of s,s,s,-tri-n-butyl phosphorotrithioate (def), widely used as a cotton defoliant in the us, on juvenile channel catfish and adult blue crabs were examined using short-term exposures in aerated, static aquaria. the effects on acetylcholinesterase (ache) activity in catfish brain and skeletal muscle and in crab ganglia were studied. in addition, recovery of ache activity was followed after transferring the animals to def-free water. the results indicate that both species exhibit pronounced anticholinesterase effects due to def. recovery of ache activity is quite slow in nervous tissues of both animals and catfish skeletal muscle, with effects persisting for several weeks following a single acute exposure. tissue levels of def, as well as its rate of disappearance, were followed in several tissues of each species. the highest levels were detected in fish liver, but high levels were also detected in fish brain. (edited author abstract) 33 refs