EVALUATION OF BIS(TRI-N-BUTYLTIN)OXIDE (TBTO) NEUROTOXICITY IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) .1. BEHAVIOR, WEIGHT INCREASE, AND TIN CONTENT

Three-week old rainbow trout hatchlings (Oncorhynchus mykiss) were exp osed to 0.5 mug/l or 2.0 mug/l bis(tri-n-butyltin)oxide (TBTO) for 21 days in a flowthrough system. After 7 and 21 days, weight increase was determined, swimming behaviour was recorded and samples were taken to determine tin content by atomic absorption spectrophotometry. Bioaccu mulation of TBTO, reduced weight increase and accumulation of tin in b oth fish trunk and head were dose-dependent. Fish concentrated TBTO fr om the surrounding water by a factor of up to 900. After 21 days, incr ease in weight was drastically reduced in fish treated with 2 mug/l TB TO over control fish. In comparison to control fish, TBTO-treated fish swam greater distances for longer time and with greater speed. Wherea s control fish showed conspicuous orientation along the wall of the ci rcular aquaria, swimming tracks of TBTO-exposed rainbow trout do not s how this orientation.