The use of a compact recirculation system for rearing rainbow trout is described. An 8-month experiment showed that up to 75 kg offish could be maintained in a healthy condition in a 1600-liter tank using a make-up water rate of only 1.0 liter/min. Temperature, oxygen, pH, ammonia nitrogen, and nitrate nitrogen levels were satisfactorily controlled. An average weight gain of 8% per week was achieved with a feed rate of 2% of body weight per day. Fish mortality was insignificant.