Effect of Reused Water on Brown Trout

Abstract

Brown trout fingerlings (Salmo trutta) were reared for 141 d in water that passed successively through a series of seven troughs. Fish loading per trough was based on a flow index of 36.4, thus the cumulative index was 254.8 at the seventh water use. Two indicators of water quality were measured after each water use; average dissolved oxygen concentration decreased from 7.6 mg/L after the first water use to 3.6 mg/L after the seventh use, and average total ammonia concentration increased from 0.1 mg/L to about 0.9 mg/L. Growth rate began to decline at the fourth water use, when dissolved oxygen averaged 4.8 mg/L and total ammonia averaged 0.6 mg/L.