Effects of Water Reuse on Lake Trout

Lake trout (Salvelinus namaycush) were reared in water reused through a series of seven tanks for a period of 150 d. Fish loading per tank was based on a flow index of 0.71, giving a cumulative index of 4.97 after the seventh water use. Dissolved oxygen and total ammonia were measured as indicators of water quality. Average dissolved oxygen concentration decreased from 7.6 ppm after the first water use to 3.1 ppm after the seventh use, and average ammonia concentration increased from 0.09 ppm after the first use to 0.94 ppm after the seventh use. Lake trout growth rate began to decline at the fifth water use when dissolved oxygen averaged 3.5 ppm and ammonia 0.75 ppm.