| Summary: | Serial-pass raceway systems are characterized by reduced water quality as water passes from upper to lower raceways. We previously showed that rainbow trout reared in 1st use (source spring) and 3rd use (after 2 raceway passes) water exhibited significantly better growth and survival compared to those in 5th use water (after 4 raceway passes) and directly related to dissolved oxygen (DO) concentration. Our objective was to determine if increasing the DO in 5th use water by aeration or oxygenation to levels in 3rd use water could restore growth and survival of rainbow trout. We stocked rainbow trout (126 ± 9.3 g mean weight) into tanks receiving either 1st use, 3rd use, or 5th use water with and without supplemental air or oxygen (five treatments at four tanks each). Average DO concentration was highest in 1st use (92.0% saturation) followed by 3rd use (79.4%) and 5th use (52.1%) water. In 5th use water, use of aeration (68.4%) or oxygenation (71.7%) raised the DO levels similar to 3rd use water. Growth performance (SGR and FCR) and survival were significantly lower for trout in 5th use compared to 1st and 3rd use water. Aeration and oxygenation of 5th use water restored growth to that observed for trout in 3rd use water. Improvements were limited for survival with 3rd use water (88.8%) showing higher values than 5th use with oxygenation (74.2%) or aeration (53.1%). These treatments were still significantly better than survival observed for trout in untreated 5th use water (35.0%). Dissolved oxygen appears to be the primary water quality parameter limiting performance in this system. However, due to dissimilar survival in 3rd and 5th use water with aeration or oxygenation, other water parameters (e.g. total dissolved solids or turbidity), which increased in 5th use water, may also contribute to the reduced growth and survival. Keywords: Dissolved oxygen, Flow-through, Raceway, Rainbow trout
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