Effects of rearing system on growth responses and saltwater tolerance in spring Chinook Salmon (Oncorhynchus tshawytscha).

Pacific salmon (Oncorhynchus spp.) produced in United States conservation hatcheries are commonly reared in tanks and raceways supplied with single-pass water. As controlled studies comparing water reuse vs. traditional single-pass aquaculture systems are limited, we conducted a 20-week growth trial followed by a one-week saltwater challenge to compare growth, survival and saltwater tolerance of juvenile spring Chinook salmon (O. tshawytscha , 5.2 g initial weight) reared in single-pass rectangular tanks (hereafter rectangular tanks), single-pass circular tanks (hereafter circular tanks), or in circular tanks of recirculating aquaculture systems (RAS, 3% constant makeup water on a flow basis) or partial recirculating aquaculture systems (PRAS, 20% constant makeup water on a flow basis). Water volume provided to rearing tanks did not differ among systems, but water velocities in the circular tanks and in the RAS and PRAS fish culture tanks were higher than in the rectangular tanks. Dissolved oxygen levels declined throughout the study in all systems and were significantly lower in RAS than in the single-pass systems. By week 16, ammonia levels were significantly reduced while nitrite‑nitrogen (NO 2 -N) and nitrate‑nitrogen (NO 3 -N) levels were significantly elevated in RAS compared with single-pass systems. Salmon grown in rectangular tanks exhibited significantly lower weight gain and feed efficiency (FE; g gain/g feed) compared with fish reared in the other systems. Survival of salmon grown in the rectangular tanks (99.1%) also was significantly lower than that of fish reared in circular tanks (100%) or PRAS (100%), but was not different from that of fish reared in RAS (99.8%). Survival during the saltwater challenge was significantly reduced in salmon that were reared during the growth trial in rectangular tanks (70%) compared with that of fish that were reared in the other systems (92–96%). Results of this study suggest lower growth and survival of salmon reared in rectangular tanks may be related to reduced water velocity and that RAS and PRAS may be appropriate for rearing spring Chinook salmon for conservation purposes. • Rearing Chinook in a reuse system required 21-fold less well water than control tanks. • Growth of Chinook in reuse systems did not differ from that of fish in circular tanks. • Growth of Chinook in reuse systems was higher than that of fish in rectangular tanks. • Results suggest reuse systems may be appropriate for rearing Chinook salmon. [ABSTRACT FROM AUTHOR]

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