The effects of salinity and photoperiod on growth and swimming performance in Atlantic and coho salmon raised in recirculating aquaculture systems from smolt to adult.

Salmon are among the most popular seafood products and their culture continues to expand with improved aquaculture technology. Typical aquaculture production rears salmon from smolt to market size in net-pens in oceans, but this practice has been criticized due to potential environmental concerns such as eutrophication and interactions between escaped cultured fish and wild populations. Rearing fish in recirculating aquaculture systems (RAS) is a new technology to address some of the concerns over net-pen aquaculture, as well as enhance production of salmonids and other fish species. Salmon can inhabit a wide range of salinities with different osmoregulatory costs, but presumably these costs can be reduced if fish reside in water isosmotic to their blood plasma. Photoperiod has been shown to affect growth rates in salmon at different life stages but can also affect early maturation in salmon. To examine the effects of salinity and photoperiod on the growth of salmon, seven replicate RAS with salinities of 2.5, 5, 10 and 30ppt under 12:12 and 24:0 light:dark photoperiod were used to rear Atlantic and coho salmon from smolts onwards for 120 days. Salinity and photoperiod had an effect on Atlantic salmon growth, with those reared at 10ppt in 24:0 light showing the highest growth rates. However, neither photoperiod nor salinity affected coho salmon growth. To understand the effects of salinity and photoperiod on swimming performance and hematology, coho salmon from two separate studies underwent repeat maximum swimming speed (Umax) tests. In the first study, Umax was assessed in coho salmon that were reared for 350 days in 0 and 10ppt. In the second study, Umax was assessed in coho salmon that were reared for 60 and 150 days in 2.5, 10 and 30ppt under 12:12 and 24:0 light:dark photoperiod. In the first study, salinity had significant effects on resting plasma osmolality and chloride concentration. In the second year, salinity affected first Umax, but neither salinity nor photoperiod affected repeated Umax and recovery ratio. There were also significant effects of salinity on the hematocrit, hemoglobin concentration, MCHC and plasma osmolality and chloride concentration of exhausted salmon after repeated swimming tests.Science, Faculty ofZoology, Department ofGraduat