Production of market-size North American strain Atlantic salmon Salmo salar in a land-based recirculation aquaculture system using freshwater

There is interest in culturing Atlantic salmon Salmo salar to market-size in land-based, closed containment systems that use recirculation aquaculture systems (RAS), as this technology often enables facilities to locate near major markets, obtain permits, exclude obligate pathogens, and/or reduce environmental impacts. Use of land-based RAS to intensively culture market-size Atlantic salmon is a relatively new frontier and little information is available. Three trials were conducted to evaluate the performance of two North American strains of Atlantic salmon raised from post-smolt to market-size (4-5 kg) in a near-commercial scale (260 m3), land-based RAS using only freshwater. St. John River (SJR) salmon were reared during the first trial, and Cascade salmon (CS1 and CS2) were evaluated during two subsequent trials. Salmon were received as fertilized “eyed” eggs and cultured on-site through the entire production cycle. The grow-out period began at 14-16 months post-hatch when salmon post-smolt weighed 0.34-0.75 kg on average. CS1 and SJR salmon grew 386-393 g/month to a mean size of 4.1-4.2 kg and CS2 salmon grew 413 g/month to a mean size of 4.9 kg prior to first harvest. Thereafter, weekly salmon harvests commenced for the next 6-19 weeks. The grow-out period, excluding harvest, lasted 9-10 months for each trial. Average water temperature was maintained at 15-16 °C. Consistently linear growth rates were achieved by each population suggesting that growth was relatively independent of fish cohort/genetic strain, fish size, and maximum biomass density, which was 35, 100, and 118 kg/m3 for SJR, CS1, and CS2, respectively. Feed conversion ratios ranged from 1.07 to 1.10. Fish mortality (including culls) for SJR, CS1, and CS2 was 9.5, 6.6, and 7.5% of the original number of stocked fish, respectively. No obligate fish pathogens, kudoa, sea lice, or pervasive parasites were detected. Salmon were not vaccinated against specific pathogens; and no antibiotics, pesticides, or harsh chemotherapeutants were used. Hydrogen peroxide (50-100 ppm) and salt (10 ppt) were occasionally used to treat fungus during pre-smolt production, and salt (2-3 ppt) was used to treat fungus or ameliorate stress after handling events. No salmon escaped the facility due to built-in fish exclusion barriers. Early male maturation was observed during each trial. Male salmon began to exhibit maturation traits (kype, darkened skin coloration) at a mean weight of 1.5-2 kg and were removed from the grow-out system when they weighed 2-3 kg. SJR, CS1, and CS2 populations exhibited 37.0, 38.5, and 17.0% maturity, respectively. Fillet yield and product quality of immature, market-size salmon were comparable to reported measurements for commercially available salmon reared in net pens. This research suggests that it is biologically and technologically feasible to culture Atlantic salmon from post-smolt to market-size in a land-based RAS of suitable commercial scale; however, early male maturation could represent a production barrier. As of 2016, all-female Atlantic salmon eggs are commercially available and could provide an expedient solution to the problem of early male maturation in RAS.