Introduction
The growing land-based salmon industry, utilizing recirculation aquaculture system (RAS) technologies, has largely focused on producing Atlantic salmon Salmo salar. In the United States, there are presently only two such facilities raising alternative salmonid species – steelhead trout Oncorhynchus mykiss and coho salmon Oncorhynchus kisutch. While steelhead trout production benefits from decades of selective breeding efforts, an abundance of performance data, and year-round egg availability, coho salmon is a relatively unstudied species. Nonetheless, there is significant interest from RAS stakeholders in coho salmon as an alternative salmonid species with considerable market potential. Early efforts in raising coho salmon in RAS in the U.S. demonstrated disappointing growth performance well below targeted levels due to suboptimal rearing environments; however, more recent advances in rearing protocols have shown that excellent growth performance can be achievable in RAS. Nonetheless, optimized culture conditions for coho salmon production in RAS still need to be defined.
Materials and methods
All-female diploid coho salmon eyed eggs were obtained from a U.S. commercial supplier and hatched in Heath trays within a RAS incubation system maintained at 8-10 oC. After the sac fry has absorbed the majority of their yolk sacs, they were transferred to six 0.5 m3 tanks in a flow-through system (approximately 13.5 oC). Following normal industry protocols, all salmon were raised under a natural, rising photoperiod (Campbell River, BC, Canada latitude) from hatch until 30 weeks post-first feeding, in order to instigate smoltification beginning at approximately 50 g. At 30 weeks post-first feeding, the entire population was bottom-culled to eliminate fish that failed to undergo smoltification. Fish remained on natural photoperiod in the flow-through system until a mean weight of 600 g was achieved, after which they were transferred to six replicated RAS (9.5 m3 total volume; 5.3 m3 tanks) maintained at either 14 oC or 17 oC, with n=3 replication for high vs. low-temperature treatments. All fish were fed standard diets from a commercial supplier for the duration of the study; feed amounts provided to each study tank over the course of the experiment were based on standard industry feeding charts, but were adjusted based on feeding activity such that fish were fed to satiation. All RAS were operated at an exchange rate that facilitated 17 oC water temperature, with chillers being employed in the lower temperature group to achieve 14 oC in those specific RAS. Throughout the study period, fish performance was / will be assessed bimonthly, quantifying length, weight, dorsal and caudal fin condition, and cataract scores from a representative sample of fish per tank. The study will be completed once the best-performing treatment group attains a mean weight of 3 kg (i.e., the targeted industry harvest size). Aside from the performance outcomes listed above, maturity will be assessed via gonadosomatic index calculation from a representative sample of fish from each tank, and viscerosomatic indices will be quantified to assess coelomic adipose deposition. Mean condition factor and population coefficient of variation (weight) will be calculated at each sampling point, and specific growth rate, thermal growth coefficient, and feed conversion will also be assessed. Background water chemistry for relevant RAS parameters (alkalinity, BOD, hardness, pH, NO2-N, NO3-N, total phosphorus, TSS, true color, and turbidity) are being regularly assessed throughout the study period.
Results
At the time of abstract submission, the most recent sampling event was carried out at around 1 kg mean weight, and final sampling at 3 kg is projected to be completed in June-July 2025. Presently, no clear differences in the performance, health, and welfare metrics listed above have been noted between the two treatment groups; however, all final results will be presented at Aquaculture Europe 2025.