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MacKinnon, Rachael

University of British Columbia

Atlantic salmon aquaculture utilizes land-based freshwater recirculating aquaculture systems (RAS) and marine net pens. In freshwater (FW), industry rears salmon under continuous light (24L:00D) at 14℃ before initiating an artificial winter photoperiod of 12L:12D for 2 months and switching back to 24L:00D for 1 month. This induces smoltification, which is critical in preparing salmon for seawater (SW) transfer. Developing larger, more physiologically robust smolts is an industry goal, to reduce time spent in net pens, while yielding higher growth rates and survival. Using five independent RAS, I developed ~200g, 700g, and 1400g smolts using the same photoperiod regimen as industry, in addition to SW transfer for to 2 months under 24L:00D. Fish were characterized as "treatment", exposed to an artificial winter photoperiod, or "control" kept under continuous light. Blood, gill, and muscle tissue samples were collected at specific timepoints in FW and SW to evaluate key indicators of smolt status (blood hemoglobin, hematocrit and mean cellular hemoglobin content, plasma ions, gill Na+/K+-ATPase activity, and muscle water content) across the different size groups. Additional measurements of gonadosomatic and hepatosomatic index were taken to assess maturation status. Tissue and blood samples were also collected to assess if the 1 month duration in 24L:00D used for salmon aquaculture following a winter photoperiod is effective in inducing optimal smoltification. To address this, fish were kept in FW for 2 and 3 months under 24L:00D following the 12L:12D treatment and then transferred SW 24h. Despite observing modest effects of the photoperiod manipulation, all size groups displayed exemplary SW tolerance upon SW transfer, with low mortality. Additionally, extending the duration of the FW period to 2 or 3 months did not increase smolt robustness when compared to the industry standard of 1 month. These findings suggest that while artificial photoperiod manipulations may not be necessary for the development of larger Atlantic salmon smolts, further research is required to better understand their impact on the physiological performance of larger salmon during SW transfer. Additionally, future research should address potential confounding variables, such as precocious maturation, as previous studies have suggested it may interfere with the smoltification process.

Text

2024-05-03

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88173

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/