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Laronde, Daniel

University of British Columbia

Atlantic salmon (Salmo salar) undergo a drastic change of environment during their lifecycle as they go from being salt-limited in freshwater to being water-limited in seawater. Fish prepare for this challenge by increasing various methods of water uptake and ion secretion. Currently the aquaculture industry prepares salmon for seawater entry by simulating the shift from a winter photoperiod to a summer photoperiod before transferring them into marine net pens at ~150g. Fish are then grown to the market size of ~4kg over the following 12-18 months. The marine net-pen environment is unpredictable and prone to high mortality events due to toxic algal blooms and periodic hypoxia, among other challenges. There is a strong interest on the part of the aquaculture industry in reducing the time salmon spend in net-pens by rearing them for longer in freshwater recirculating aquaculture systems to a much larger size prior to attempting to induce smoltification using photoperiod manipulations for seawater transfer. For this project, I aimed to use the industry standard light manipulation to generate fish that were ready for seawater entry at ~200g, ~500g, and ~1kg. Each size class had photoperiod-manipulated (PT) fish and control (C) fish to determine whether the light manipulation used in industry is effective in preparing salmon for seawater entry at larger sizes. Fish in seawater must drink water to offset passive water loss, so I measured drinking rates and plasma osmolytes to ask whether the amount that they drank was sufficient. As the intestine is a largely overlooked osmoregulatory organ, I investigated 3 different regions (proximal, mid, and distal intestines) of the intestine and measured Na⁺/K⁺-ATPase (NKA) activity to inform on the importance of photoperiod manipulation in growing larger fish for seawater transfer. Drinking rate did not differ between the PT and C fish, but did increase upon seawater transfer and was accompanied by adaptive changes in plasma osmolytes. NKA activity overall did not differ between treatments, but an increase in hindgut NKA activity was measured upon seawater transfer. The results of this thesis support the transfer of Atlantic salmon into the marine environment at larger sizes.

Text

2023-12-14

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86958

Zoology

University of British Columbia

UBCV

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