The effects of carbon dioxide on growth performance, welfare, and health of Atlantic salmon post-smolt (Salmo salar) in recirculating aquaculture systems

Authors: MOTA, VASCO - Nofima; NILSEN, TOM OLE - Nofima; GERWINS, JASCHA - Nofima; GALLO, MICHELE - Wageningen University; YTTEBORG, ELISABETH - Nofima; BAEVERFJORD, GRETE - Nofima; KOLAREVIC, JELENA - Nofima; SUMMERFELT, STEVEN - Freshwater Institute; TERJESEN, BENDIK FYHN - Nofima

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2018
Publication Date: 1/1/2019
Citation: Mota, V., Nilsen, T., Gerwins, J., Gallo, M., Ytteborg, E., Baeverfjord, G., Kolarevic, J., Summerfelt, S., Terjesen, B. 2019. The effects of carbon dioxide on growth performance, welfare, and health of Atlantic salmon post-smolt (Salmo salar) in recirculating aquaculture systems. Aquaculture. 498:578-586. https://doi.org/10.1016/j.aquaculture.2018.08.075.
DOI: https://doi.org/10.1016/j.aquaculture.2018.08.075

Interpretive Summary: Compared to traditional flow-through aquaculture production systems, recirculation aquaculture systems (RAS) use water much more efficiently. However, because the water is intensively recirculated in RAS, carbon dioxide levels can increase. Excessive carbon dioxide levels are known to negatively affect fish growth performance, health, and welfare, but removal of carbon dioxide increases operational costs of RAS. This study aimed to identify effects of varying levels of carbon dioxide in RAS on fish growth performance, health, and welfare. Fish health and welfare indicators were not affected by carbon dioxide levels in this study, but growth performance, skin thickness, and the number of mucus cells on the skin were negatively affected by high levels of carbon dioxide. The results of this study allow producers to establish optimal levels of carbon dioxide that minimize operational costs of RAS while not affecting fish health, welfare, and growth performance.

Technical Abstract: High carbon dioxide (CO2) concentrations negatively impact fish, which makes data on its tolerance especially relevant for production systems that can accumulate CO2 such as recirculating aquaculture system (RAS). The current study evaluates the effect of CO2 on the growth performance, welfare, and health of Atlantic salmon postsmolts in RAS. This study consisted of two phases. The first was a CO2 exposure phase, where eighteen tanks were used with six treatments in triplicate: 5, 12, 19, 26, 33 and 40 mg/L of CO2 during 12 weeks in a 12 ppt salinity RAS (hereafter RAS phase). In the second phase, PIT-tagged fish were transferred to a 34 ppt salinity single flow-through tank at CO2 < 5 mg/L (hereafter seawater phase) for an additional 6-week experimental period mimicking a seawater phase. Overall, mortality of fish exposed to CO2 was low and not related to treatments. The mean final body weight was significantly higher in the 5 mg/L treatment compared to CO2 treatments =12 mg/L at the end of RAS phase and to CO2 treatments =33 mg/L at the end of seawater phase. Moreover, regressions showed that growth significantly decreased linearly with increasing CO2 in the water. Eye cataracts and visible external damage on skin, operculum, and fins were inexistent and similar among CO2 treatments. Kidneys showed no signs of mineral deposits in any of the structures of the tissue. However, skin analysis showed that fish exposed to high CO2 concentrations had a significantly thinner dermis layer (both at the end of RAS and seawater phase) and a significantly thinner epidermis layer and lower mucus cells count (at the end of seawater phase). In conclusion, Atlantic salmon post-smolts cultured in brackish water RAS showed a maximum growth performance at CO2 concentrations below 12 mg/L. Except skin, no major effects of health and welfare were observed, including cataracts and nephrocalcinosis. Further studies should evaluate the molecular and physiological responses to both short-term and long-term carbon dioxide exposure.