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Title: The effects of carbon dioxide on performance and histopathology of rainbow trout Oncorhynchus mykiss in water recirculation aquaculture systems

item GOOD, CHRISTOPHER - Freshwater Institute
item DAVIDSON, JOHN - Freshwater Institute
item WELSH, CARLA - Freshwater Institute
item SNEKVIK, KEVIN - Washington State University
item SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2009
Publication Date: 3/1/2010
Citation: Good, C., Davidson, J., Welsh, C., Snekvik, K., Summerfelt, S. 2010. The effects of carbon dioxide on performance and histopathology of rainbow trout Oncorhynchus mykiss in water recirculation aquaculture systems. Aquacultural Engineering. 42:51-56.

Interpretive Summary: We examined the effects of prolonged, moderate (~25mg/L) dissolved CO2 exposure on rainbow trout raised to market size in high feeding, low flushing water recirculation aquaculture systems (WRAS). Elevated CO2 levels in aquaculture have been associated with poor growth, increased mortality, and poor feed conversion; however, the additional water pumping costs when attempting to reduce CO2 levels in rearing units also must be considered by producers trying to balance fish health with profitability. We raised rainbow trout from <100g to market size in six replicated WRAS (three with 25 mg/L and three with 10 mg/L CO2) over 6-months. Our findings demonstrate that rainbow trout perform just as well in high CO2 systems than low CO2 controls: average final fish weight was not effected, survival was comparable, and no pathologies were noted. It is therefore likely that producers who attempt to reduce comparable levels of dissolved CO2 through pumping water can actually realize comparable fish growth without the additional pumping costs.

Technical Abstract: Chronic exposure to elevated levels of dissolved carbon dioxide (CO2) has been linked to reduced growth, physiological disturbances and negative health outcomes in intensively reared fish. Although pumping to a degassing tower can lower concentrations of dissolved CO2 in water recirculation aquaculture systems (WRAS), pumping can be a significant cost for operators. A six-month trial was conducted to compare the effects of high (24 +/- 1 mg/L; partial pressure = 8.79 mm Hg) and low (8 +/- 1 mg/L; partial pressure = 2.91 mm Hg) dissolved CO2 concentrations on rainbow trout Oncorhynchus mykiss performance and health in replicated WRAS operated at low exchange rates (0.26% of the total recirculating flow). Rainbow trout (62 ± 1 g) were randomly stocked into six replicated WRAS and into three small tanks within a flow-through system to provide a physiological comparison. All study fish were maintained at densities between 25 kg/m3 and 80 kg/m3, at water temperatures of approximately 13-14 oC, and at dissolved oxygen concentrations of approximately saturation. A 24-hour photoperiod was provided and all fish groups were fed equal portions every two hours during the study period. Fish health and performance were assessed with daily mortality and monthly length and weight data collection, as well as multiple tissue samplings for histopathological assessment. At study's end, percentage survival for both groups was high (>97%). No significant (p<0.05) differences in growth or survival were observed between CO2 treatments. No nephrocalcinosis or related pathologies were noted. Skin and gill pathologies were common in both treatment groups; however, there were few statistically significant differences between groups for any of the tissue types evaluated: high CO2 fish were more likely to exhibit lymphocytic portal hepatitis, while the low CO2 treatment group exhibited greater gill epithelial hyperplasia. None of the pathologies observed were substantive or likely to cause mortality. The results of this study indicate that raising rainbow trout to market size in WRAS with CO2 concentrations of 24 mg/L does not significantly affect their overall health and performance.