Elevated CO₂ is a common water-quality challenge in recirculating aquaculture systems. Although its effects are often accompanied by environmental acidification, the direct impact of elevated CO₂ under stable-pH conditions on fish olfactory function remains poorly understood. This study investigated the effects of elevated CO₂ on olfactory function and olfactory epithelial homeostasis in juvenile largemouth bass (Micropterus salmoides). Fish were exposed to approximately 5 mg L−1 (control), 10 mg L−1, and 15 mg L−1 CO₂ for 4 days while maintaining stable pH. Olfactory function and olfactory epithelial responses were evaluated using behavioral assays, calcium imaging, histological analyses, Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, immunofluorescence, and gene-expression analyses. Exposure to 10 and 15 mg L−1 CO₂ significantly reduced attraction to food odor without affecting swimming activity, indicating impaired olfactory sensitivity. Calcium imaging revealed attenuated olfactory responses to L-alanine, accompanied by altered expression of genes involved in olfactory signal transduction. Elevated CO₂ also increased the number and area of acidic mucous cells, reduced the abundance of mature olfactory sensory neurons, increased apoptosis in the olfactory epithelium, and altered the expression of genes associated with apoptosis, cell proliferation, and neurogenesis. These findings indicate that elevated CO₂ under stable-pH conditions impairs olfactory function and disrupts olfactory epithelial homeostasis in juvenile largemouth bass. The present study demonstrates that dissolved CO₂, independent of environmental acidification, adversely affects the fish olfactory system and highlights the importance of monitoring CO₂ as a key water-quality parameter in recirculating aquaculture systems.
Gong Z., Niu H., Xiang X., Zhang G., Huang M., Liu F., Lv J. & Wang X., 2027. High CO2 at stable pH disrupts olfactory homeostasis and function in largemouth bass. Aquaculture 627(1): 744493. doi: 10.1016/j.aquaculture.2026.744493. Article (subscription required).
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