Fig. 10. Plasma cortisol levels after 12 h of exposure to 1% CO₂ in air (CO₂), 1% CO₂ in air with 10 mmol l^–1 Hepes-buffered water (CO₂+Hepes), 100% air with 10 mmol l^–1 Hepes-buffered water (Air+Hepes) and high environmental ammonia (HEA; 1.5 mmol NH₄HCO₃). Control fish were exposed to 100% air for 12 h in unbuffered water. Asterisk indicates significant difference from the control value (P<0.05). Data are means ± s.e.m. (N=6–10).