Fig. 4. The effect of 12 h exposure of rainbow trout to: hypercapnia (1% CO₂ in air) in unbuffered water, hypercapnia in 10 mmol l^–1 Hepes-buffered water, and normocapnia (100% air) in Hepes-buffered water on the net ammonia flux (J_Amm). Control fish were exposed to normocapnia for 12 h in unbuffered water. The negative values indicate excretion into the water. Crosses represent values significantly different from the 3 h control value. Asterisks represent values significantly different from the 12 h control value. Control values are significantly different from each other (P<0.05). Data are means ± s.e.m. (N=6–10).