Fig. 6. The effect of the nitric oxide generator DEANO (10^–6 mol l^–1) on clearance. Data are ratios of the treatment rate (rate of clearance after a 15 min exposure to DEANO) to the unstimulated basal rate. Data are means ± s.e.m. Treatments: none, untreated controls (N=39); DEANO (w), gills exposed to DEANO during the winter (N=17); DEANO (s), gills exposed to DEANO during the summer (N=18). The mean during the winter is significantly greater than the untreated controls (P<0.05).