Fig. 6. Relative mRNA expression levels of gill Rh genes in excretory organs (gills and skin) of K. marmaratus exposed to 0 mmol l^–1 (control) or 1 and 2 mmol l^–1 NH₄HCO₃. (A) Gill RhBG, RhCG1 and RhCG2 relative to 18S rRNA. Asterisk indicates that RhCG2 mRNA levels were significantly higher than in fish exposed to 2 mmol l^–1 ammonia compared to 0 or 1 mmol l^–1 ammonia. RhBG and RhCG1 were not significantly different between control and ammonia-exposed fish. Values are means ± s.e.m.; 0 and 2 mmol l^–1 ammonia, N=7, 1 mmol l^–1 ammonia, N=8; one-way ANOVA, P<0.05). (B) Skin RhBG, RhCG1 and RhCG2 relative to EF1a. Letters (a,b,c) indicate that RhCG1 mRNA levels were significantly higher in fish exposed to 1 mmol l^–1 relative to 0 mmol l^–1 ammonia, and significantly higher in 2 mmol l^–1 relative to 0 and 1 mmol l^–1 ammonia. Asterisk indicates that RhCG2 was significantly higher in 1 mmol l^–1 compared to 0 and 2 mmol l^–1 ammonia. RhBG was not significantly different between control and ammonia-exposed fish. Values are means ± s.e.m.; N=6 (one-way ANOVA, P<0.05).