Fig. 4. Relationship between white muscle urea concentration and liver glutamate dehydrogenase (GDH) activity in elasmobranchs. Values are mean ± s.e.m. See text for full names of species. Error bars for GDH in Potamotrygon motoro and P. magdalenae are asymmetrical to avoid overlapping bars. ¹GDH values are from the present study (see Table 1 for sample sizes) and urea values are from the same animals (N=5–8, taken from various studies) (Treberg et al., 2006). ²GDH value (Singer and Ballantyne, 1989); urea value was assumed to be the same as in P. motoro (Treberg et al., 2006). ³GDH value (Moon and Mommsen, 1987); urea value (Forster and Goldstein, 1976). ⁴GDH value (Battersby et al., 1996); urea value (Treberg and Driedzic, 2002). GDH activities for spiny dogfish and little skate were adjusted to 25°C using Q₁₀=2. The regression is significant (r=0.93, P<0.001, linear regression ANOVA).