Fig. 1. Carnitine palmitoyl transferase (CPT) activities (mean ± s.e.m.) in liver and extrahepatic tissues of freshwater, euryhaline and marine elasmobranchs with varying levels of urea: Potamotrygon motoro (freshwater) (no urea), Himantura signifer in freshwater (low urea), H. signifer acclimated to half-strength seawater ( Seawater) (increased urea), Taeniura lymma (marine) (high urea), and Chiloscyllium punctatum (marine) (high urea). See text or Fig. 4 for specific urea levels. Sample sizes and the results of statistical comparisons between tissues and species are given in Tables 1 and 2. The salinity (and thus urea level) for each species or acclimation group is indicated by the shading of the bars. Enzyme measurements were made at 25°C. ND, not detectable.