Fig. 4. Relationship of muscle urea content with total methylamine (closed symbols, solid line) or combined total of methylamine and ß-amino acid (open symbols, broken line) content in marine (circles), euryhaline species in freshwater (FW) (triangles) and freshwater elasmobranchs (squares). Values are mean ± s.e.m. and N values are the same those for total methylamine contents in Fig. 4. The regressions are statistically significant (total methylamines, P<0.01; total methylamines plus ß-amino acids, P<0.001).