A comparison of methods of measuring chromatic activity in the integument of a teleost

1. Pallor induced by noradrenalin (5 x 10(-7) mol/kg) injection of dark Pseudopleuronectes americanus was measured as increase in skin reflectance and the degree of melanosome aggregation determined. 2. Mean skin reflectance increased approximately 30% on the Munsell neutral value scale. 3. At maximal mean reflectance, melanosomes were fully aggregated in most epidermal melanophores, but displayed more variable aggregation in dermal melanophores. 4. Individual reflectance estimates did not provide consistent indications of melanosome aggregation at maximum pallor. 5. The relative merits of reflectance and cellular methods of estimating melanophore activity are discussed with particular reference to this species.