Physiology and Pharmacology of Color Change in the Sand Flounder Scopthalamus Aquosus1

An elucidation of the mechanisms of chromatophore control in teleost fishes involves consideration of the participation of the nervous system (pigment concentrating and dispersing fibers) and an evaluation of influences mediated by pituitary hormones. The sand flounder, Scopthalamus aquasus Norman (Lophosetta muculatu Gill) was investigated by neurological and pharmacological methods. Nerve cutting, blocking and stimulation experiments revealed unequivocally functional pigment aggregating but not dispersing fibers. Acetyl choline and eserine when injected into the spinal cord bring about excitation of pigment concentrating nerve fibers but have no local effect on melanocytes. Drugs causing local pigment aggregation are aromatic ethyl amines or hydrazines. Epinephrine, norepinephrine and dopamine are extremely active. The most potent pigment dispersing drugs were certain phenothiazine tranquilizers. Pretreatment with pyrogallol markedly potentiated epinephrine and norepinephrine but raised the effective dose of five of the drugs having pigment dispersing properties. The pharmacological data suggest a catechol amine as the transmitter at concentrating nerve fiber endings, and that the enzyme catechol‐o‐methyl transferase is involved in the physiology of color change in the sand flounder.