Zebrafish, like other teleosts, display rapid skin color change in response to the background through sympathetic nerves. Here, the alpha-and beta-adrenoceptors of melanophores were studied pharmacologically both in zebrafish embryo and adult scale. In vitro experiments on adult scale melanophores demonstrated that both alpha(1)- and alpha(2)-adrenoceptors are functional in melanosome aggregation, the alpha(2) subtype being predominant. Most melanophores in zebrafish embryos were able to concentrate melanosomes to alpha(2)-adrenergic agonist alpha-methylnorepinephrine when they first appeared. This ability increased at least in the following 48 h, showing melanophores at these stages have developed functional adrenoceptors and these receptors increase independently before sympathetic innervation. However, even high concentration (10(-3) M) of alpha(1)-adrenoceptor agonist phenylephrine was not able to evoke any paling of the embryos. In adult scales, propranolol enhanced the melanosome-aggregating response of epinephrine and isoproterenol, but not norepinephrine, indicating p-adrenoceptor mediates melanosome-dispersing response in adult zebrafish. Similar response was not observed in embryos until 60 h post-fertilization (hpf). The melanophore adrenoceptor blocking effects of phentolamine and propranolol in embryos were much lower than that in adult zebrafish, suggesting these adrenoceptors in developing melanophores are less sensitive to the classical antagonists. (C) 2011 Elsevier Inc. All rights reserved.