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Silver sea bream Sparus sarba is a euryhaline marine teleost.Euryhalinity is dependent on the existence of several ion transporters and enzymes which are strategically located at various osmoregulatory epithelia such as gill and kidney.In freshwater (FW), one important component is carbonic anhydrase (CA).We have purified CA from the gill and used it to generate a rabbit polyclonal antibody with high specificity to sea bream CA.Immunohistochemical studies have shown intense localization of CA in gill chloride cells (CC), suggesting involvement of CA in salinity adaptation.Regarding Cl secretion, euryhaline fish possesses a cystic fibrosis transmembrane conductance regulator (CFTR) Cl channel.The CFTR gene sequence was obtained from sea bream gill (GenBank no: EF017215) from which specific oligonucleotides were obtained for detection of CFTR mRNA expression in osmoregulatory tissues.High CFTR expression was observed in the gill, which is consistent with high abundance of CCs in the branchial tissue.CFTR was also abundantly expressed in the sea bream pituitary but its significance is anomalous since the fish pituitary is known to produce prolactin, the major FW-adapting hormone, and also that of growth hormone, the seawater adaptation hormone.Further experiments are required to elucidate the physiological significance of CFTR in the fish pituitary.