Channel catfish (Ictalurus punctatus) proopiomelanocortin (POMC) cDNA was cloned to investigate its structure, evolution, and expression in different tissues. POMC is an important gene in the hypothalamus-pituitary-adrenal axis, the main mediator of the stress response. POMC gene was isolated from a pituitary cDNA library and nucleotide sequence was determined. POMC cDNA is composed of 1164 nucleotides with a 639 nucleotide open reading frame encoding a protein of 212 amino acids. Catfish POMC protein contains a signal peptide (SP, Met(1)-Ala(28)), N-terminal peptide (Gln(29)-Glu(101)), adrenocorticotropic hormone (ACTH, Ser(104)-Met(142)), alpha-melanocyte stimulating hormone (alpha-MSH, Ser(104)-Val(116)), corticotropin-like intermediate lobe peptide (CLIP, Arg(121)-Met(142)), beta-lipotropin (beta-LPH, Glu(145)-His(212)), gamma-lipotropin (gamma-LPH, Glu(145)- Ser(177)), beta-MSH (Asp(161)-Ser(177)), and beta-endorphin (beta-EP, Tyr(180)-His(212)). Catfish POMC protein does not contain a gamma-MSH region and most of the joining peptide and part of the gamma-LPH are deleted. Protein sequence alignment showed the highest similarity with the carp (Cyprinus carpio) POMC I (66.5%) and POMC II (67%), while the sea lamprey (Petromyzon marinus) POC (17.9%) and POM (18.8%) were the most divergent. The average similarity was 46.95% among the 44 POMC proteins from 36 different species analyzed. Compared to the POMC mRNA levels in the pituitary, the concentration of the POMC mRNA was 0.0594% in the anterior kidney and 0.0012-0.0045% in all the other tissues except in the skin where the lowest expression (0.0005%) was observed. Overall architecture of channel catfish POMC is highly similar to those from other teleosts.