The epidermis of fish is covered with a layer of mucus which contributes to the defence of the species against parasites, bacteria and fungi. We have previously extracted glycoproteins from various mucus samples from fish and have shown that they have pore-forming activities well-correlated with strong antibacterial properties (Ebran et al. Biochim. Biophys. Acta (2000) 1467, 271-280). This study focuses on the 65 kDa glycoprotein Tr65 from the trout Onchorhynchus mykiss. Enzymatic digestion of Tr65 yielded a fragment pattern with strong homology to that of trout type II cytokeratin. Sequence analysis of the cDNA clone obtained by PCR confirmed this homology. We thus constructed a plasmid to overproduce recombinant Tr65. We extracted and purified this recombinant Tr65, using it for multi-channel and single-channel experiments in azolectin bilayers. Our results with recombinant Tr65 confirmed the pore-forming properties already shown with native antibacterial Tr65. These findings offer new insight into the function of keratin proteins present in various mucosal surfaces of animals and human beings.