Inducible nitric oxide synthase (iNOS) expression in cardiac tissues of fish reared under normal and elevated temperature. Immunofluorescence staining of iNOS (red color) and DAPI nuclear counterstain (white color) in cardiac tissues of fish reared for 56 days at normal temperature (14°C, upper panels) and high temperature (19°C, lower panels). At 14°C iNOS is expressed at low levels and in a few cells in the compact (A) and spongy (B) myocardium. At 19°C iNOS is expressed in a higher number of cells in the compact myocardium (C), and strong staining of individual myocytes is observed in the spongy myocardium (D). Panels A-D show one representative micrograph of three sections examined per fish from a total of three fish per temperature group. The 40 μm scale bar in panel A applies to all panels in the figure. E: Average number of positive cells ± SEM in spongy myocardium, calculated using a larger field of view (25× objective).