Figure 4. Distinct changes in spongy and compact myocardium in juvenile pink salmon following embryonic oil exposure.

A subset of hearts from fish 8 months post-exposure for which dimensions were measured in Fig. 3 were sectioned and stained with hematoxylin/eosin. (A) Sections were selected that showed the atrium (a) and ventricle (v), with a clear midline plane through the bulbus arteriosus (ba) and ventricular-bulbar valve. (B) Cardiomyocyte diameters, (C), numbers of cardiomyocyte nuclei and (D) thickness of the compact myocardium were measured in the indicated areas (A, red squares, black circles, and blue squares respectively). (E) Levels of mRNA for atrial (nppa) and B-type natriuretic peptide (nppb) in pink salmon hearts normalized to the reference gene ef1α. All data are mean ± s.e.m. ANOVA showed significance for effect of oil exposure for compact myocardium thickness (P = 0.02) and density of nuclei (P < 0.0001). Asterisks indicate treatments that differed significantly from controls (Dunnett’s post-hoc test, α = 0.05).