Laterality defect of the heart in non-teleost fish
Dextrocardia is a rare congenital malformation in humans in which most of the heart mass is positioned in the right hemithorax rather than on the left. The heart itself may be normal and dextrocardia is sometimes diagnosed during non-related explorations. A few reports have documented atypical positions of the cardiac chambers in farmed teleost fish. Here, we report the casual finding of a left-right mirrored heart ventricle in a 85 cm long spiny dogfish (Squalus acanthias) that was caught in the wild. Macroscopic observations showed an outflow tract originating from the left side of the ventricular mass, rather than from the right. Internal inspection revealed the normal structures, including a looped cavity on the inner curvature of which was a large trabeculation, or the bulboventricular fold. MRI data acquired at 0.7 mm isotropic resolution and subsequent 3D-modeling revealed the atrioventricular canal was to the right of the bulboventricular fold, rather than on the left. The atrium and sinus venosus had the normal midline position and gross shape. Spurred by finding of the left-right mirrored shark ventricle, we revisit our previously published material on farmed Adriatic sturgeon (Acipenser naccarii), a non-teleost bony fish. We found several alevins with inverted (L-loop) hearts, amounting to an approximate incidence of 1-2 %. Additionally, an adult sturgeon measuring 90 cm in length showed abnormal topology of the cardiac chambers, but normal position of the abdominal organs. In conclusion, left-right mirrored hearts, a setting that resembles human dextrocardia, can occur in both farmed and wild non-teleost fish.