State of the heart: Anatomical annotation and assessment of morphological cardiac variation in Atlantic salmon (Salmo salar L.)

Abstract

Farmed Atlantic salmon suffer from deviating cardiac morphology, likely compromising fish health and robustness. To mitigate the potentially devastating consequences of morphological deviations of the heart, the cause and consequences of these abnormalities need to be elucidated. This endeavour is, however, complicated by several obstacles. First, a detailed nomenclature of gross anatomical structures of the pyramidal fish heart is needed to develop standardized descriptions of morphological deviations. Second, standardized methods and scoring systems for quantitative and qualitative descriptions of cardiac anatomy are lacking. Lastly, the normal morphological development of the heart through the life cycle of wild specimens has not been described, making it challenging to identify deviating morphology at different life stages of farmed salmon. Here, we develop a nomenclature for the exterior of a pyramidal teleost heart, using the Atlantic salmon heart as a model. Further, we have unified and described the most common quantitative methods used for measuring heart morphology and developed a qualitative methodology to detect morphological abnormalities not identified by the quantitative methods. We describe the methodologies' applicability and assess the qualitative method's robustness. Using quantitative measures, heart morphology in the wild and farmed salmon is compared throughout their life cycles. Further, we show that the qualitative method is superior to the quantitative method in detecting traits more prevalent in deceased fish after exposure to stressful routine field treatments, illustrating the complementary nature of these two methods.