The influence of egg incubation and rearing temperature on heart morphology and function in farmed Atlantic salmon (Salmo salar)

Abnormal heart morphology is linked to increased mortality in farmed Atlantic salmon at sea. While water temperature is known to affect cardiac morphology, the role of egg incubation temperature remains poorly investigated. We examined whether egg incubation temperature affects cardiovascular health and development from hatching to smoltification. In addition, the cardiac effects of simulated winter-spring regime (low temperature and variated photoperiod, 1+ smolts) was compared with an accelerated smolt protocol (continuous high temperature and 24:0 light; 0+ smolts). Atlantic salmon eggs were incubated at temperatures ranging from 1.3 to 7.6 °C, and cardiac morphology and function were assessed before start-feeding (alevins) and immediately before sea transfer. Accumulated hatchery-mortality increased in a temperature-dependent manner. Alevins from warmer incubation temperatures had reduced body size and rounder, relatively smaller ventricles with higher heart rates. In addition, this group exhibited scoliosis, anemia, and more frequent cardiac morphological deviations. Smolts from eggs incubated at ∼5 °C had larger atria, stroke volume and cardiac output than both colder (∼2 °C) and warmer (∼8 °C) temperature regimes suggesting more favorable cardiac morphology and function. Smolts with a prolonged winter-period maintained more wild-like morphology with more pyramidal ventricles, while 0+ smolts had larger but rounder, less symmetrical ventricles that showed signs of myocardial hypertrophy. Taken together, our results suggest that intermediate egg incubation temperatures, combined with a prolonged period in cold freshwater prior to sea transfer, promotes more wild-like cardiac morphology and performance in farmed Atlantic salmon.