INVESTIGATING FACTORS CONTRIBUTING TO REDUCED EMBRYO SURVIVAL IN FARM-RAISED ATLANTIC SALMON, Salmo salar L.  

Embryo mortality of Atlantic salmon, Salmo salar, has been increasing for more than a decade in the State of Maine, a leading producer of this species in the United States.  Increasing embryo mortality not only creates a financial bottleneck for farms, but also prevents the sale of surplus eggs as an additional source of revenue.  Blood and egg samples were collected at three Maine Atlantic salmon farms from female broodstock at the time of spawning over a two year period. Correlative factors for reduced embryo survival were investigated by measuring egg and maternal plasma concentrations of 17β-estradiol (E2), 11-ketotestosterone (11-KT), testosterone and calcium, as well as maternal hepatic ethoxyresorufin-O-deethylase (EROD) activity and fork length.  Significant positive correlations were found between maternal plasma concentrations of E2 and 11-KT and embryo survival (Figure 1).  Interestingly, there was no correlation with egg concentrations of sex steroids and embryo survival, suggesting that embryo mortality does not likely rest with the maternal deposition of sex steroids into the egg, but with another hormone regulated process related to egg assembly, ovulation or post-ovulatory aging.