Sensitivity of Atlantic salmon eggs to mechanical shock during the first six hours after fertilization

Eggs from six domestic adult Atlantic salmon Salmo salar and six sea-run kelts (wild adults held over for a second spawning season) were tested at 0.5 to 6 h after fertilization for sensitivity to mechanical shock produced by dropping eggs from measured heights, Estimates of drop height and force causing 10% (lethal tolerance, LT90) and 25% (LT75) mortality were used to project egg sensitivity to handling while collecting, disinfecting, and transporting eggs to incubation facilities. Differences in LT90 and LT75 drop height or force were not significant among sample times up to 6 h postfertilization. The LT90 estimates of drop heights and force were 23.5-26.9 cm and 5,200-6,000 ergs for domestic eggs and 17.5-38.5 cm or 3,500-7,700 ergs for kelt eggs. The LT75 estimates of drop height and force were 46.1-60.3 cm and 10,200-13,400 ergs for domestic stock eggs and 43.7-65.1 cm and 8,800-13,100 ergs for kelt eggs. Variability in egg shock sensitivity among individual females was high and similar to differences in 24-h mortality observed in eggs transported for incubation. Our results show that a single dropping of eggs from a height of 17.5-38.5 cm could cause 10% egg mortality before eggs are incubated.