Yolk-Sac Malformation in Pacific Salmon in Relation to Substrate, Temperature, and Water Velocity

Chum (Oncorhynchus keta), pink (O. gorbuscha), sockeye (O. nerka), and hybrid (pink × chinook) salmon alevins were susceptible to yolk-sac malformation when provided a smooth substrate as in standard hatchery incubators, at 12 C and a water velocity of 100 cm/hr. Chinook (O. tshawytscha) and coho (O. kisutch) alevins were not susceptible. In sockeye, malformations increased with increase in temperature from 8 to 12 and 14 C and, at 14 but not at 12 C, with increase in water velocity from 25 to 400 cm/hr. Replacement of the smooth substrate with a rough (gravel) substrate usually prevented the condition.