Bacterial Populations during Inland Fall Chinook Salmon Egg Culture in Vertical-Flow Tray Incubators

Abstract

Bacterial samples were collected from water flowing through vertically stacked trays during the incubation of eggs of inland fall chinook salmon Oncorhynchus tshawytscha. Bacteria numbers gradually increased until the eyed stage of egg development and then decreased after removal of dead eggs. Bacterial abundance peaked during hatching and declined thereafter. Throughout incubation, bacterial abundance increased from the top to the bottom of the stack. Mechanical picking of dead eggs at the eyed stage led to a decrease in bacteria numbers. Removal of dead eggs and fry by hand picking resulted in a temporary increase in bacteria population, with a return to prepicking levels after 30 min. Egg survival at the eyed stage of development was inversely related to tray position, decreasing from top to bottom of the incubation stack. Survival from the eyed stage to fry swim-up was not affected by tray location. If high egg mortality is anticipated, hatchery managers may want to consider changes in egg rearing densities and incubation water flows to alleviate any potential negative impacts caused by bacterial populations.