Physiological response of juvenile coho salmon (Oncorhynchus kisutch) and rainbow trout (Salmo gairdneri) to handling and crowding stress in intensive fish culture

Moving 4–5-in. coho salmon (Oncorhynchus kisutch) held in soft (20 ppm CaCO₃) water from the relatively light loading density of 0.5 lb/ft³ to 1, 2, or 4 lb/ft³ (density index, DI = 0.1, 0.2, 0.4, 0.8) caused significant stress as indicated by loss of feeding behavior, but only minimal physiological disturbances, as indicated by lack of hyperglycemia or hypochloremia. However, moving them to 6 or 12 lb/ft³ (DI = 1.2, 2.4) caused significant physiological stress which required at least a week for recovery. Smolting coho salmon were physiologically stressed by population densities of 1 lb/ft³ or more and a subclinical corynebacterial kidney infection was activated. Rainbow trout (Salmo gairdneri) (4–5 in.) were physiologically stressed when moved and held at 1 lb/ft³ or more but retained normal feeding behavior. This indicates that handling and crowding stress will be minimized in softwater areas if densities in fish distribution trucks or in ponds or raceways during disease treatments are held to 0.1–0.5 lb/gal.