Effect of Thermal Shock on Vulnerability of Juvenile Salmonids to Predation

Abstract

Thermally shocked juvenile rainbow trout and chinook salmon were selectively preyed upon by larger trout in the laboratory when exposure times to elevated temperatures exceeded a minimum duration. This duration was 10% (chinook) and 20% (rainbow) of the exposure duration that caused obvious loss of equilibrium (complete body inversion) of half a test population at that temperature. Longer exposures increased vulnerability to predation relative to controls almost exponentially. Shorter exposures made shocked fish less susceptible to predation. Shocked fish showed some recovery from heat effects when returned to the initial holding temperature for [Formula: see text] or 1 hr prior to predation. Susceptibility of rainbows to predation (relative to controls) appears to follow the time- and temperature-dependant response pattern previously shown by others for death and visible equilibrium loss. Selective predation began at exposures about 10% of the median death time in the range 26 to 30 C.