An Empirical Model of Gastric Evacuation Rates for Fish and an Analysis of Digestion in Piscivorous Brown Trout

The gastric evacuation rates of brown trout Salmo trutta (0.9–1.6 kg) feeding on fingerling rainbow trout Oncorhynchus mykiss (3.5–7.6 g) were measured in the laboratory at five temperatures (4.5, 9.0, 14.0, 19.0, and 22.5°C). Instantaneous gut evacuation rates (Re) increased exponentially with temperature (T): Re = 0.053·e0.073·T, r2 = 0.98; they varyied from 7%·h–1 at 4.5°C to 29%·h–1 at 22.5°C. Linear regressions described the relationship between time and qualitative measures of fish digestion, thus allowing investigators to determine how long an ingested fish would be identifiable at different temperatures. An analysis of published evacuation rates (N = 121) of 22 fish species indicated that both temperature and prey size (PS, g wet weight) significantly affected digestion rate (Re): Re = 0.049·e0.072·T– 0.060 loge(PS)R2 = 0.52. Predator size did not significantly affect rates of evacuation.