A SURFACE-DEPENDENT GASTRIC EVACUATION MODEL FOR FISH

A gastric evacuation curve expresses how fast prey disappear from the stomach, and empirical models are used generally for the relationship between weight of prey remaining (W-t) and time (t) after a meal. Unfo rtunately, empirical models are likely to have restricted applicabilit y because their parameters often represent limited biological mechanis ms. This paper develops a simple digestion model. The simplest form of the model has four parameters; the digestion velocity (expressing enz ymatic breakdown of prey), prey length, initial prey radius and the de nsity of the prey. Two more parameters are included in an extended ver sion; a time-delay before digestion starts and environmental temperatu re. The approach is based on the assumption that prey digestion is a s urface process in that digestive enzymes attack progressively deeper i nto a prey of known size and shape so that the average digestion rate is proportional to the prey radius r (m). This process is characterize d by the digestion velocity d(s) (m s(-1)). Unknown parameters are est imated with uncertainty using the maximum likelihood technique. Model evaluation using published data sets demonstrated that the new model i s flexible. Prey geometry is incorporated into the model and temperatu re effects upon gastric evacuation are linked directly to the digestio n velocity. (C) 1995 The Fisheries Society of the British Isles.