Temperature-dependent digestion handling time in juvenile cod and possibleconsequences for prey choice

The paper combines experimental work with modelling. The aim was to estimat e the temperature-dependent digestion handling time, which is defined as th e time taken to digest the whole prey or the whole stomach contents, and to examine potential consequences of prey digestibility on prey choice. A sur face-dependent digestion model that reflects the geometric shape of a pisci vore prey was applied to experimental data representing the weight of prey remaining undigested at various points in time from the time at which the p rey was first ingested. The fish used were juvenile cod fed different meal sizes of two-spotted goby Gobiusculus flavescens Fabricius at 4 temperature s. It is assumed that prey digestion is a surface process in which digestiv e enzymes attack progressively deeper into a prey of known size and shape s o that the average digestion rate would be proportional to prey radius. Thi s process is characterized by the digestion velocity d(s) (cm h(-1)) and th e digestion handling time. d(s) was estimated for various meal sizes and te mperatures. Next, these estimates were used to obtain a standardized temper ature-dependent function: d(s) = d(s0)[e((ln3.41/10)T)], Of which the stand ardized digestion velocity estimate at 0 degrees C, d(s) = 0.0026 cm h(-1). The d(s) relation expresses the digestion velocity over a 10-fold meal siz e increase for a temperature range within natural seasonal variation for th e cod. The digestion velocity d(s) was constant for a 10-fold difference in meal size within the temperature range. However, the digestion handling ti me increased with increasing meal size, but decreased with increasing tempe rature. It was demonstrated that predictions from a modified prey choice mo del which incorporates the effect of digestion differ from predictions from classical models which do not account for prey digestion.