Factors affecting gastric evacuation in cod, Gadus morhua L., fed single‐meals of natural prey

Abstract

Functional relationships were derived in order to describe the effects of fish weight (262–2066 g), temperature (1–14° C), prey size and ration size (0.4–8.4% body weight) on gastric evacuation in cod fed four natural prey types. Interindividual (unexplained) differences among voluntary fed cod were relatively large. Power functions were appropriate for describing the effects of fish weight and ration size on the half‐time of evacuation. Effects of meal and/or prey size appeared to counterbalance the effects of cod size. It is suggested that when cod of different sizes are fed fixed proportions of their body weight evacuation time is constant and independent of body size. There was found to be an exponential relationship between temperature and gastric evacuation time but, observations made at similar temperatures at different times of the year suggested that seasonal effects were of minor importance.