Variable Gut Residence Time: Problems in Inferring Feeding Rate from Stomach Fullness of a Mysid Crustacean

Abstract

The gut residence time of the mysid crustacean Neomysis mercedis is extremely variable and is negatively correlated with ingestion rate. In two experiments in which mysids were fed copepod meals followed by continuous exposure to Daphnia, passage times varied from less than 1 to more than 13 h, and there were significant negative correlations of both copepod and daphnid passage times with the average feeding rate on Daphnia. In a third experiment starved mysids retained significant amounts of material in the stomach for more than 3 d. This dependence of evacuation rate on feeding activity may invalidate attempts to infer absolute or relative ingestion rate from the stomach fullness of field-caught animals.