Some morphological and behavioural adaptations of pile perch (Rhacochilus vacca) feeding on mussels (Mytilus edulis)

Abstract

Pile perch were found to feed readily on single whole mussels. These were crunched by the massive pharyngeal teeth of the perch and swallowed completely without shell ejection. In the gut a mucous coating enveloped the fragmented shells protecting the mucosa from injury. The mucous envelope dissolved rapidly following defecation. X-rays of the intestine and sonic recording by hydrophone of the crunching sounds were used to follow digestion and trace the feeding frequency when browsing on a colony of mussels. At 10 °C, after 1 h of intensive feeding, the mussels took from 1 to 4 days to be completely digested; the shell fragments were unaffected by digestion. On a fixed photoperiod, feeding activity was confined to daylight hours except some exploratory browsing which occurred immediately prior to lights coming on.