The feeding mechanisms in plankton eaters

The feeding mechanisms of 15 whitefish Coregonus lavaretus (Lin.) from the Gulf of Bothnia near Holmsund were studied. The fishes were very susceptible to infection. Different preparation and anaesthesia methods were tested. Careful dissections revealed a vestigial epibranchial organ extending from the dorsal part of the fifth gill slit. It is suggested that this little sac receives and accumulates plankton organisms which may then be carried to the oesophagus via a special pharynx groove. In this way the whitefish could effectively use small plankton as a complementary food source to larger food particles.