Feeding behavior by parasitic phase lampreys, Ichthyomyzon unicuspis

Feeding behavior was initiated in juvenile and adult lampreys, Ichthyomyzon unicuspis, by attachment to goldfish or by injection of saline extracts of goldfish skin and muscle into the sucker cavity. Feeding was confirmed by the apparent swallowing of fish extract plus food dye by lampreys. Distinctive characteristics of feeding behavior included low frequency cycles, long duration (hours), variable biphasic pressure changes in the sucker cavity, and protraction of the tongue-like apicalis. In contrast, pumping behavior was used to move excess fluid from the sucker through the pharynx and out the gill pores; it was characterized by transient, high-frequency, monophasic suctions, simple retraction of the apicalis, and lack of swallowing.