The oral sucker of Gyrinocheilus aymonieri (Teleostei: Cypriniformes)

The sucker was studied in young and mature fish by light microscopy, histochemistry, transmission and scanning electron microscopy, X‐ray probe microanalysis, dissection, staining preparations of whole skeletons, and watching the animals in aquaria. The fleshy lips are supported by highly flexible, chondroid tissues, the structure and histochemistry of which differ substantially from those of cartilage. They allow the sucker to evert when the fish attaches to a stone or aquarium wall and are connected to the maxillae, premaxillae and dentaries. Lining the inside of the lips are two horny rasps, each with several regular rows of small hooks. The scraping blades of these hooks are keratinized and point towards the mouth. They increase the coefficient of friction for adhesion and enable the fish to feed on encrusting algae. Between the posterior rasp and the ‐anterior margin of the mandible are two invaginations of the lower lip that extend the sucker chamber beneath large hollows in the dentaries. The anterior margin itself contacts the outer surface of the maxillary oral valve when the mouth is closed, and isolates the sucker chamber from the rest of the buccal and pharyngeal cavities. Contrary to previous views, it is thought that a true vacuum is produced, and that attached fish spend long periods without taking water in through the mouth. The attachments of the principal jaw muscles are described and their role in sucker action discussed. There are similarities with the jaw mechanism of catostomids.