Adhesion by Paired Pectoral and Pelvic Fins in a Mountain-Stream Catfish, Pseudocheneis sulcatus (Sisoridae)

We describe the adhesive nature of the pectoral and pelvic fins in the catfish Pseudocheneis sulcatus, as examined by scanning electron microscopy. The outer rays of these fins are modified into structures that bear prominent transverse ridges and grooves. The outer epidermal cells of the ridges are thrown into elongated spines. Mucous pores (openings of mucous glands) are frequently present (100m apart) in the epidermis of the ridges and show entangled mucus droplets. In the pectoral fins, they are present towards the contour areas of the outer rays, but they are absent in the pelvic fins. In the latter, mucous pores are present near the base of the ridges (distal to the inner rays). Spines as well as mucous pores are absent in the cells that line the groove between two adjacent ridges. We suggest that in this species adhesion is effected by suction pressure generated by the musculature attached to the grooves and ridges, and that mucus and the spines aid in this process.