The ventral adhesive disc of the clingfish Gobiesox maeandricus: integumental structure and adhesive mechanisms

Abstract

Light microscopy and scanning and transmission electron microscopy of the ventral adhesive disc of the northern clingfish, Gobiesox maeandricus, demonstrate that two distinct types of epidermis are present on the disc surface. Most of the disc is covered with cuboidal epithelium in which four cell types can be distinguished: acidophil cells, mucous cells, epithelial cells, and "alarm substance" cells. The surfaces of the epithelial cells feature whorled microridges typical of teleost epidermis. Near the margin of the disc, on the lateral fin rays, and in discrete raised patches inside the disc are papillae of stratified columnar epithelium. The surface cells of these papillae are microvillous and secrete a noncellular cuticle which is firmly anchored to the microvillous surface of the papillae. The cuticle is not adhesive. It contains keratin-like proteins but no mucins or mucoproteins are demonstrable histochemically. Connective tissue layers and muscle underlying the epidermis of the disc are arranged to provide structural integrity and shock absorption while allowing some flexibility to the disc and papillae. The adhesive force generated by the disc was demonstrated using a pressure transducer. Negative pressure decays over time and is periodically renewed by the fish. Thus suction is largely maintained passively and the disc's seal is subject to some leakage. The fish can also actively apply suction pressure when agitated but fatigues and cannot sustain high negative pressures for long. The epidermal papillae, coupled with the fish's ability to flex the disc, represent an additional gripping mechanism for irregular surfaces. The papillary surface cuticle apparently acts as an abrasion-resistant, frictional surface.