SCHMITZ, R.S.; Univ. of Wisconsin Stevens Point: Ultrastructural characteristics of teleost fins.

Teleost fins are flexible two-dimensional sheets that undulate and bend to produce propulsive and stabilizing forces. In general all of the fins on the body of a teleost have a common trilaminar structure, consisting of two layers of epidermis sandwiching a layer of dermis that is reinforced with bony fin rays. When caudal fin of a cyprinid minnow is examined with the electron microscope, the epidermis consists of several layers of squamate, interdigitating keratinocytes. The cytoplasm of these cells is densely packed with intermediate filaments. The plasma membranes of these cells are tightly linked by continuous junctional complexes similar to desmosomes. The middle dermal layer is made up of highly ordered layers of collagen that span between the epidermal layers and between and around the fin rays. Conventional histological staining methods for elastin suggest that the dermis and the periostium of the lepidotrichia have an extensive elastic component. The bony matrix of the fin rays is amorphous adjacent to the periostial cells on the sides of the lepidotrichia segments, but highly ordered near the lepidotrichal joints. The ends of the lepidotrich segments are rounded and form a fibrous joint with adjacent segments. An examination of the microstructure of the caudal fin suggests that all of the tissues in the fin are designed to play a mechanical role in the production of undulatory propulsive swimming forces.