ABSTRACT
Five basic tissues, epithelial tissue, connective tissue, muscular tissue, skeletal tissue, and nervous tissue, are demonstrated in fish. Epithelia are classified into two types according to the number of the layers, first, simple: one cell layer thick, and, second, stratified: many layers of cells. Epithelia are also classified according to the shape of the cells into (1) squamous: flat cells with a flat nucleus; (2) cuboidal: square in shape with a rounded nucleus; (3) columnar: rectangular with oval basally located nucleus; and (4) pseudostratified: two types of cells are demonstrated with nuclei arranged at different levels. Epithelia are further classified by its apical surface specializations into microvilli, microridges, and cilia. Epithelia also form the essential parts of the glands. Taste buds populate in the stratified epithelium of the integument and of the buccopharyngeal to the esophageal cavity. The connective tissue serves as connecting and filling tissues, lying beneath the epithelial tissues of the skin and digestive tract. Each type of connective tissue consists of cells scattered in an extracellular matrix consisting of fibers in an amorphous ground substance. Collagenous, reticular, and elastic fibers occur in connective tissue. The various cell types of connective tissues are divided into two groups: one, the population of fixed cells, which includes fibroblasts and adipose cells, and, another, the population of wandering or free cells whose presence primarily depends on the functional state of the tissue.
As in other vertebrates, five basic tissues, epithelial tissue, connective tissue, skeletal tissue, muscular tissue, and nervous tissue, are demonstrated in fish.
