Quantitative scanning electron microscopy of solitary chemoreceptor cells in cyprinids and other teleosts

Abstract

Solitary chemosensory cells (SCC) occur in the epidermis of many lower, aquatic vertebrates. By scanning electron microscopy, SCC apices were counted and density distributions estimated along various transects at the head and body of 12 species of teleost fishes, 7 cyprinids, 2 perciforms, 2 catfish and 1 characinid. In contrast to taste buds (TB), the distribution of SCCs is relatively even, with slightly higher densities at the forehead and along the dorsal trunk. In most species 1000 to 1500 SCC apices per mm2 of skin were counted. Considerably higher densities occur in halos around free neuromasts. Depending on fish size and apex density, the epidermis of individuals may contain millions of SCCs. SCCs are considerably more abundant in individual fish than TB sensory cells. Highest average SCC densities (2000–4000 per mm2) were found in the cyprinids, roach, nase, chub and bream. Lowest densities (250 per mm2) occurred in the neon tetra. No correlations could be found between SCC densities and TB densities or relative size of the brain stem facial lobe, supporting the view of different functions and biological roles of the SCC and the TB systems. Whether teleost SCCs generally respond to mucoid substances, as in the case of the rocklings, remains an open question.