Scanning electron microscopy of the channel catfish olfactory lamellae.

The olfactory lamellae of the channel catfish (Ictalurus punctatus) are composed of sensory and indifferent (non-sensory) epithelia organized into two distinct regions on both surfaces of each lamella. The smaller sensory region located adjacent to the midline raphe has fewer cilia per unit surface area than the indifferent epithelium and contains the olfactory neurons whose ciliated dendritic terminals occur at the epithelial surface. The indifferent epithelium, comprising the greater surface area of the olfactory lamella, is covered with a dense mat of non-sensory cilia. Fractured carbon dioxide critical point dried lamellar tissue revealed the underlying cellular structure. The lamellae are composed of two layers of epithelium enclosing a thin stromal layer. Olfactory receptors were observed in the fractured tissue only within the sensory epithelium.