MORPHOLOGICAL AND PHYSIOLOGICAL-STUDIES ON THE OLFACTORY ORGAN OF THE STRIPED EEL CATFISH, PLOTOSUS-LINEATUS

The olfactory organ of the striped eel catfish, Plotosus lineatus (Thunberg), obtained off Kyushu Island, Japan, was examined both morphologically and electrophysiologically. The olfactory organ of P. lineatus differs from that of most other catfishes, possessing a small olfactory rosette containing only relatively few lamellae, a well-developed olfactory ventilation sac used as the primary means of propelling water through the olfactory chamber, and olfactory sensory epithelia lying in discrete patches rather than continuously distributed across the lamellae. Although morphological differences in the olfactory organ between P. lineatus and other catfishes are significant, the physiological characteristics are remarkably similar. Response thresholds for amino acids (L-cysteine and L-glutamine) were ca. 10(-9) M, and the relative effectiveness of 16 amino-acid stimuli differed little from those reported for other catfishes.