Electrophysiological responses of three chemosensory systems in the carp to pesticides

Responses of three chemical senses, olfaction, taste, and pit organ sense, to three pesticides were studied electrophysiologically in carp, Cyprinus carpio. Only olfaction was responsive to the three pesticides at behavioral avoidance levels, which were determined in a previous study. The olfactory thresholds for benthiocarb, isoprothiolane, and fenitrothion were 1.7 × 10−1 μg/l (4 log units lower concentration than 48-h LC50), 6.7 × 10−3 μg/l (6 log units lower than 48-h LC50), and 4.9 × 102 μg/l (1 log unit lower than 48-h LC50), respectively. There were two distinctive features in the olfactory response to pesticides. One is that these pesticides barely indicated the concentration dependency that is usually recognized in the olfactory response to a typical stimulant such as l-alanine or NaCl. Another is that these pesticides indicated a power spectrum with an overall increase in frequency ranges of less than 10.0 Hz, unlike l-alanine or NaCl, which show a marked peak ranging from 8.0 to 12.0 Hz. These findings suggest that there is a specific mechanism in the chemoreception for these pesticides.