Temperature dependency of cupular mechanics and hair cell frequency selectivity in the fish canal lateral line organ

The mechanical frequency selectivity of the cupula located in the supraorbi tal lateral line canal and the frequency selectivity of the hair cells driv en by the cupula were measured simultaneously in vivo. Laser interferometry was used to measure cupular mechanics and extracellular receptor potential s were recorded to determine hair cell frequency selectivity. Results were obtained from two teleost fish species, the ruffe (Acerina cernua L.), a Eu ropean temperate zone freshwater fish, and the tropical African knife fish (Xenomystus nigri). In both species cupular displacement grows with increas ing frequency of canal fluid displacement, reaching a maximum at 115 Hz in the ruffe and at 460 Hz in the African knife fish. Cupular best frequencies were independent of temperature. Cut-off frequencies of hair cell frequenc y selectivity were found to depend on temperature with a Q(10) of 1.75, ran ging from 116 Hz (4 degreesC) to 290 Hz (20 degreesC), as established in th e ruffe. At normal habitat temperatures of the two fish species (ruffe, 4 d egreesC; African knife fish, 28 degreesC), this results in hair cell cut-of f frequencies that match the two different cupular best frequencies remarka bly well. This match suggests adjusted signal transfer in these two periphe ral stages of canal lateral line transduction.