Validation of otolith daily increments in the amphidromous goby Sicyopterus japonicus

To determine the periodicity of growth increment deposition in the otoliths of newly recruited larvae of the amphidromous goby Sicyopterus japonicus, an otolith validation experiment was performed. Larval gobies collected at the river mouth of the Ota River, Wakayama, Japan were immersed in an alizarin complexone (ALC) solution to mark the timing in their otoliths. After being held under natural light conditions for 15 days, they were treated with ALC again to make the second time mark. The number of growth increments between two ALC marks in the otoliths was 14.1 on average, which roughly coincided with the number of days between two ALC treatments. This experiment validated the daily periodicity of otolith growth increment deposition in S. japonicus showing that the otolith increments of the species can be used for age determination with daily precision.