Zoological Studies

The Relative Distribution of Otoliths as a Means of Larval Fish Identification

Li Shu Chen and Hong Young Yan (2002) A recently developed auditory brainstem response (ABR) protocol has indicated that acoustically evoked brainwaves in fishes are species-specific. These brainwaves reflect the spatial distribution of auditory nuclei and the 3 auditory end organs along the ascending auditory neuronal pathways. Species-specific brainwaves suggest the hypothesis that the distribution of otoliths, which are closely coupled with sensory hair cells whose evoked response forms the 1st wave of the ABR, should also be species-specific. Eight species of marine fish larvae (belonging to 8 genera and 4 families) collected from Taiwan and Texas, USA were cleared in trypsin and examined microscopically with double polarization filters. Three indices (inter-utricular ratio, IUR; inter-saccular ratio, ISR; and inter-lagena ratio, ILR) were developed to measure the ratio of inter-otolithic to inter-orbital distances. IUR and ISR succeeded in separating species, but ILR was not as useful because of late development of the lagena. This study supports the hypothesis that the distribution of otoliths in fish larvae differs among species.