Feeding history influences otolith shape in tropical fish

The influence of feeding history on otolith shape and symmetry was examined in juveniles of 2 species of coral reef fish, Amphiprion akindynos and Pomacentrus amboinensis. Fast Fourier analysis was used to describe the shape of otoliths of fish from a variety of experimental feeding treatments, ranging from starvation, through pulse feeding, to feeding ad libitum. The resulting harmonics from both the left and right otoliths of each individual fish were used in a multivariate analysis to investigate shape differences among feeding treatments in the 2 species. When left and right otoliths were analysed separately, no significant differences between feeding treatments were revealed for either species. In contrast, when left and right otoliths from individuals were analysed together, clear separations in feeding groups were observed in both species. Differences among feeding treatments were largely due to differences in the finer details of the otolith shape, represented by the middle level harmonics. Fish that had been starved had significantly different otolith shapes than fish from all other treatments. Differences in otolith shape could not simply be attributed to differences in fish size or age among treatments. We conclude that differences in otolith shape are influenced by recent feeding history, but processes that influence otolith shape are complex and most likely species-specific. This study presents new evidence that otolith shape of tropical fish may directly reflect body condition of individuals regardless of fish size and age.