Abstract
ABSTRACT Saccular otoliths are hearing and balance structures in teleost fish and usually consist of the aragonite form of calcium carbonate but may contain varying amounts of the vaterite polymorph in abnormal cases. Environmental impacts, nutritional problems, pollution, stress, and changes in water parameters, or a combination of these factors, may cause deformities in saccular otoliths. In this study, we examined the morphologies and calcium carbonate polymorphs within abnormal and normal saccular otoliths in the anchovies Engraulis australis, retrieved from regurgitated stomach contents of the Australasian gannet Morus serrator, Hauraki Gulf, New Zealand. Scanning electron microscopy (SEM) and Raman microscopy revealed several prominences in numerous areas on the surfaces of abnormal otoliths. This is the first study to report on the morphology and compositional differences in abnormal otoliths retrieved from the food of a piscivorous bird in New Zealand. Abnormalities in the structure and composition of otoliths may impact balance and hearing functions in fish and have implications on their fitness. Further studies should explore whether such fish are preferentially targeted by their avian predators.
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