MEPS 228:205-211 (2002)  -  doi:10.3354/meps228205

ABSTRACT: A metamorphosis check (MC) is a protein-rich, slow growth zone in fish otoliths. It has been proposed that deposition of this structure occurs during life history transitions, usually during migration from marine to freshwater habitats. To clarify MC deposition in relation to habitat shift and ontogenetic change of the amphidromous goby Sicyopterus japonicus, otolith microstructure, microchemistry (Sr/Ca) and morphological changes were examined across ontogenetic stages (larval, postlarval, juvenile, and adult) and environments (estuarine and a freshwater stream). The otolith Sr/Ca ratios were higher in the estuary than in the stream environment. The MC was not found in otoliths until the fish metamorphosed from larvae to juveniles, indicating that it was deposited at the juvenile stage after migration from seawater to the freshwater habitat. The deposition of the check was concomitant with a change in head morphology associated with a transition in feeding behavior. Metamorphosis checks in otoliths provide further evidence of the usefulness of daily growth increments in reconstructing the early life history of diadromous fishes.

KEY WORDS: Amphidromous fishes · Goby · Metamorphosis check · Otolith · Sr/Ca ratios · Morphology