Otolith microstructure and growth patterns during the early life history of lanternfishes (family Myctophidae)

Abstract

The microstructure of the central part of the sagittal otoliths of 55 myctophid species belonging to 27 genera of lanternfishes was compared by means of light and scanning electron microscopy. Multiple primordia were found in the nuclei of all otoliths. In most species and genera a symmetrical pattern of accessory primordia (AP) was observed: they were located along the same growth increment, which indicates simultaneous formation. A clustered pattern of AP was found only in species belonging to the tribe Gymnoscopelini: AP occurred at several growth increments, which indicates that they developed sequentially. The growth increments formed after the formation of clustered AP revealed a sectorial otolith structure, i.e., growth increments were not continuous but separated by radial discontinuities. The pattern and time of formation of AP were found to influence the relationship between otolith diameter and fish length in the Myctophidae. The formation of numerous AP concurrently with transformation of the larva led to a dissociation of fish growth from otolith growth. When AP appeared simultaneously but before transformation, the allometric relationship between otolith size and fish length was not disrupted by this process. Sequential formation of AP considerably before transformation, which occurred only in the Gymnoscopelini, led to an isometric relationship between fish size and otolith size. The potential importance of the AP pattern as a distinguishing character for myctophid larvae is considered to be greatest in the Gymnoscopelini, as these growth centers, in the form of external protrusions, were evident over a wide range of sizes from small larvae to early juveniles.