Evaluation of periodic and aperiodic otolith structure and somatic-otolith scaling for use in retrospective life history analysis of a tropical marine goby, Bathygobius coalitus

Abstract

Daily increment formation in sagittal otoliths, scaling between otolith and somatic growth, and the temporal link between settlement and formation of a settlement mark in otolith structure were evaluated for their use in reconstructing aspects of the early life history of the basalt goby Bathygobius coalitus. Formation of daily increments was validated in sagittae of fish ranging in life history stage from new recruits to sexually differentiated males and females. Total length (TL) was proportional to other measures of body length, width, and depth, and linearly proportional to sagitta radius for fish between 8 and 40 mm TL. Somatic-otolith scaling became more curvilinear in larger fish due to declining growth rate of otoliths relative to TL, especially in fish collected during warmer sea surface temperatures. For fish 8 to 40 mm TL, somatic-otolith scaling was not affected by differential somatic growth rates nor by seasonal water temperature. A settlement mark, clearly identifiable as a distinct and abrupt shift in optical focal plane, contrast, and width of daily increments, was verified to coincide with settlement. Wider post-settlement increments abruptly followed narrower pre-settlement increments across the settlement mark. These results support the use of daily increments, somatic-otolith scaling, and a settlement mark for reconstruction of hatch and settlement dates, mean daily pre- and post-settlement growth rates, size and age at settlement, and post-settlement size-at-age histories for the basalt goby.