Morphological development and microstructure of sagittal otolith of large yellow croaker, Larimichthys crocea during larval and early juvenile stages

Abstract

We documented the morphological development and microstructure of the sagittal otolith during the larval and early juvenile stages(between hatch and 78 d after hatch) of large yellow croaker(Larimichthys crocea).We observed daily periodicity in growth increment formation in the sagittal otoliths.The first daily increment was formed 2 days after hatching(dah),corresponding to the time of first feeding.The sagittas were round in shape during the yolk-sac larval and pre-flexion larval stages,subsequently becoming elongated on the long axis during the flexion larval stage.Following this,the sagitta became ellipsoid in shape during the post-flexion larval stage.During the early juvenile stage,the first secondary primordium began to form between 29?39 dah(32±0.39),cor-responding to the timing of metamorphosis from larvae to juvenile.The number of secondary primordium ranged from 5 to 7 in 47–??78-day-old juveniles,and the secondary growth zone(SGZ) surrounding the first growth zone(FGZ) formed an "enclosed structure".During this stage,the sagittas were nearly peltate in shape.The radius(R) of the sagitta was significantly and linearly related to standard length(LS) for all individuals(R =–155.8+39.1 LS)(n=211,P0.001).The growth rates during the larvae stage(b),calculated based on the width of the daily incre-ment on the sagitta of juveniles,were significantly and linearly related to the time of formation of the first secon-dary primordium(tSP1)(b =38.6–161.9tSP1)(n=42,P0.01).This suggests that the secondary primordium was formed much earlier and metamorphosis was more rapid in faster growing larvae.In summary,the pattern of early life history growth and development of large yellow croaker can be back-calculated based on sagitta size,mor-phology,and microstructure.Our results provide a theoretical basis for measuring early growth and development and documenting recruitment of large yellow croaker in the field.