The reproductive biology and estuarine movements of the gizzard shad, Nematalosa vlaminghi (Munro)

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Abstract
The microscopic development of the egg of the Perth herring, Nematalosa vlaminghi, has been related to the gross changes observed in the ovary. The patterns of change in the diameter of the oocyte, oocyte nucleus, yolk vesicles and yolk granules and the thickness of the theca, granulosa and zona radiata have been quantified. Three modes were present in frequency histograms of the diameter of oocytes in sexually‐mature females, two of which corresponded to opaque and hyaline yolked‐oocytes. The mean number of hyaline oocytes was 20430, which represented 35% of the mean number of all yolked oocytes (57610). Seasonal trends in gonadosomatic indices, together with the changes in the macroscopic and microscopic condition of the ovaries, demonstrated that spawning activity reached a peak in December‐January. The place of capture of mature animals and 0+ recruits showed that breeding occurred near the top end of the upper estuary. During the ensuing weeks, the young fish dispersed throughout the upper and middle estuary while the older fish moved out to sea.