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Fig. 15. Danio rerio: (A) Upper panel: The zygotic vas::egfp commences to highly express after
16 dpf in females but males of types I, II and III, which began to faintly express, progressively
decrease the expression at different dpf (day post-fertilization). The increasing fl uorescence
intensity suggests the increasing oocyte number and growth of ovarian lumen and shape. In
contrast the decreasing fl uorescence indicates the degeneration of oocytes and transformation
of ovary into testis. (B) Lower panel: A model for gonad differentiation showing high levels of
variation in the intensity, onset and duration of gonad transformation (from Wang et al 2007.
The timing and extent of the juvenile ovary phase are highly variable during zebrafi sh testis
differentiation. J Fish Biol, 70A: 33-44, reproduced by permission of The Fisheries Society of
the British Isles/John Wiley & Sons Ltd)
Color image of this figure appears in the color plate section at the end of the topic.
(Fig. 15). Considering the intensity of expression, shape of gonad and
number of oocytes, the transforming presumptive males are grouped into
three types (Table 15). At least 42% of presumptive males seem to have
completed male differentiation at the 32 dph.
Sex differentiation in juvenile/adult zebrafi sh is mediated by genetic
signals from autosomal genes. Expression profi les reported by Jorgensen et
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