The first meiotic prophase was analyzed in both genders of Pacific white shrimp Litopenaeus vannamei. Progression through meiosis, from the formation of the synaptonemal complex to diplotene is described during molting stages. Most of the meiotic cells in both genders were observed at pachytene, recognized by complete synapsis of bivalents. In both genders, the zygotene, pachytene, and diplotene stages occurred at inter-molt, pre-molt, and post-molt stages in all individuals, which suggests that there is no relationship between molting and the first meiotic prophase. Sperm counts from the vas deferens and spermatophores support a continuous production of male gametes. The nature of the synaptonemal complex in gonad cells shows that each pair of homologous chromosomes synapses end to end, revealing a high chromatin density and a complex tangled arrangement in the nucleus. Both genders have 44 bivalents, of which around 40 have an o-ring configuration, and the rest have a v-shape, meaning that most bivalents present chiasmata at both ends, each representing two crossing-over events per bivalent per meiosis.
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Vol. 31 • No. 1