Twin meiosis 2 spindles form after suppression of polar body 1 formation in oocytes of the marine shrimp Sicyonia ingentis

The production of triploid shellfish has proven beneficial to the aquaculture industry since triploid organisms have reduced gonadal development, resulting in improved product quality and growth characteristics (1). Triploidization has been achieved for several molluscan species (2, 3, 4, 5, 6). In contrast, little is known about the effects of ploidy manipulation in decapod crustaceans. Triploidy has been induced in Penaeus chinensis and other penaeid shrimp using heat shock or cold shock, cytochalasin B, and 6-dimethylaminopurine (7, 8, 9, 10, 11). Triploidy was induced by suppression of polar body 2 in the shrimp Litopenaeus vannemei using cold shock, but resulted in poor survival for unknown reasons (11). One difficulty of ploidy manipulation in L. vannemei is the rapid sequence of meiotic events, since the polar bodies are produced at 8 and 15 min post-spawning at 28°C (12). In addition, the actual behavior of chromosomes and spindles was not addressed. Here I report that in the penaeoidean shrimp Sicyonia ingentis, inhibition of polar body 2 resulted in embryos that failed to undergo embryonic cleavage, while inhibition of polar body 1 produced oocytes with "twin" meiosis 2 spindles followed by the simultaneous formation of two "second" polar bodies.