Ž . Aquaculture 187 2000 73–84 www.elsevier.nlrlocateraqua-online Optimization of tetraploid induction in Pacific oysters, Crassostrea gigas, using first polar body as a natural indicator Benoit Eudeline a , Standish K. Allen Jr. b, ) , Ximing Guo c a Laboratoire de Biologie et Biotechnologies Marine, UniÕersite de Caen, Esplanade de la Paix, 14032 Caen Cedex, France b Virginia Institute of Marine Science, Aquaculture Genetics and Breeding Technology Center, College of William and Mary, Gloucester Point, VA 23062-1346, USA c Haskin Shellfish Research Laboratory, Rutgers UniÕersity, 6959 Miller AÕenue, Port Norris, NJ 08349, USA Received 15 April 1999; received in revised form 20 December 1999; accepted 22 December 1999 Abstract Tetraploid Crassostrea gigas were first successfully produced in 1993 by inhibiting the first Ž polar body of eggs from triploids that had been fertilized with sperm from diploids Guo and . Allen method . However, attempts to repeatedly produce high yields of tetraploids were inconsis- tent. Because of these uncertainties, we examined some of the fundamental aspects of tetraploid production in an attempt to optimize tetraploid induction using the Guo and Allen method. Ž . Varying the duration of the treatment to inhibit polar body 1 PB 1 of triploid eggs had clear Ž effects on ploidy of progeny. Short treatments 15–35 min after fertilization — about half the . Ž period of meiosis 1 in triploid eggs yielded tetraploid and heptaploid cells. Long treatments 7–43 . min — about three quarters of the period of meiosis I in triploid eggs yielded only heptaploid cells among the embryos. Tetraploid induction was most consistent when treatments were accomplished on eggs from individual triploid females rather than pooled from a number of females, and when treatments were metered according to biological landmarks. That is, eggs from Ž . individual triploids were fertilized and 0.5 mgrl cytochalasin B CB added after 10 min. A subsample of the fertilized eggs was kept aside untreated. When 50% of the untreated eggs Ž . showed PB 1 extrusion as judged by microscopic examination of dividing, untreated eggs , the CB treatment was discontinued. In eight treatments based on these ‘‘biological criteria,’’ ) Corresponding author. Ž . Ž . E-mail addresses: beudeline@aol.com B. Eudeline , ska@vims.edu S.K. Allen , xguo@hsrl.rutgers.edu Ž . X. Guo . 1 Current address: Whiskey Creek Oyster Farm, 3395 Bayshore Road, Tillamook, OR 97141, USA 0044-8486r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 00 00302-1