Induction of triploidy in spotted sand bass (Paralabrax maculatofasciatus Steindachner, 1868) by cold shock Juan Pablo Alca Ł ntar-Va Ł zquez, Silvie Dumas, Eleonora Puente-Carreo¤ n, Hugo Skyol Pliego-Corte¤ s & Renato Pen ì a Unidad Piloto de Maricultivo, Centro Interdisciplinario de Ciencias Marinas, Instituto Polite¤ cnico Nacional (CICIMAR-IPN). Av. IPN s/n, BCS, Me¤ xico Correspondence: S Dumas, Unidad Piloto de Maricultivo, Centro Interdisciplinario de Ciencias Marinas, Instituto Polite¤ cnico Nacional (CICIMAR-IPN). Av. IPN s/n, Col. Playa Palo de Santa Rita, La Paz, BCS 23090, Me¤ xico. E-mail: silviedumas@hotmail.com Abstract Conditions for the induction of triploidy with cold shock of fertilized eggs of the spotted sand bass Paralabrax maculatofasciatus (Steindachner) were in- vestigated. Di¡erent temperatures (12, 8 and 4 1C), timing of cold shock application (5, 10 and 15min after fertilization) and duration of the shock (5,10,15 and 20 min) were tested. Triploidy was determined using £ow cytometry at 12 h after larvae hatched. Triploids were produced only when the cold shock treatment was applied 5 min after fertilization. No signi¢cant di¡erence was observed in the percentage of triploidy between temperature and the shock dura- tion. At 8 and 4 1C, 100% triploidy was obtained at di¡erent durations of cold shock. Survival was signif- icantly lower at 12 or 4 1C than at 8 1C. No signi¢cant di¡erence was observed for shock duration at the temperature of 8 or 12 1C; however, at 4 1C, survival was signi¢cantly lower at longer durations. We re- commend induction of triploidy by applying cold shock at 8 1C for a duration of 15^20 min starting at 5 min after fertilization, in the spotted sand bass. Keywords: triploidy, spotted sand bass, cold shock Introduction In Mexico, no marine ¢sh species is raised from the hatchery through grow-out in sea cages. The spotted sand bass Paralabrax maculatofasciatus (Steindachner) has been identi¢ed as an economic resource (Matus- Nivo¤ n, Ram|¤ rez-Sevilla, Ortiz-Galindo, Mart|¤ nez-Pecero & Gonza Ł lez-Acosta 1989), found in Monterey Bay, California to Guerrero, Mexico. Throughout its range this species has a complex reproductive pattern. In Bah|¤ a de La Paz, in the southwestern part of the Gulf of California, it is considered a protogynic hermaph- rodite (Lluch-Cota 1995) with a reproductive season from January to May (Ocampo 2002). The spotted sand bass spawns spontaneously almost all throughout the year under adequate culturing conditions, ensuring a constant supply of larvae (Avile¤ s-Quevedo, Macgregor-Pardo, Rodr|¤guez- Ramos, Hirales, Huerta-Bello & Iizawa 1995). Some aspects of its cultivation have been described by our laboratory. Survival from hatching to the juvenile stage has been improved up to 10% (A Ł lvarez-Gonza Ł lez, Ortiz-Galindo, Dumas, Mart|¤ nez-D|¤ az, Herna Ł ndez- Ceballos, Grayeb del Alamo, Moreno-Legorreta, Pen ì a-Mart|¤ nez & Civera-Cerecedo 2000). Grow-out in cages (Grayeb del Alamo 2001) and nutrition trials (A Ł lvarez-Gonza Ł lez, Civera-Cerecedo, Ortiz-Galindo, Dumas, Moreno-Legorreta & Grayeb del Alamo 2001) have also been achieved. However, sexual maturation occurs before commercial size is reached. This is con- sidered a major problem because sexual maturation is accompanied by a decrease in growth rate and £esh quality and by an increase in susceptibility to diseases (Piferrer, Cal, A Ł lvarez-Bla Ł zquez, Sa Ł nchez & Mart|¤nez 2000; Felip, Piferrer, Zanuy, Carrillo 2001). A solution to this problem may be found in the production of triploid ¢sh that are functionally sterile from the odd number of chromosomes that cause disruption of meiosis in the gametes (Solar, Donaldson & Hunter 1984; Benfey 2001). Several shock methods are used to induce triploidy: temperature, hydrostatic pressure and chemicals. Temperature shock appears to be a suitable and e¡ective technique to induce triploidy because it does not require the use of chemicals or expensive equipment (Lemoine & Smith 1980; Arai & Wilkins1987). It can also be successfully Aquaculture Research, 2008, 39, 59^63 doi: 10.1111/j.1365-2109.2007.01869.x r 2007 The Authors Journal Compilation r 2007 Blackwell Publishing Ltd 59