Effectofnumberofspawnsontheresultingspawn quality of 1-year-old pond-reared Penaeus vannamei (Boone) broodstock Elena Palacios & Ilie S Racotta Divisio Ân de Biologõ Âa Marina, Centro de Investigaciones Biolo Âgicas del Noroeste, Apdo. Postal 128, La Paz, Baja California Sur 23000, Me Âxico Correspondence: E Palacios, Divisio  n de Biologõ Âa Marina, Centro de Investigaciones Biolo  gicas del Noroeste, Apdo. Postal 128, La Paz, Baja California Sur 23000, Me Âxico. E-mail: epalacio@cibnor.mx Abstract For production of shrimp larvae in a commercial hatchery, multiple spawning of females is highly desirable, provided spawn quality is not affected. Using biochemical and production approaches, 349 females were individually followed, and 69 spawns were sampled over a 3-month period. The quantity of eggs and nauplii per spawn was greater in females with multiple spawns. Several indicators of spawn quality, such as fertilization and hatching rates, per cent of viable spawns, and morphometric character- istics of eggs and nauplii were not affected by consecutive spawns. Analyses of egg and nauplii biochemical composition indicate that adequate transfer of nutrients to eggs is not compromised with successive rematurations and spawnings. Strategies that focus on the selection of shrimp with multiple spawning capacities could be a prom- ising approach to increasing larvae production. Keywords: biochemical composition, consecutive spawns, egg quality, reproduction, shrimp Introduction In commercial hatcheries, the proportion of females who contribute to the overall nauplii production is small. This condition has led to the suggestion that selective replacement of non-productive females be conducted during the production period (McGovern 1988; Palacios, Racotta & APSA 1999). In addition, selection of high-performance spawners through several generations could help improve nauplii pro- duction (Bray, Lawrence & Lester 1990; Wyban & Sweeney 1991; Palacios, Racotta & APSA 1999). Females that spawn frequently are more desirable, with the condition that offspring quality is not affected. However, Simon (1982) has reported that after a few months in a hatchery cycle, eyestalk- ablated females produce lower-quality eggs and larvae, leading to replacement of all the broodstock. Decline in spawn quality has been associated with consecutive spawns (Emmerson 1980; Marsden, McGuren, Hansford & Burke 1997) or with time in production after eyestalk ablation (Simon 1982; Palacios, Pe Ârez-Rostro, Ramõ Ârez, Ibarra & Racotta 1999). Inferior quality of spawn compromises the use of spawners that have produced several spawns, and limits the ability to establish a strategy for selecting females with such characteristics. How- ever, in previous investigations, no significant effect on the biochemical composition and cytological characteristics of the ovary in relation to consecu- tive spawns was observed (Palacios, Rodrõ Âguez- Jaramillo & Racotta 1999; Palacios, Ibarra & Racotta 2000). This study assessed the effect of spawning order on the quality of the spawns using biochemical and production techniques. Materials and methods Third-generation, pond-reared adult white shrimp, Penaeus vannamei (Boone), were brought to Aquaculture Research, 2003, 34, 427±435 ß 2003 Blackwell Publishing Ltd 427