WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2017 33 the breeding peak. This strategy was followed because winged pearl oysters breed throughout the winter-spring and display several spawning peaks as long as water temperature remains low (Saucedo and Monteforte 1997). Consequently, results of gonad condition (quality) and larval vigor (performance) may substantially differ in all trials from prevailing biotic and abiotic traits. For example, rearing temperatures greatly varied from 17-24 C (Araya-Nuñez et al. 1991, 1995, McAnally and Valenzuela 1990, this study) to 27.5-28.5 C (Serrano and Salinas 1993). Although faster growth of larvae is expected at higher temperatures, spread of harmful bacteria is also greater and may become a problem. The time needed to reach the settlement stage was also different in all trials and occurred as early as day 19 in our study, or until day 26 (Serrano and Salinas 1993), day 33 (McAnally and Valenzuela 1990), or day 39 (Araya-Nuñez et al. 1995). In Araya-Nuñez et al. (1991) metamorphosis never occurred because larvae remained between veliger and umbo stages and suffered high mortality. The delay or failure of larvae to complete metamorphosis and settle may suggest poor gonad condition of breeders or unsuitable rearing conditions, but may also reflect differences in material, color, surface, and other physical and chemical cues of the artificial collectors used (Saucedo et al. 2005). Substrates varied from simple plastic fiber bags (this study), plastic frames with nylon cords (McAnally and Valenzuela 1990), mussel shell chips and polypropylene threads (Araya-Nuñez et al. 1995), or a combination of natural and artificial materials such as scouring pads, oyster shells, shade cloth and plastic discs (Serrano and Salinas 1993). Despite these differences, the final yield of spat was very similar in all trials (17-21 percent). Based on these outcomes, a deep analysis of the relationship between broodstock condition and larval viability is recommended to maximize production of winged pearl oyster spat used for pearling activity, considering two key moments: 1) when early veliger larvae start exogenous feeding after exhausting yolk reserves, and 2) when late pediveliger larvae use their energy reserves to complete metamorphosis and settle. Analyzing the interactive effects of traits such as temperature, diet, and stocking density is also necessary. Acknowledgments Mario Osuna-García, Delfino Barajas-Frias, and Pablo Ormart-Castro (all at CIBNOR) are acknowledged for assistance in culturing the larvae; Hector Acosta-Salmón for valuable comments; and Ira Fogel for editorial services. Douglas McLaurin (from Perlas del Mar de Cortez) kindly provided a photograph of Pteria sterna round pearls. Funding came from internal CIBNOR grants (PAC-3.3). Notes Pedro E. Saucedo, Aquaculture Program, Centro de Investigaciones Biológicas del Noroeste (CIBNOR), Calle I.P.N. 195, La Paz, B.C.S. 23096, Mexico, Tel: +52 (612) 123 8484; Fax +52 (612) 125 3625; psaucedo04@cibnor.mx 1 Media Cybernetics, Bethesda, MD References Araya-Nuñez, O., B. Ganning, and F. Buckle-Ramírez. 1991. Gonad maturity, induction to spawning, larval breeding, and growth in the American pearl-oyster (Pteria sterna, Gould). California Fish and Game 77:181-193. Araya-Nuñez, O., B. Ganning, and F. Buckle-Ramírez. 1995. Embryonic development, larval culture, and settling of American pearl-oyster (Pteria sterna, Gould). California Fish and Game 81:10-21. Gervis, M. and N. Sims. 1992. Biology and Culture of Pearl Oysters (Bivalvia: Pteriidae). Overseas Development Administration of the United Kingdom. International Center for Living Aquatic Resources Management, Manila, The Philippines. Haws, M.C, S.C. Ellis and E.P. Ellis. 2006. Producing half pearls (Mabe). Western Indian Ocean Marine Science Association, University of Dar es Salaam, University of Hawaii, Hilo, Coastal Resources Center, University of Rhode Island. Kiefert, L., D. McLaurin, E. Arizmendi, H.A. Hänni and S. Elen. 2004. Cultured pearls from the Gulf of California, Mexico. Gems & Gemology 40:26-38. Martínez-Fernández, E., H. Acosta-Salmón, C. Rangel-Dávalos, A. Olivera-Bonilla, H. Ruiz-Rubio and A. Romo-Piñeira. 2003. Spawning and larval culture of the pearl oyster Pinctada mazatlanica in the laboratory. World Aquaculture 34(1):36-39. McAnally, L. and E. Valenzuela. 1990. Growth and survival of larvae of the pearl oyster Pteria sterna under laboratory conditions. Ciencias Marinas 16:29-41. Monteforte, M., E. Kappelman and B. López. 1995. Spatfall annual survey of pearl oyster Pteria sterna (Gould) in experimental collectors at Bahía de La Paz, South Baja California, Mexico. Aquaculture Research 26:497-511. Saucedo, P.E. and M. Monteforte. 1997. Breeding cycle of pearl oysters Pinctada mazatlanica and Pteria sterna (Bivalvia: Pteriidae) at Bahía de La Paz, Baja California Sur. México. Journal of Shellfish Research 16:103-110. Saucedo, P.E., H. Bervera-León, M. Monteforte, P.C. Southgate and P. Monsalvo-Spencer. 2005. Factors influencing recruitment of hatchery-reared pearl oyster (Pinctada mazatlanica; Hanley, 1856) spat. Journal of Shellfish Research 24:215-220. Saucedo, P.E., P. Ormart-Castro and M. Osuna-García. 2007. Towards development of large-scale hatchery cultivation of larvae and spat of the pearl oyster Pinctada mazatlanica (Hanley, 1856) larvae and spat in Mexico. Aquaculture 273:478-486. Serrano, S.J. and D. Salinas. 1993. Cultivo de larvas y producción de semilla de Pteria sterna (Mollusca: Bivalvia) en un criadero comercial. Revista de Investigaciones Científicas 4:81-90. Southgate, P.C. 2008. Pearl production. Pages 231-272 In: P.C. Southgate and J.S. Lucas, editors. The Pearl Oyster. Elsevier Science, Amsterdam, Netherlands. FIGURE 4. Cultured round and semi-round pearls formed by winged pearl oysters at Perlas del Mar de Cortez, Guaymas, Gulf of California, Mexico. Photo: Douglas McLaurin-Moreno.
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