WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2019 55 obtained from natural spawns were fertilized by exposure to dilute sperm suspension for 30-90 min at 28 C and 33 ppt salinity. They were then rinsed onto a 20-µm polyethylene-screen and transferred to 4-L beakers filled with 1-µm filtered seawater at a density of 80 eggs/mL. Larvae were not fed until 24 h after fertilization, then they were fed daily with microalgae cultures from 1 × 104 cells/mL to 3 × 104 cells/mL. Eggs were discharged from the exhalent siphon (Fig. 7) and were round, ranging from 70-80 µm in diameter. Larval development can be seen in Figure 8. A ciliated swimming gastrula developed six hours after fertilization. By 12 hours after fertilization, most embryos were trochophore larvae, 77 µm in maximum height. Early veligers (80-90 µm) form 24 h after fertilization. Phytoplankton were first observed in the gut of the planktonic veligers on the fourth day. Pediveliger larvae were observed on day 10 (170-180 µm). This stage is very brief, lasting approximately 24 h. Two different daily feeding schemes were tested, one with Tisochrysis lutea only and the other with a mixture of 50 percent T. lutea and 50 percent Tetraselmis suecica. The two different feeding schemes did not affect larval survival. • Comparison of growth in the natural environment and in the laboratory: Growth and survival of adult specimens were determined at a beach tidal zone and at the Aquaculture Laboratory, not exposed to tidal changes and with a supplementary daily addition of microalgae cultures (T. lutea, Chaetoceros muelleri and T. suecica) as food. Growth and survival of adult clams at the seashore and in tanks at the laboratory was not different after four months. Overall, the results indicate that spawning and larval development in captivity are feasible. Future research will be based on optimization of larval growth and survival and determination of the time required to grow settled larvae to 2 mm. Another step will be to continue grow-out trials at least for one year, analyzing and comparing growth, survival and body proximate chemical composition of clams maintained at the seashore and in the laboratory. Notes Sergio Nestor Bolasina, College of the Marshall Islands – Land Grant Cooperative Research & Extension, PO Box 1258, Majuro 96960, Republic of the Marshall Islands. E-mail: sbolasina@cmi.edu This work is a result of research sponsored by the National Institute of Food and Agriculture of the United States Department of Agriculture, under Land-Grant Hatch Project MIRCMI21: Species and System Selection for Sustainable Aquaculture in the Republic of the Marshall Islands. I. Culture potential of Pacific clam or jukkwe, Asaphis violascens (Forsskål, 1775). References Bueno, P. 2014. Lessons from past and current aquaculture initiatives in selected Pacific island countries. FAO, Rome, Italy. www.fao.org/3/a-i4139e.pdf Brander, K., L. Botsford, L. Ciannelli, M. Fogarty, M. Heath, B. Planque, L. Shannon and K. Wieland. 2010. Human impacts on marine ecosystems. Pages 41-71 In: M. Barange, editor. Marine Ecosystems and Global Change. Oxford University, Oxford, UK Catterall, C.P. and I.R. Poiner. 1987. The potential impact of human gathering on shellfish populations, with reference to some NE Australian intertidal flats. Oikos 50:114-122. Gillett, R.D. 2016. Fisheries in the Economies of Pacific Island Countries and Territories. www.sprep.org/attachments/VirLib/ Regional/benefish-gillett-16.pdf Harris, M. and M. Weisler. 2018. Two millennia of mollusk foraging on Ebon Atoll, Marshall Islands: Sustained marine resource use on a Pacific atoll. Archaeology in Oceania 53(1):41-57. Paulay, G. 2000. Benthic ecology and biota of Tarawa atoll lagoon: Influence of equatorial upwelling, circulation, and human harvest. Atoll Research Bulletin No. 487. Poutiers, J.M. 1998. Gastropods. Pages 363-648 In: Carpenter, K.E. and V.H. Niem. 1998. FAO species identification guide for fishery purposes. The Living Marine Resources of the Western Central Pacific. Volume 1. Seaweeds, Corals, Bivalves, and Gastropods. FAO, Rome, Italy. Rimmer M., L. Bell, M. Lober and A. Trevor. 2001. Evaluation of the potential for aquaculture in Samoa. Ministry of Agriculture, Forests, Fisheries and Meteorology, Government of Samoa. pimrisregional.library.usp.ac.fj/gsdl/collect/moanare1/index/ assoc/HASH0aff.dir/doc.pdf FIGURE 7. Spawning of Pacific clam. FIGURE 8. Larval development of the Pacific clam: (a) fertilized oocyte (75 µm), (b) trochophore, (c) early veliger, (d) D larvae and (e) pediveliger.
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