Growth performance of slipper-cupped oyster (Crassostrea iredalei Faustino, 1932) larvae and spat fed with different microalgae

Interest on oyster culture is increasing worldwide. In Malaysia, slipper-cupped oyster, Crassostrea iredalei is preferred as potential commercial species due to its sweet flavor and creamy colored meat. However, at the moment, oyster culture is still dependent on natural seed collection. Seed can only be collected for a short period during certain seasons with unpredictable recruitment. Therefore, the production of seedling from hatchery is essential for the sustainable production of oyster. Further research should be carried out to determine the growth and survival of oyster larvae produced in hatchery. This study specifically addressed the feeding aspect of oyster in hatchery. Three species of microalgae used in this study were Isochrysis sp. Pavlova sp. and Chaetoceros sp.. They were fed to larvae (D-stage and umbo stage) and spat of C. iredalei. Effects of feeding three microalgae species on the growth of D-stage and umbo stage larvae C. iredalei were investigated. One-day-old larvae (after fertilization) were reared for six days, while seven-day-old larvae (after fertilization) were reared for fourteen days. Diet using Isochrysis sp. supported the highest (p<0.05) growth while Chaetoceros sp. showed the lowest growth for D-stage larvae. Larvae fed with diet Isochrysis sp. showed the highest final, increment of shell length and growth (85.45 ± 7.72 μm, 22.07 ± 7.72 μm, 0.05 ± 0.02 μm/day, respectively). Meanwhile, diet combination of flagellate and diatom supported better growth for umbo stage larvae. Combination diet Pavlova sp. and Chaetoceros sp. gave the highest (p<0.05) growth, compared to combination of Isochrysis sp. and Pavlova sp. (lowest growth). Combination of Pavlova sp. and Chaetoceros sp. showed the highest final, increment of shell length and growth (265.89 ± 22.50 μm, 184.13 ± 22.50 μm, 0.08 ± 0.01 μm/day, respectively). Survival of D-stage and umbo stage larvae in every diet showed no significant differences. These results suggested D-stage larvae need Isochrysis sp. for better growth. While at umbo stage, diets containing combination of flagellate and diatom are better for the growth of this species. The effect of feeding three microalgae species on the early development of C. iredalei spat was conducted. Early spats were reared for three weeks in container. Spat in all treatments survived well since there were no mortality. There was no significant difference (p>0.05) between diet Isochrysis sp./Chaetoceros sp. (IC) and Pavlova sp./Chaetoceros sp. (PC). Both binary diets show high significant difference (p<0.05) toward diet Chaetoceros sp. (C). Diet IC showed highest final, increment of shell length and growth (6.240 ± 0.186 mm, 2.740 ± 0.193 mm, 0.0276 ± 0.002 mm/day, respectively). Diet C supported the lowest of final, increment shell length and growth (5.413 ± 0.486 mm, 1.947 ± 0.365 mm, 0.0211 ± 0.003 mm/day, respectively). As for fatty acid level, Isochrysis sp. showed high content of docosahexanoic acid (DHA), Pavlova sp. rich in saturated fatty acid (SFA) while Chaetoceros sp. rich in polyunsaturated fatty acid (PUFA), eicosapentanoic acid (EPA) and arachidonic acid (AA). The lack of DHA in diet C resulted in low growth of spat. Thus, this result suggested the combination of diatom and flagellate produced better growth for early stage of C. iredalei spat. As a conclusion, at the early stage of larvae development, Isochrysis sp. is essential as compared to diatom since it can be easily digested. However, as larvae growth, they need combination of flagellate and diatom.

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