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Abstract
This study aimed to evaluate the effects of the density of Zooxanthellae (Symbiodinium microadriaticum), and salinity on giant clam larvae under artificial conditions. Two experiments were carried out, including two expriments .1) Effect of Zooxanthellae density on growth and survival rate of scaly giant clam larvae (Exp.1); and 2) Effects of salinity on growth and survival rate of scaly giant clam larvae (Exp.2). The larvae were reared at the density of 5 individual/mL in fiberglass tanks (100 L/tank). The water quality in the experimental tanks was as follows, temperature at 27.23±2.34 ºC, pH at 8.1–8.2, and dissolved oxygen at 5.3± 0.53 mg/ L. In Exp.1, the giant clam larvae of 3-day-old were fed with Zooxanthellae at 4 diffrent densities (with 6 replicates per treatment), including 1,000, 3,000, 5,000 and 7,000 cells/mL. The Zooxanthellae were daily fed to the larvae from 4-day-old, until those larvae were reached the pediveliger stage (8 days old). These results showed that the larvae from symbiotic algal density of 5,000 cells/mL obtained the highest growth in shell length, SGR, and survival rate (213.67±1.2µm, 6.20±0.21 and 56.50 ±0.45 %, respectively). In Exp.2, the giant clams of D-stage larvae (1-day-old) were reared at 4 different salinity treatments (with 6 replicates per treatment), including: 24, 27, 30, and 33 ppt. The results showed that at salinity 30 and 33 ppt the giant clam larvae obtained the highest in shell length, DGR, SGR and survival rate. Of which, at 30 ppt giant clam larvae shell length, DGR, SGR and survival rate were 224.50 ± 1.87µm, 12.07 ± 0.26 µm/day, 6.72 ± 0.12 and 33.17± 1.47 (respectively). Meanwhile, at salinity 24 ppt the giant clam larvae were performed the lowest growth in shell length (206.50 ± 3,27µm), DGR (9.50 ± 0.47 µm/day), SGR (5.60 ± 0.23) and survival rate (21.33 ± 1.63%).
Keywords: Giant clam, Tridacna squamosa, Zooxanthellae, salinity, growth rate, survival rate