A study was conducted on the growth and survival rates of diploid and triploid tropical oyster (Crassostrea iredalei) larvae cultured in the hatchery at NAPFRE and grown out thereafter, at the Teluk Bayu River in Batu Lintang, Kedah. Triploidy was induced on strip-spawned eggs using Cytochalasin B (CB) at optimal concentration of 0.75 mg/l. Chromosome analysis showed that 81% triploid embryo (chromosome count) were produced during the induction. A comparison of the mean length and width (± SE) was found to be significantly different at p< 0.05 for the triploid and diploid oyster larvae. The triploid larvae attained a mean length of 336 ± 3.41 gm as compared to the diploid which measured 263 + 3.41 gm, while the mean width was 293 ± 3.03 gm and 229 ± 3.03 gm for the triploid and the diploid larvae, respectively. A fifteen month study was conducted to compare the growth and survival rates of the diploid and triploid oyster spat cultured at the Teluk Bayu River in. Batu Lintang, Kedah. Although the triploid oysters attained a larger mean length of 79.3 ± 0.97 mm as compared to the diploid oysters which measured 70.8 1.02 mm, they were not significantly different (p>0.05). A comparison of the mean total weight at the end of the experiment was found to be significantly different (p <0.05) for the triploid and diploid oysters, which was 94.0 1 1.29 g and 69.1 + 1.4 g, respectively. It was observed that the triploid oysters were on the average, 36% heavier than their diploid siblings after 15 months of culture. However, when marketable sized oysters were analysed for their ploidy level (gill tissue cell nuclei diameter) only 53% were found to be triploids.