Reproduction and Early Juvenile Growth of the Giant Clams Tridacna noae and Tridacna maxima in Taiwan

The reproductive cycle, larval development, and juvenile growth of Tridacna noae and Tridacna maxima were investigated to improve their hatchery production for conservation and commercial use in Taiwan. To study the giant clam reproductive cycle, hypodermic extraction of oocytes from T. noae and T. maxima was conducted in Dongsha and Kenting, Taiwan, from March 2013 to May 2014; ripe eggs were observed in both species from March to August. There was no apparent correlation between reproduction and water temperature. Artificial fertilization was successfully conducted in T. maxima, T. noae, and a hybrid of T. maxima female/T. noae male. The diameter of fertilized eggs was 99.0 +/- 8.1, 113.8 +/- 18.5, and 116.3 +/- 6.2 mu m, respectively. On day 6, the hybrid died. Tridacna maxima grew more than T. noae in both 1-and 10-month-old juveniles. The juvenile growth of T. noae was compared between the artificial breeding sites of Penghu and Linbian, which represent the main ornamental aquatic animal culture areas of Taiwan. Starting with individuals with a shell length of 15.9 +/- 2.5 mm (265 days old), the juveniles observed in Linbian were significantly larger than those in Penghu, i.e., 26.6 +/- 3.6 mm on day 307 vs. 18.6 +/- 2.9 mm on day 321 (p < 0.001). This might be linked to the differences in local water temperatures between the two locations, i.e., 20.3-27.0 degrees C vs. 16.9-23.9 degrees C, respectively. These results can be used to further research ways to maximize spat production and minimize giant clam operational costs.