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Oysters are key species in the functioning of coastal ecosystems, accomplishing or performing various ecological roles, in addition to being an important source of food (Bayne, 2017). Of the three commercially important genera of oysters, Saccostrea, Ostrea and Crassostrea, the latter has the greatest development potential due to its high tolerance to estuarine conditions and usually abundant spatfall (Angell, 1986). In the Philippines, there are four species of oysters-Crassostrea iredalei, C. malabonenis, C. palmipes and Saccostrea cucullata (Lovatelli, 1988;Samsin, 1988). The most popular and commercially desirable among these is the slipper oyster or Crassostrea iredalei (Faustino, 1932), which grows at a faster rate to a larger size and has a straight shell margin making it easier to open (Samsin, 1988). This species is larger than the other Crassostrea species in the country and can grow up to 15 cm shell length in a favourable environment (Poutiers, 1998), hence very ideal for culture. According to anecdotal reports of oyster growers, C. iredalei can grow to 12-15 cm shell length when left undisturbed on the settlement substrate for around two years. Although considered endemic to the Philippines (Poutiers, 1998) and has not been reported in other countries until the mid-1990s (Garrido-Handog, 1990Rosell, 1991), C. iredalei is now grown in Malaysia (Devakie & Ali,