Giant Clams Cycle in Palau

 BACKGROUND INFORMATION ON THE TAXA

The Indo-Pacific family Tridacnidae comprises two genera, Tridacnae
Brugui’ere with five species: Tridancnae gigas (Linne), T. gigas (Linne),
T. drasa (Roding); T. derasa (Lamarck,), T. maxima (Roding), and T. crocea (Lamarck); and the genus  Hippopus represented by the species
Hippopus hippopus and Hippopus porcellanus. Giant clams of the family Tridacnidae have been seriously considered as maricultural candidates. The first successful laboratory rearing occurred 3 decades ago
(LaBarbera, 1975; Jameson, 1976) and mass culture techniques were
not demonstrated until 1982 (Heslinga et al., 1984b).


Scientific and common names
The classification of giant clams is as follows:
Phylum: Mollusca
Class: Bivalvia
Order: Veneroida
Superfamily: Cardiacea
Family: Tridacnidae


Tridacnid clams are protandric functional hermaphrodites which
reproduce by broadcast spawning (Wada, 1954). Early growth rates
are rapid (50-100 mm per year for maricultured T. derasa and T. gigas)
compared to other bivalves, but the onset of sexual maturity is relatively late. Palauan  T. derasa reach male phase maturity at 3 years
post-fertilization and full maturity at 5 years (Heslinga et al., 1984b,
and unpublished data). Wada (1942) reported that T. squamosa and H.
hippopus in Palau reach full maturity at 160-200 mm and 130-150 mm,
respectively, which is about 3-5 years post-fertilization. Tridacna maxima
in Tonga reaches male phase maturity at about 55 mm (2.5 years), and
50% are fully mature at 105 mm (5 years) (McKoy, 1979). Jameson (1976)
found that T. maxima at Guam attains full maturity at 110-130 mm.

Palau Case Study