Tridacna gigas Breeding Guide: Hatchery Mariculture of the Giant Clam

Tridacna gigas, the world's largest bivalve, reproduces by broadcast spawning and releases over 500 million eggs at once. It is CITES II listed and reared only in mariculture hatcheries, never in home aquariums.

Overview

Tridacna gigas is the largest living bivalve mollusc; the largest known specimen measured 137 cm and weighed about 250 kg alive, with a dead specimen recorded at 333 kg. It derives roughly 65-70 percent of its nutrition from symbiotic zooxanthellae housed in its mantle, which lets it reach over a metre even in nutrient-poor reef water. It is not a home-aquarium animal and is reared only at mariculture scale.

Reproductive Mode

T. gigas reproduces sexually and is hermaphroditic, producing both eggs and sperm, though self-fertilization does not occur. It uses broadcast spawning, releasing gametes into the water. A chemical called spawning-induced substance (SIS) synchronizes release among neighbouring clams. A single adult can release more than 500 million eggs at a time, with eggs around 100 micrometres in diameter.

Propagation Setup

Mass culture of T. gigas began in Palau in the 1980s. Australia funded major hatchery projects between 1985 and 1992 at James Cook University, supporting hatchery development across the Pacific and the Philippines. Broodstock spawning is induced in controlled facilities and gametes are collected for rearing.

Spawning and Larval Rearing

A fertilized egg floats for roughly 12 hours before a trochophore larva hatches. Within two days larvae measure about 160 micrometres and develop a foot. Larvae are initially aposymbiotic and capture free-floating zooxanthellae while filter feeding, then settle around one week of age. Juveniles reach about 20 cm; laboratory-reared clams grow roughly 12 cm per year.

Common Challenges

Beyond the impossibility of rearing planktonic larvae in a display tank, T. gigas reaches a size suitable only for public aquaria or open-water mariculture. Slow growth, immense final size and strict trade controls mean propagation is restricted to specialist institutions, not hobbyists.