In a series of prey- choice experiments, 3 gastropod and 4 crustacean predators were each offered 3 Tridacna spp. and Hippopus hippopus. In a second series, T. gigas and H. hippopus were each offered to the gastropod Cymatium muricinum. Notes are offered on the methods of attack of the various predators. Overall, H. hippopus was the least vulnerable species of those tested. The use of trestles to raise nursery cages above the sea floor, and thus away from the range of benthic predators, was found to be effective in increasing survival. Further protective measures include the size and shape of cage meshes, and devices to prevent predators climbing the legs of trestles.