Larval and early juvenile culture of two giant clam (Tridacninae) hybrids

The capacity for inter-specific hybridisation to yield improvements in animal production has long been realised in the aquaculture sector. However, the extension of hybridisation to improve production of giant clams (Tridacninae) has received little research attention. Aquaculture production of giant clams is directed primarily at aquarium markets, and hybridisation offers an opportunity to diversify available products. Here we report on the successful inter-specific hybridisation of Tridacna maxima and T. noae, and assess hybrid performance during hatchery culture. Both maternal and paternal hybrid crosses of T. maxima/T. noae yielded competent larvae. Fertilisation success was significantly lower (40.7 +/- 3.2%) for the T. maxima female/T. noae male cross compared to the T. noae female/T. maxima male cross (89.3 +/- 1.8%; chi(2) = 154.03, P < 0.01). Despite the disproportionate fertilisation success, the two hybrids had similar survival curves (survival = 2.03 x days(-2.08), r(2 )= 0.67, P = 0.13) for the first 30 days of culture. Antero-posterior shell growth (APM) was superior in the T. maxima female/T. noae male hybrid (APM = 10((2.158+0.019xdays))) when compared to the T. noae female/T. maxima male hybrid (APM = 10((2.169+0.016xdays))) over the same time frame (r(2) = 0.92, P < 0.001). Both survival and growth of the hybrids exceeded that reported in the literature for pure-strain hatchery culture of giant clam species. This suggests capacity for hybridisation to contribute to giant clam aquaculture production. The application of hybridisation to supply aquarium markets and necessary considerations for manipulating stock genetics are discussed in view of these results.