Regular followers of our Facebook Page will know we have been busy kicking off the Gaint Clam Farm project and populating it with lots of cuddly clam babies. In this post we’ll get you fully up to date with what’s been going on, where we are, and what’s coming next.
A Brief Introduction to Giant Clams
Before bringing giant clams into the world, it’s essential to know what flavours they come in. The boy/girl choice is the easy bit – quite handily they are both. A few more options are available when we look at the individual species. There are 10 within the genus Tridacna, plus two other species commonly recognised as giant clams.
Our giant clam farm is populated by four of the species from the Tridacna genus:
Small Giant Clam (Tridacna Maxima)
The Maxima Clam, also known as the Small Giant Clam, is a species found throughout the Indo-Pacific region. They are much sought after in the aquarium trade, as their often striking coloration mimics that of the true giant clam; however, the maximas maintain a manageable size, with the shells of large specimens typically not exceeding 20 centimetres (7.9 in) in length. The small giant clam has the widest range of all giant clam species. It is found in the oceans surrounding east Africa, India, China, Australia, Southeast Asia, the Red Sea and the islands of the Pacific. Found living on the surface of reefs or sand, or partly embedded in coral, the small giant clam occupies well-lit areas, due to its symbiotic relationship with photosynthetic algae, which require sunlight for energy production.
Fluted Giant Clam, or Scaly Clam (Tridacna Squamosa)
So called for the large, leaf-like fluted edges on its shell. The mantle shell colors vary from browns and purples to greens and yellows arranged in elongated linear or spot-like patterns and grows to 40 centimetres (16 in) across. the clam’s mantle tissues act as a habitat for the symbiotic single-celled dinoflagellate algae (zooxanthellae) from which it gets a major portion of its nutrition. By day, the clam spreads out its mantle tissue so that the algae receive the sunlight they need to photosynthesize
Southern Giant Clam (Tridacna Derasa)
The southern giant clam is one of the largest of the “giant clams”, reaching up to 60 cm in length. The mantle usually has a pattern of wavy stripes or spots, and may be various mixtures of orange, yellow, black and white, often with brilliant blue or green lines. It is native to waters around Australia, Cocos Islands, Fiji, Indonesia, New Caledonia, Palau, Papua New Guinea, Philippines, Solomon Islands, Tonga and Vietnam. Populations have also been introduced to American Samoa, Cook Islands, Marshall Islands and Samoa, and reintroduced after extinction in Guam, the Federated States of Micronesia and Northern Mariana Islands. The southern giant clam is found on the outer edges of reefs at depths of 4 to 10 meters.
Teardrop Giant Clam (Tridacna Noae)
A newly recognised species distinct from Tridacna Maxima, identifiable by the mantle pattern and coloration, and also gene sequencing which is slightly more difficult for the casual observer! Teardrop Clams are unmistakable are distinguished by the presence of the teardrop pattern on the mantle and a neat row of eyes on the edges of the mantle, whereas these are much more spread out in Tridacna noae. Teardrop clams have a fairly wide distribution which overlaps with maxima clams; gold teardrop clams are commonly available from Vietnam and blue teardrop clams sporadically appear in the trade from Australia and the Indo-Pacific.
Preparing the Nursery
Any well organised parent-to-be will consider the nursery requirements for their future offspring and prepare accordingly. So, before getting down to the fun part of making babies we began construction of the giant clam hatchery on Matagi Island with some major assistance and guidance from the godparents, the Douglas family.
The photos below show the growing raceways at our Lali station – also suitable for raising sea cucumbers – and spawning tanks residing at the Christene Station hatchery awaiting installation of pumps and pipes.
Clams have a lot of babies – and we mean a lot.
Back in June 2017 we successfully spawned 120 million Tridacna Maxima into the newly constructed hatcheries. With expert technical advice on creating the perfect environment for these little critters the hopes were high that the maximum number possible would survive and become viable giant clams. Since 10% of the offspring are earmarked for reef rehabilitation projects we had even more reason for a high survival rate.
In August we followed with a spawning of Tridacna Squamosa – the Fluted Giant Clam, and a week later the Southern Giant Clams Tridacna Derasa.
To confirm fertilisation we cheekily, but politely, requested use of the excellent microscopes at Taveuni Hospital. The staff generously said Yes (Fijians rarely say No) and we took our tiny samples off island and on 60 km sea and road trip.
Using a Samsung mobile phone camera 1 cm from the objective lens of their nifty Olympus microscope we got the first DIY equivalent of a sonar scan showing our babies were alive and well. Microscopes are on the 2018 Christmas wishlist for Santa !
A follow up visit 3 weeks later and we could clearly see the already well established symbiotic algae zooxanthellae inside the Tridacna Derosa – this will partner with the clam for the rest of its life. Super exciting stuff for us! In addition, healthy 5 week old Tridacna Squamosa, and 7 weeks old Tridacna Maxima and Tridacna Noae.
Raising offspring requires a commitment of time, effort, and money, and the returns and rewards on that investment come much later down the road. Right now we are jumping up and down as the fruits of our labours are actually visible with the naked eye – no need now for hospital visits or microscopes. Clearly visible in our nursery tanks lay baby clams approximately 4-6 millimeters long nestling nicely within the algae, and multiplying rapidly.
By November the Tridacna Squamosa from our 2nd pool were settled on inverted tiles in such numbers they would need thinning out, and in January they too were looking good and growing well. At 6 months old they are already half the size of our export shipping size.
This whole project is starting to look very real, and to date a great success. And 10% of these guys will go back in the ocean for local reef rehabilitation projects – a fantastic bonus for us, the community, and the environment.
Our children eventually grow up and leave home. Our giant clams are primarily earmarked for export and for that to happen we must satisfy all the relevant authorities that our process and product is up to scratch. Inspections and certifications are required, and the Minsistry of Fisheries team as well as Permanent Secretary Mr Sanaila Naqali have visited to ensure compliance. Also present for the visit, the chairman of the Vanua Trust of Laucala who is the legal representative of the traditional Fishing Right Owners. Once all the checks are done and boxes ticked we will be ready to send Civa’s Giant Clams out into the big bad world !
With special thanks to…
Many thanks to Douglas family from Matangi Private Island Resort, Fiji who have been steadfast and constant in their support, and to Dr Paul Southgate and Dr Pranesh Kishore from the University of the Sunshine Coast and Tropical Aquaculture Research for their continuous technical support. Also Beero Tioti from Pacific-Community-SPC for the constant tips of do’s and dont’s.
Photo credits – Civa Fiji Pearls, Paul Jelley