Reef Ramblings: Clamming Around
Part II: Spawning Tridacnids
Adam Blundell M.S.
Introduction
In the previous article I covered the many reasons why hobbyists would be interested in keeping Tridacnid clams.To sum up that article, Tridacnids are a perfect animal for captive care. For the more advanced hobbyists, or at least the more adventurous hobbyists, Tridacnid clams are potentially wonderful animals to aquaculture, experiment, and study.
What Has Been Done
Clams have come a long way. I’m most surprised by this because I don’t personally see many constituents pushing for advancements with clams, yet much progress has been made. Today thousands of clams are aquacultured. Many of these farmed clams end in the food system, but many find their way in to the marine ornamental industry. This is fabulous! Clams today are farmed in huge outdoor ponds and reaceways. It would be safe to say that the high price hobbyists pay for clams (compared to the food industry) has pushed the market towards the ornamental industry.
What Is On The Horizon
Clam farming may soon become a home-based project. It is quite probable and possible that clams will become commonly cultured animals. Imagine trading baby clams like trading coral frags. Imagine attending a fish geek conference and seeing a hobbyist with a tradeshow booth… with hundreds of baby clams for sale.
A clam in a holding tank
Reasons to Culture Clams
1) It can be done.
We are currently seeing great success with thousands of clams being commercially raised.
2) It is easy.
A very simple procedure and protocol has already been developed for simple clam culture.
3) Market availability.
You can sell clams all day long. Despite huge commercial aquaculture facilities already in place, many clams are still collected from reefs. Any local pet store can provide evidence that clams are selling as fast as ever before.
4) Cost effective.
One could argue the cost of time involved, but in terms of cash flow clams are cheap. They need just a few things to grow from larvae to adults: light, saltwater, fish poop.
5) High fecundity.
One spawning can occur in about 15 minutes. For some clams this can produce up to 500 million eggs. Just for a reference that means a hobbyist could have more clam eggs in one day than there are people in the entire United States. If only 1% of those larvae made it to market size that would still be twice as many clams as people in my home state. And that is from just one clam, on one day.
6) Space feasibility.
To culture a few dozen clams you would need a 10 gallon tank and a window sill. Even the most novice of hobbyists can convince their wife’s to give them that much room.
Spawning Clams
Thankfully I didn’t have to figure this out. Trial and error overseas has developed a great system for spawning clams. Some variations exist and have been covered well by Ellis and colleagues (Ellis 1998). Shown here is the procedure I follow.
A large whiteboard displays the procedure used in the lab
Adam’s Preferred Method (for more details please contact the author)Husbandry Stage
1- Obtain and house large reproductive sized clams. This size varies among the species, but for starters we’re looking at 5†Crocea clams.
2- Provide healthy conditions (lighting and carbonate sources).
Spawning Stage
1- Mix 16mg of Serotonin (5’-hydroxytryptamine) into 20ml of filtered seawater from the clam holding tank.
2- Have all beakers, containers, pipettes, and syringes labeled and in order.
Weighing out chemicals to stimulate clam spawning
Injection Stage
1- Select injection site. This varies from scientist to scientist but I currently subscribe to the theory of injecting BELOW the excurrent siphon. This is done nearly straight up and down by piercing through the mantle tissue into the internal organs.
2- Once you feel the needle make its way into the muscle mass or organ tissue, inject 2ml of the serotonin mixture (many authors recommend only 1ml).
3- Carefully remove needle and allow clam time to open back up.
Injecting Serotonin
The process of stimulating clams to spawn in captivity
Collecting Gametes
1- About 10 minutes after injecting clams the clam will begin to expel sperm. This can be easily pulled out with a pipette or by scooping it out with a cup. The sperm mixture is a cloudy white mixture.
2- About 10 minutes after the release of sperm you may get eggs. Not all clams are old enough and healthy enough to produce and release eggs. This is where proper selection of broodstock is important.
3- Collect the eggs mass, which looks very similar to the sperm released, except you can sometimes see granules (eggs) if you look closely. It should be noted that while I haven’t seen it reported before we noticed a difference in buoyancy between the sperm and eggs. In our tests the sperm floated upward into the water column while the egg mass decended down towards the base of the clam.
Clam releasing sperm into the water column
Fertilization
1- Mix the collected eggs solution into filtered seawater. I like to mix up enough water with the eggs to create a solution that is 1L in volume. And now prepare the sperm mixture. I have no way to really quantify the sperm count but I’ll do my best. Take all of the collected sperm from one clam and mix it with filtered seawater (from the clam holding tank). Mix enough water to make 500ml. From this solution I recommend using 5ml total for the fertilization process. This number will surely change with further studies but appears to be a good starting place this early in the research. The sperm are mixed with the eggs. WARNING- too little sperm is never a problem, too much sperm causes numerous problems. When in doubt, use less sperm.
2- The eggs are reported to be viable for 15 minutes post release from various sources. For this reason using sperm and eggs from several clams can be challenging as you are racing against time.
3- Fertilization in marine invertebrates is often instantaneous. Far more control factors and recognition sites are present on sperm-egg combinations than are found in animals like humans, dogs, horses, fishes. However, it should be noted that Tridacnids appear to be a bit of an anomaly as their fertilization process does not quickly prevent polyspermy. In fact it is quite easy to “over fertilize†an egg in laboratory settings. I hypothesize that this may also happen in natural conditions and may contribute to their very low success rate.
Tridacnid sperm and eggs as seen through a microscope
Grow Out Stages
1- This will be reported in the next installment of this series.
Conclusion
While the process of rearing clams is still in its infancy, the process of spawning clams is now a reality. It is my hope that this article will help encourage a handful of hobbyists to take the plunge.
Finally I’d like to thank two of my great friends. Clam gurus James Fatherree and Shane Silcox have provided the key ingredient for my clam studies… enthusiasm. My thanks to the two of you.
Glam Guru- Shane Silcox
James Fatherree and Adam Blundell
Author Information
Adam Blundell M.S. is a hobbyist, lecturer, author, teacher, and research biologist. Adam works for the University of Utah in Pathology and in Marine Biology. He currently helps run the Wasatch Marine Aquarium Society, of which he is a former president. Adam is also the director of the Aquatic & Terrestrial Research Team, a group which bridges the gap between hobbyists and scientists. Adam can be reached by email on his author forum.
References and Suggested Readings
Ellis, S. (1998) “Spawning and Early Larval Rearing of Giant Clams (Bivalvia: Tridacnidae)â€, Center for Tropical and Subtropical Aquaculture.
Fatherree, J. (2007) “Giant Clams in the Sea and the Aquariumâ€, Liquid Medium. Tampa FL, USA.
