A Little Bit More
Freshwater mussels or clams (the names are interchangeable) are common in unpolluted streams, rivers, and lakes, yet their life history is not well known. While all clams undergo a free-swimming larval stage that is very different from the adult, the freshwater clam is unique by being parasitic on fish.
Young freshwater clams hatch within the gill-folds of their parent and are bathed in a nutritious mucus for a time before release. Upon release, the immature larvae (glochidia) exit through the excurrent (outgoing) siphon of the parent. Once free, the glochidia settle to the bottom awaiting contact with a fish. Some clam species are host specific and infect only one species of fish; others may infect a variety of host species. Attachment to a fish is a matter of life and death and must be accomplished within several days if the mussel is to survive.
Glochidia are extremely sensitive to touch and clamp tightly on contact with a host. A glochidium’s opportunity comes if a fish brushes against the bottom, stirs up the bottom and larvae with fin movement, or takes temporarily suspended larvae into its oral cavity. Once a glochidium is attached, the fish exudes a slimy substance that encapsulates the larva. The glochidium projects as a small “pimple” on the fish and absorbs nutrients while developing the necessary vital organs for life on its own. After a few weeks the glochidium is completely developed. It then burst out of its capsule and falls to the bottom, by now some distance from its point of origin. From this point on the clam begins to develop a shell and slowly increases in size and looks like a typical clam.
Respiration and feeding.
Definitions
Disperse: to be widely spread or scattered
Activities
Clam Up
Objectives: See clam behavior
Materials: Clam, sand/fine gravel, aquarium
Although acquiring live clams for study will not be easy for some, this activity will provide your students with a window on a world they have rarely seen or even thought about. You may be able to purchase LIVE clams in a supermarket and these will almost certainly be from saltwater, not fresh. Despite this fact, you can place them in freshwater and they will live a short while and act “normally”. If you can provide either real saltwater or come up with a manmade substitute, your saltwater clams will last much longer.
Clams from both fresh and saltwater can be brought indoors for closer observation in an aquarium. Sand or fine gravel should be provided on the bottom so their trails will be easy to see as they slowly move across the substrate. Their trails often look like shallow trenches in the bottom. You may find that the clams are more active at certain times of the day than others and this would be interesting to note.
On close inspection you should be able to see the incurrent (incoming) and excurrent (outgoing) siphons as water is drawn into the animal and water is expelled. If the water isn’t perfectly clear, it will be easier to see the water entering and leaving the clam as you’ll be able to see tiny particles moving about. The food of clams consists of zooplankton (tiny animals living in the water column) and phytoplankton (tiny plants living in the water column) that is removed from the stream of water that enters the siphon. Providing the right kind of food for clams in an aquarium will be difficult so it’s suggested that you keep the animals for just long enough for students to observe their behavior and then return them to the site of their collection.
If you have an aquarium with green water (lots of tiny algae floating around) clams may actually help you clear the water as they feed. You can place a clam or two up next to the front glass so you can see their siphons more easily at work. Depending on the size of the aquarium and number/size of your clam, you may actually be able to see an increase in clarity after the clam has been filtering the water. Zebra Mussels, an alien clam in some North American lakes and rivers, have had a marked effect on water clarity due to their filtering out much of the plankton. Keep in mind that it’s not obvious when a clam has died and it can foul your aquarium very quickly if you don’t remove it. You’ll need to keep a close eye on your clams to be sure they’re still alive.
Key Concepts
Life Cycles, Predator/Prey Relationships, Structures and Functions
Questions
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Posted by adam greenan on February 25, 2006 at 07:41 AM
Q: Hi, I have a freshwater clam in my tropical tank, and it has spread it's young into the water. Most of my fish have several attached to them. Will this harm the fish and/or led to there death (I'm worried as alot of the fish are small. And if so, is there any way to remove the young without hurting the fish or the adult clam?
A: I've never known anyone who has had this happen - I think it's really neat! I can understand why you may be concerned about your fish but you'll do more damage trying to remove the glochidia (immature freshwater clams)from the fish than if you just leave them. I'd be sure that my fish were well fed - the glochidia will be absorbing nourishment from the fish - and I would hope that all will be well. Once the immature clams are large enough, they should fall off and begin growth in your tank. If you haven't already seen our unit on clam baby dispersal, take a look at this site - www.enaturalist.org Sorry, but I can't give you any more info than this.
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Good luck to you, your fish, and your clams. Thanks for writing.
Posted by angel beks on February 04, 2006 at 03:11 PM
Q: what are some of the advantages of possessing a two opening digestive tract?
A: Wow, that's the first time I've had a question like this one! You're going to really make me think!! Seems to me that there is one main answer to this. I would have to say that the most important advantage of having a two-opening digestive tract is that it is much more efficient. Organisms that must expel undigested material from their digestive tract from the same opening that they consume food through are going to be less efficient at feeding than those organisms that can both eat and evacuate at the same time. If we use humans as an example, we know that we can eat a meal at noon while our breakfast is still being digested by our body. Hope this answer helps. Thanks for an interesting question.
Posted by Rob Zimmerman on March 26, 2005 at 03:59 PM
Q: In an established 75 gallon saltwater tank, I have a maximus clam. It has done very well, but when I placed it in the tank I put it too close to the rocks and it can't turn all around. It is partially covered by red polyps that have over run this rock formation. I was told never to move a clam because I could damage it's foot. WHAT SHOULD I DO TO MOVE IT??? THANKS, Rob
A: I'm no expert on clams but I can't imagine how moving one would damage its foot. A clam's foot is very muscular, tough and certainly movable by the clam. I think you should be able to move your clam into a different position without any damage to the animal. Guess if I were concerned about its well-being, I'd simply move it very gently. Actually, I'm surprised that the clam isn't moving about in your aquarium on its own! Good luck.
Posted by Dana Lapsley on March 12, 2005 at 09:50 PM
Q: Will a saltwater clam eat fish food if not what do I feed it.
P.S. I don't have algi.
A: Clams, both freshwater and saltwater, are filter feeders and obtain their food by screening bits of food from the water. Your fish food will not be possible for them to eat unless it were in tiny bits floating in the water column. But, food floating in the water like that will simply foul your tank.
I know what I'd try if I needed to feed a clam. I'd take the clam out of the tank and place it in a smaller tank and then crush some food into a jar, mix it well with saltwater then pour into the clam's tank. This will allow the clam to feed on this food but again, it will definitely foul the water so you'll need to take the animal out after, oh, say 4-6 hours, and dispose of the water. This sounds like a lot of work but it will keep your main tank clean and the clam "may?" get some food out of this procedure. You don't have to do this daily - maybe once a week. If you can place some saltwater in a jar and set it on the windowsill so it can get plenty of light, you should quickly get some green water (lots of algae growing there). You could then feed that to your clam in a separate tank. If you do this, you can let the clam filter the water until all of the green color is gone. My best to you.
Posted by Clinton on August 22, 2004 at 08:44 PM
Q: I found a clam in the Laguna Madre at Corpus Christi, TX and am wondering what the blue "dots" are around the upper and lower 'lips' when the clam opens it mouth?
A: I'm not familair with your area but it sounds as though your clam is from saltwater. There are lots of different kinds of saltwater mollusks but I think I know what you've seen. The scallops have a row of brightly colored "eyes" along their mantle that you can see when the shell is almost, but not completely, closed. Although these function as light receptors, they aren't very discerning eyes and probably can only note sudden changes in light intensity as when a shadow falls on them. Compare the shape of your clam's shell to that of the Shell logo for the gas company and I think you'll have your clam. Thanks for asking.
Posted by Charles E on July 04, 2004 at 10:16 PM
Q: How do I keep a saltwater clam alive in my home as far as food goes. What do I feed it?
A: As you probably already know, clams are filter feeders and rely on floating bits of plant and animal material they can obtain from the water as their food source. Outside of constantly renewing the water in your tank, I'm not familiar with what you might be able to feed your clams. I could believe that if there is a lot of algae in the water (green water), this might serve as a food source, at least in part. Try asking your local pet store if they know of any packaged foods that could be added to the tank as food for your clams. Be careful that any foods introduced are used up before adding more or you'll foul up the tank. Good luck.
Posted by Erin, Paul, on March 23, 2004 at 02:55 PM
Q: Hi! We have three questions for you.
1. Do saltwater clams disperse their eggs differently than fresh water clams?
2. How do clams catch their prey/food?
3. Why do clams put their larvae on fish?
Thanks, from a small class (4 kids) in a little school, in a tiny town in Southeast Alaska!
A: > 1. Do saltwater clams disperse their eggs differently than fresh water clams? Actually, it's the larvae that are dispersed, not the eggs. The eggs remain in the adult until they've hatched. The marine (saltwater) clams have free-swimming larvae that can swim in the water column using tiny hairs (cilia). Once they are old enough, they settle to the bottom and become what we think of as typical clams.
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> 2. How do clams catch their prey/food? Look again at the illustration just below the "A Little Bit More" and you'll notice the clam I've drawn has two siphons - one an intake and one an outgoing siphon. Water flows into the incoming siphon and the clam removes tiny bits of plant and animal life to digest and then the outgoing siphon ejects what's left.
> 3. Why do clams put their larvae on fish? Why questions are difficult ,if not impossible, to answer in science. All we know is that this procedure has evolved over a great deal of time and works for these animals. Different animals come up with different "strategies" or ways of doing things - those that work are kept, those that don't work fade away.