Rearing Horseshoe Crabs

     Rearing horseshoe crabs is not easy. We have tried to follow  the directions published by the Delaware Division of Fish & Wildlife. But, as the people who wrote the directions said, when they gave us permission to share these directions, there are always many different things happening which are hard to explain. There's so much they don't know, and problems arise that they don't have answers for. Often crabs die and no one knows why. It would be great if you would share with us any successes or failures you've had, if you have tried to raise horeseshoe crabs.
     The people at the Aquatice Resource Education Center in Smyrna, Delaware said there will be a workshop "Horseshoe Crabs in the Classroom"  given at Bombay Hook Wild Life Refuge on Wednesday,  May 16, 2001 from 4:30-8:00 p.m. If you live in Delaware and are interested in rearing horseshoe crabs, you really should go to that workshop.
     What we have written here is a combination of the Del. Fish & Wildlife's directions and what we have done.

 Collecting the eggs
1. It is suggested that horseshoe crab eggs be collected in late May, June or early July at the high tide line. Eggs can be found along most Delaware Bay beaches from Woodland Beach to Lewes. We got our eggs from Pickering Beach the first Saturday in June.
2. To find eggs you use your hands and dig down (gently) in the the sand at the high tide line. The eggs are light green and about 1-2mm (about the size of a beebe). They are usually in clumps just below the surface of the sand.
3. Put about one tablespoon of eggs in a bucket with enough sand to form a thin layer on the bottom of your tank.
4. Add enough clean bay water from where you are collecting to fill the container you are going to use to rear the crabs. If you are not going to be able to put the eggs in that container within one hour, you must aerate the water until you can.
Setting Up the Rearing Tank
1. Once you get the eggs to where you are going to rear them, gently pour the water, sand, and eggs (in that order) into the rearing pan or dishpan or aquarium (2-5 gallon capacity) or whatever you are going to use. We have ours in two different kinds of tanks.
    
2. Use a net to filter out any detritus or other unwanted material from the sand and water.
3. Before preparing and adding any mixed salt water, check the temperature and salinity of the bay water you brought home. Use a hydrometer to check the salinity.
    
4. Prepare a container of salt water, using one of the various aquaria salts available at a fish store, and match the temperature and salinity of the bay water. (A half-strength mix will get you to about 15-18 ppt which is what horseshoe crabs like.)
5. If the bay water is clean, use it undiluted in the rearing tank. If it is too murky, mix in some of the salt water you prepared. However, do not mix in more than 50% of what is already in the tank.
6. Adjust the air to provide a slow, steady stream of air bubbles.
7. Put the tank in an area where it gets at least 8 hours of indirect light a day and where the air temperature is at least 70 degrees. The eggs need warmth to hatch.
8. Depending on the amount of light and temperature, most of the eggs are supposed to hatch within one to four weeks. It took some of our eggs six - nine weeks to hatch. Below are pictures of some of our babies that are newly hatched on the left and one month old on the right.
    

Care, Feeding, and Other Details

What to feed: Once the horseshoe crab eggs start to hatch, begin feeding them  a combination of live and frozen baby brine shrimp. When you feed the frozen baby brine shrimp, break off a small chunk, melt it in a small amount of water and pour them ino the rearing tank. You can buy brine shrimp eggs and frozen brine shrimp at most pet or fish stores.
When to feed: Feed the crabs twice a week. Be sure not to overfeed or this will foul your water and kill the crabs. If a lot of shrimp detritus accumulates in the water the day after feeding, you probably are feeding them too much. Use an eye dropper and suction out the detritus and don't feed them as much.
Water changes: Do not change the water during hatching or before the first molt (when crabs shed their old shell). If you do, only change small amounts (no more than 1/3 tank volume). After the first molt, changing the water once a month should be adequate, but be sure to remember the keep the salinity and temperature constant.
Molting: As crabs molt and grow, increase the food accordingly. When the crabs first hatch they will be tailless. At this stage, they swim quite a bit and often become stuck at the water surface from the surface tension. Gently swirl the water to release them. Here are two of our babies that got stuck on the top. You can see the eggs on the bottom and the tracks of some of the babies that had been crawling around.

The baby crabs molt about six times their first year, growing up to 30% each molt. It is fun to save the molts to record their growth.
These are some of our first molts.

Thinning: As the crabs grow, it may be necessary to split them into two or more tanks or move them to a larger one. There should be no more than 50-60 first molt crabs per 2 gallon tank.
Release: The horseshoe crab young should be released back to the bay where you got the eggs sometime during the next summer. To carry the crabs to the site, carefully pour the crabs and water into a bucket or water tight container with lid. (If you have to travel more than two hours you must also aerate them.) When you get there, pour the baby crabs gently into the water as far out into the bay from the surf line as safely as you can.


back to index