Breeding Red Mangrove Crab (Pseudosesarma sp.)

[Ollie Mengedoht]

Breeding report
Text: Monika Rademacher
Photos: Oliver Mengedoht
Translation: Ulrike Bauer

When we decided to try breeding our Pseudosesarma, which only works with brackish water, we were faced with the facts that we neither had any well-founded knowledge nor any experience of our own regarding brackish water aquaristics.

Our most forward goal for this breeding experiment was to make it as uncomplicated as possible, i.e. to make do without expensive equipment, encyclopaedic knowledge or complicated breeding conditions.
During the entire breeding process we didn't change water or measure any parameters in the breeding tank.
This might seem curious to some, but success has proven us right, the zoea larvae went through various stages of development and have grown to be little Pseudosesarmas over some weeks.

Breeding red mangrove crab (Pseudosesarma)

The female crab carries her eggs for a good three weeks.
The development from larva to fully developed miniature crab has taken 28 days during this breeding experiment.

First we separated a berried female as soon as her eggs had developed from brownish to a greyish color and started to get a rather "frayed" look.

The separation basin had a volume of 500ml and was equipped with a little aquarium sand and 300 ml of water. Moreover, the basin contained a holey limestone rock protruding from the water in order to provide the crab with access to land.



The water in this basin was half original water from the crab's aquaterrarium, half brackish water from the projected crab propagation basin. This had a salinity of 25 g sea salt per liter.
After a little less than 24 hours, the female released thousands of larvae. This process took around 20 hours.



The crab larvae were transferred to the propagation tank in batches. This tank had been running for five and a half weeks then. It was a 54 l standard tank with a 15W fluorescent tube. The substrate was a layer of white aquarium sand of 1.5 cm, the basin was filled with 40 l of brackish water with a salinity of 25 g sea salt per liter, the temperature was a constant 24 °C during the entire breeding process.

There was no filter. We aerated this tank by a Tetratec 100 air pump and an air ball.

When the larvae were transferred, the tank showed some algae, there was only a little muck, and since we had set up the tank in August we hadn't performed any water changes. We only replaced evaporated water with normal tap water.
We continued this during the entire development process from the larval stages to miniature crabs.



Other tank inhabitants were lots of Artemia of all developmental stages that were still there after the last, unsuccessful breeding experiment.

As our last attempt at breeding had failed, this time we had decided to change the breeding conditions by running the light for 24 hours.
We minimized the aeration during the night so only very little air got into the tank.

After the female crab had released the largest part of the larvae we put her back into her aquaterrarium with a few remaining eggs in her pouch.
One reason for re-transferring the female this quickly was that adult crabs don't really seem to do too well in brackish water for a longer period of time.
As during our first breeding attempt she seemed rather lethargic and weak after a certain time.
This might have resulted from releasing her larvae, however, the rather quick transferral from fresh to brackish water might also have played a role.

The propagation tank was teeming with zoean larvae now. At this early stage they have a rather round appearance, and under a magnifying glass we could clearly distinguish a nearly ball-shaped body with a tiny tail that was lying closely against the body.
The eyes could also be seen.





During the first 72 hours after hatching we fed them Liquizell (brine shrimp food) and powdered spirulina twice a day. During feeding time we disconnected the aeration so the larvae didn't have to fight the current while eating.

After 72 hours we widened their diet by Artemia nauplii from our hatchery and gave them one more meal per day. In order for the zoea larvae to find the nauplii fast we switched the light off and darkened the tank entirely. Just one corner was lit with a halogen spotlight.

Nauplii as well as the zoea larvae are phototactic. Therefore all the animals gathered in the cone of light, and the larval crabs could hunt down their food without wasting more energy than necessary.

In order to prevent the animals from being hurled about we also discontinued the aeration for about an hour when feeding. When this hour had elapsed, the standard light was switched on again and we resumed aeration.

We learned that the optimal time for observation was about 20 minutes after we had begun feeding, as then the most zoea larvae gathered in the cone of light near the tank bottom because the most nauplii had also gone there.



When five days had elapsed after hatching we could see the first molts. Many of the zoean had skin rests hanging from the ends of their little tails.
Some zoean even changed their bearing, they didn't press their tail so close to the body any more but moved it a little, holding it further away.



After eleven days the first few megalopae appeared. Their coloring is noticeably lighter than the zoea larvae's, and they seemed to be able to control their swimming better than the zoean, which swim rather jerkily. The megalopae held their tail differently from the zoean. Under a magnifying glass the first little legs could be distinguished.

The megalopae use their tail for steering, and we could also observe that they fought the zoean. Later on we could see that the megalopa larvae also fought and even cannibalized each other.



After sixteen days the megalopae had developed futher and we could distinguish the basic form of the back carapace. These larvae's legs were more pronounced, too.



During this stage of development the megalopae changed their behavior. They didn't stay close to the tank bottom any more but swam to higher regions, seemingly on purpose. Some of the megalopae started to sit on the glass sides for a little and grazed on the algae that had grown rather dense there during the last sixteen days. Moreover, the larvae walked on the ground more often, whereas we could describe their way of locomotion as a mixture of walking and hopping.



At this time we could perceive clearly that the crab larvae developed at different speeds. There were still zoean of various stages as well as several stages of megalopa larvae.

After 18 days we could see that those megalopae that moved on the ground were really walking. Seemingly the larvae at this stage have a kind of claws they actively use. The tails of some of them had shortened, and all of these larvae showed a clear segmentation on their tails (under a magnifying glass). During the further development the tail will be folded under the belly and form the pleon.



On the 20th day we finally could see the first "almost" crabs. They already had the form of miniature crabs, however, in contrast to fully developed crabs they had only six legs instead of eight.



In the meantime the claws were clearly distinguishable, the larvae were using them purposefully. Now we could also see the typical movements of crabs, as e.g. walking sideways. These far-developed megalopae showed a tiny tail but already started to fold it under their belly.

Now we changed the tank design by decreasing the water level by 1/3 and putting in a mangrove root. This had been soaked in salt water and was tied to a spaghetti stone. We did this in order to enable the further developed megalopae to leave the water. They mainly used the stone and the root as hiding-places.

Finally, after 28 days, we spied the first fully developed young crab in the propagation tank. The legs and claws were clearly segmented, the crab showed a brownish color on the carapace and the segment edges, all in all it was still pretty transparent. This crab was speckled, maybe this was a camouflage mechanism.





In the meantime five and a half months have elapsed since we've spotted the first young crab. From this breeding experiment we got 123 young mangrove crabs.

These animals' growth rates are directly related to how much room they have.
When the population is very dense they only grow very slowly, this is why we transferred them to three growing tanks a few wees ago.
Since then their growth has sped up, but they still differ strongly in size.

The largest specimens are three young crabs we had put into the parents' tank rather early.
These already have a carapace diameter of about one centimeter, whereas the largest crabs in the growing tanks have 0.7 cm of carapace diameter, the smalles measure only 0.3 cm.

Over several weeks the young crabs were gradually acclimatized to fresh water, however, there is still a small percentage of salt in the water of the growing tanks since the substrate and roots still give off a small amount of salt.
When transferring the crabs to the various tanks we started regular water changes (50% once a week) and only added fresh water.



Einen ausführlichen Nachzuchtbericht als PDF-Datei findet ihr hier
http://www.panzerwelten.de/d/100743-1/Krabbenzucht.pdf