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Greater Seattle Aquarium Society

Spawning the Japanese Marsh Shrimp

by Heather Canderlaria
May 1999

Here in Seattle, it seems that I am not the only person who has started a very nice collection of the recently famous Yamato-numa-ebi ---directly translated as the Japanese marsh shrimp, and occasionally known as the algae eating shrimp, or the Amano shrimp.

It appears that the animals currently sold by the name AES (Algae eating shrimp) are under the scientific name Caridina japonica, but I haven’t really been able to find much information about distinguishing freshwater shrimp species. Until proven otherwise though, I will be calling this little creature by that name.

Why should the scientific name be important? well, it will be very helpful in communicating with other people in other countries where the common name might be different, and I have been trying very hard to track down information about this animal because I have decided to try breeding it.

I don’t know if I’ll be successful in getting them to spawn, but I do know that I can now raise baby shrimps from eggs carried under the parents tail (presumably the female).

I’ve been able to purchase, from a wholesaler, egg-carrying shrimp which had spawned (released and fertilized eggs) prior to my receiving them. These egg carrying shrimp were then cared for until they released their hatching eggs. I’ve been able to raise 8 of the young shrimp, to the age of 35 days (and counting). These shrimp currently range between 4-8mm in size and look and behave exactly like the adults.

The first time I attempted to raise baby shrimp, they were released as the parent shed its exoskeleton and they were very tiny, free floating larva. They only lived about 7 days. In those 7 days they did grow, however they remained free floating larva. They never reached the phase where they would crawl along a surface.

From this initial experiment, I guessed that there was probably some sort of mineral supplement that I would have to add to the water. I guessed that for a shrimp to grow, it would need to be shedding its exoskeleton and forming a new one. In order to form a new shell, the shrimp would of course need the materials with which to do so... minerals.

I did a little research on freshwater shrimp, and found out that most of them are actually from brackish areas. This makes sense, in that the majority of the animals known as shrimps come from salt water. That is probably where shrimp first evolved. Some of them would probably then have migrated up streams, into brackish or freshwater areas.

Guessing that they would be biologically similar to their saltwater cousins, and with a hint from a diagram I found at a japanese web-site, I knew that the minerals they would need in order to form their shells would more than likely be found in sea salt.

When I purchased a shrimp carrying eggs early in February, I started adding sea salt to the water. I started off by adding 2 tsp. per gallon to the rearing tank. This was a 10 gallon tank with a sponge filter and lots of java moss and hornwort. There was also one small crypt growing in a one inch bed of mid-size dark gravel and a handful of crushed coral. In this tank I had a breeding trap filled with java moss, which is where I put the parent shrimp so that I could keep a close eye on it and see when the eggs had been released.

day 1: When the shrimp was first purchased, the eggs were about the size of its eyes. The shrimps coloring was unusually dark, and almost blue-black. It was about 1 inch in length and seemed to be carrying somewhere between 18-30 eggs.

day 2: After one day in the salted water, there were some very dramatic changes. The eggs seemed to have become more ovoid in shape, and the adult was still very dark in color, but much closer to a red color than the day before. I added more salt bringing it up to a total of 3 tsp. per gallon.

day 3: The shape of the eggs seemed to be less regular.

day 4: The eggs were now noticeably larger than the parents eyes, and possibly showing signs of the shrimp inside of them (possible eyes seen inside the eggs).

day 5: The eggs were released in the parents shed, one fuzzy egg was left behind on the old exoskeleton. The baby shrimp were fully formed! they could be seen clinging to the java moss within the breeding trap, and appeared to be about 2.5mm in length. I removed the parent shrimp, and started feeding the babies. I fed them a variety of foods; powdered krill, baby brine shrimp, powdered fry food, powdered Serra O-nips, and a product sold as a brine shrimp enhancement food (to gut load brine shrimp before feeding them to other fish) called Omega 3.

day 6: I was able to find 5 fry in the breeding trap.

day 7: I was able to find 3 fry in the breeding trap. The shrimps antennae seemed disproportionately long, possibly longer than their bodies, but it is hard to say because they were so small. I could only really see the antennae as movement of food and debris in the water, as the shrimp moved the antennae about in search of food.

day 8: I was able to find 6 fry, as I carefully siphoned out excess food from the bottom of the breeding trap.

day 9-10: I was able to find 4 live fry in the breeding trap, and I found the first dead ones. A total of nine dead shrimp were found. I was able to measure them and confirm a size of about 3mm body, and an additional 3mm length in the antennae. I added another 10tsp. of salt to the tank... After this, my estimate of the total salt content would be at about 4-5 tsp. per gallon (based on water changes, evaporation and possible addition of salt when adding in baby brine shrimp).

day 11: I was able to find 3 fry in the breeding trap. I found the first off-cast shell, it was the same size as the dead shrimp from day 9.

days 12-20: I was always able to find at least two fry in the breeding trap. There was no noticeable growth in this time.

day 21: I was able to find only 1 living fry in the breeding trap, and one dead one.

day 22: I released the final remaining shrimp from the breeding trap into the main tank, and started to look in the main tank for additional shrimp which escaped from the breeding trap (there was nothing really keeping them in the breeding trap, they could have escaped any time but I believe that most of them did not because of the lack of hiding areas between the java moss inside the trap, and the other vegetation on the bottom of the main tank). I was only able to find one additional shrimp in the main tank, and it was about 6mm (significantly larger than the one from the breeding trap). I suspect it was able to grow larger due to its access to more food in the form of dead/rotting hornwort on the bottom of the main tank. The Java moss in the breeding trap did not seem to be affected as adversely as the hornwort was. I suspect the high salt level caused some of the hornwort to die-off.

day 23: A total of 8 shrimp remain. Water temperature is 70F, pH 8.6, KH 4-5, and nitrates > 140 ppm. The shrimp are moved from the 10 gallon rearing tank into a smaller tank which has a bare bottom. I will be bringing the salt content down, and trying to reduce the nitrates by better cleaning of the bottom.

day 35: I still have 8 shrimp, and have seen at least one off-cast shell indicating that they are still growing. They are currently 5-8mm in size and I will now be bringing the salt content in their water down, so I can move them into a larger community tank (a planted 60 gallon tank holding other shrimp, Endler’s live bearers and a couple of Borneo sucker-mouths).

Based on this most recent experience in raising baby shrimp, I’ve been a little less sure of exactly which shrimp I’ve been dealing with.

The first time I attempted to raise what I thought was baby C. japonica, they hatched and were tiny free-floating larva. This most recent time, they were actually little crawling shrimp when they hatched. Were they really the same species? Maybe so, maybe not.

They could have been the same species, but hatched in two different environments very similar to the way brine shrimp will either give birth to live young, or young in an encapsulated cyst form (brine shrimp eggs). The brine shrimp will create cysts when the environment becomes unsuitable, in the hopes that the dormant young will live through whatever ecological threat might be occurring which could possibly wipe out all living non-encysted animals.

There is a possibility that the young shrimp which hatched as free-floating larva, did so because of the lack of salt in the water. If the young hatched high up in a freshwater stream flowing towards the ocean, the free floating young would then be pulled downstream towards the ocean and the vital minerals they would need in order to grow. On the other hand if there was already salt present in the water, maybe the eggs were actually able to somehow absorb the minerals to help give the young shrimp a head-start. This seems to be the only reasonable explanation as to why the already formed eggs could actually grow in size, as they seemed to do after the addition of salt to the water.

I am the first to admit that I am still baffled as to how to distinguish a male from a female shrimp. I have been staring at these things for many hours, of many days, and I do see some individual differences, but I couldn’t say with any certainty whether these traits are sexual dimorphism or not.

They seem to range in their colors, and some of the smaller ones have been observed displaying a beautiful dark reddish-brown color with an almost white stripe down the center of their back-side, and occasionally a cross stripe about half-way down their tail. The larger ones never seem to get this vivid in their color.

Another difference I’ve noticed, is in the structure of the face of the shrimp. The smaller more vividly colored ones seem

to have a more pronounced shell ridge between their eyes.

A few last observations about raising these baby shrimp would be in regards to their rearing tank. I really do think that the partially decaying hornwort was a valuable nutritional supplement, whereas the java moss seemed to grow with no die-off problem in the salted water. I think if I were to attempt to raise another batch of these shrimp, I would dispense with the breeding trap, load the tank with hornwort and just accept the fact that the shrimp will be very hard to find in the tank during the first month or so. I would not feed them the brine shrimp, or the powdered krill, and would instead rely on the hornwort, Sera O-nips and just a bit of the Omega 3. The Omega 3 would always cause a flurry of activity in the shrimp when it was added to the water and I would guess that it was a very attractive food to them. The Sera brand O-nips seem to be the food that the adult shrimps prefer.

Next I will be trying to get them to actually spawn, and I will be trying to do this by increasing the salt content in their water, and maybe playing around with the temperature a bit.

Hopefully another article outlining spawning of this animal will be written soon!

Postscript: As this article went to print (85 days) I have seen at least 3 of the shrimp which have been moved to my large community tank. The largest ones are over 15mm.

The marsh shrimp life cycle (adapted from