Breeding of Red Clayed Manrovecrab/s (Sesarma sp.)

SatuVepsäläinen:

Breeding of red claved mangrove crabs from larvae to adult stage is said to be a very difficult if not an impossible task to do. This article written in a diary form describes how I managed to raise the larvae to small crabs.

THE BEGINNING

The beginning

Female mangrove crab with eggs

I took water and some bogwood from an already running tank to the breeding tank a week before the larvae hatched. At the same time I measured a recommended amount of salt (about 1 tablespoon per 1 litre) and checked the specific gravity of the water with a hydrometer (recommendation for gravity is 0.010 ppm). In the beginning I used aquamedic-salt, which is used for brackish water fishes and invertebrates. About a month later, I shifted to Reef Crystals-salt.

The breeding tank was a regular aquarium measuring 80 x 35 x 35 cm (length x width x height) with a volume of 98 litres. I placed a 2 cm thick layer of fine sand to the bottom of the tank. According to an article (Daniel Meier: Datz 4/1997) on the breeding of mangrove crabs it is beneficial for the larvae to have a tall water statue and airing with bubbles in the tank. Because of the dimensions of my tank I could not provide a tall water statue but I still managed to create two smaller statues of air bubbles. I placed two air hoses at the bottom of the tank, under the sand, mounted by rocks and bogwood which ensured that they would stay at the bottom. With rocks and bogwood I managed to create three air statues of big air bubbles.

Right temperature, nutrition and the amount of light are very important factors when raising the crab larvae. Calibration of the heater, placing a hatchery for artemia in the tank, adjusting the timer of the lamp and buying fluid food, were the first things to do.

Female mangrove crab carries the eggs under her wide tail brooding them approximately three weeks. Initially, the eggs are red but the colour changes during the brooding. When eggs are grey, the hatching is approaching.

When the colour of my female's eggs had turned grey, I moved her to the breeding tank, where she was provided with a piece of cork giving her an opportunity to climb above the water. The female hided most of the time behind the bogwood, on the top of the cork piece.

2 nd day

The larvae hatched the day before yesterday. After hatching I moved the female back to her own tank where she started to clean her tail.

I took the cover glasses off from the breeding tank because the water temperature had risen to 27 oC. There are thousands and thousands of both crab and artemia larvae in the tank. I decided to give also fluid artemia to the crab larvae. The fluid food (JBL Nobilfluid) is appropriate for very small fry. I mixed the fluid with a little amount of water and poured it into the aquarium.

I down regulated the air current with a help of the regulator in the air pump as well as a hose extortion in order to ease up the feeding of the crab larvae, since with a heavy current it is difficult for them to catch artemia.

There are three very weak air statues on both sides of the tank and the specific density of the water is 0.009 ppm (recommendation 0.010 ppm)

THE FIRST MOLT AND PROBLEMS WITH WATER

Zoea-larvs

I have given live artemia and fluid food to the crab larvae 4-5 times per day. It seems that they really can catch artemia. It is said, that crab larvae molt every third day. The first molt is therefore close.

The larvae swim energetically in the tank and even a little fighting seems to occur between them: today two of the larvae were tied up to each other and after a little struggle they managed to free themselves from each other.

5 th day

The larvae molted for the first time. The appearance of the larvae has changed a bit; for example, it is now easier to see the tail. It is very difficult to estimate the number of the larvae because there is so much artemia among them.

Today, I measured both the nitrate and nitrite content as well as the specific gravity of the water. There was 12,5 mg nitrate and 0.3 mg nitrite per litre. The specific gravity of the water was 0.010 (ppm). It seems that the salinity of the water has risen because of evaporation.

Either lack of beneficial bacteria in the water or the fluid food has caused the rise of nitrite. I guess that the first alternative is the right answer.

I try to reduce the nitrite content by changing water and decide to give fluid food only three times a day. The tail of the larvae is easy to distinguish now and they seem to be active in spite of the nitrite.

Both the artemia and the crab larvae seem to move towards the light. I noticed also that the crab larvae have gathered to a spot where the daylight shines from the window.

MEGALOPAS
Up

9th day

It seems that most of the larvae are still in the zoea-state. There are still plenty of them and their growth is noticeable. Yesterday, I changed some water and I have tried to reduce the nitrite content with a help of beneficial nitrate bacteria. The water temperature has risen from 26 to 27 oC although there are no cover glasses and I keep the windows open during daytime.

The last time I saw the larvae molting was yesterday (the 7th day from hatching). There was a little white clump under the larvae's tails and they freed themselves from it by struggling fiercely. These tiny white particles floated around the tank all the day. I think that this particle was probably a shell from a previous state of development and it came off during molting. The little ones are gathered in one corner at night and it is easy to view them with a pocket light.

10 th day

The first megalopas can be seen in the aquarium now. The molting seems to be very difficult for them and I can already see dead larvae on the bottom of the tank.

Megalopas and zoeas differ from each other in their outlook noticeably: megalopas are bigger and wider and you can distinguish the legs of the larvae. The megalopas are also lighter in colour than zoeas. One can distinguish megalopas from zoeas also by looking at how they swim. From my opinion, zoeas have a sort of "flying" style of swimming; they move quickly from place to place.

Megalopas swim in a more peaceful and stable way. The tails of the larvae are also different: the tail of the megalopas is thicker and straighter.

There is a large number of dead larvae on the bottom of the tank and I need to change water very often. Changing the water is very difficult because of the huge number of the crab larvae not to mention their tiny size. It is necessary to change water because of the elevated nitrite content. I try to change water in the following manner: First, I darken one side of a tank by putting a towel under the lamp. I then wait a moment so that the larvae will swim towards the light and flow water with a regular hose from tank to a bucket. After that, I "sieve out" the water: I collect the crab larvae with a help of a small hose into a smaller container and pour them back to the tank again.

I measure the specific gravity of new water with specific density meter and put one capsule of bacteria concentrate (Tetra bactozym) to the tank.

11 th day

Megalopa-larv

Megalopas were pictured today. The pictured larvae were about 1 mm in size and taking a picture was little bit difficult because the larvae grasped on the margins of the photographing aquarium with their claws. Some of the larvae are still in the zoea-state. I change water again.

13 th day

Most of the larvae died during molting and there are only about twenty-thirty megalopas alive now. It is hard to estimate how many are alive, because they stay most of the time at the bottom of the tank or hang on the glass or silicone.

17 th day

The larvae stay most of the time on different surfaces: on top of the bogwoods, on silicone joints and on the glass. From time to time they make short swimming spurts to catch artemia.

The larvae seem to seek food also from the glasses of the tank on which some fluid artemia has got stuck. The legs of the larvae start to get easier to distinguish.

21 th day

I give fluid food with live artemia to the megalopas two times a day and clean the bottom of the tank three times a week while changing water (about 40 % at a time). In spite of large water changes the nitrite content stays at the same level (0.3 mg/l). The legs of the larvae have grown and one can see them easily. The larvae do still perform short swims but stay most of the time on the bottom. It seems that they have difficulties with using their legs. Sometimes they walk with their back side up, sometimes they are upside down.

23 rd day

I moved some snails into the breeding tank from another aquarium. I hope, that they would eat leftovers, which have fallen to the bottom and algae which has grown on the surface of the bogwood.

26-28 th day

The larvae have gathered under a big bogwood. They do not swim anymore but walk on the surface of the sand. The shape of the larvae has changed: the body is now wider and more "crablike" than before.

Some of the larvae are in a "late megalopa-state"; they don't look like larvae anymore but they still are not tiny crabs yet.

31th day

A couple days ago at least 25 larvae seemed to be alive. Now it looks like that they have disappeared and I am little bit worried about them. Today, I saw one little crab walking along the bogwood.

35 th day

I am afraid that the larvae are not going to survive. The transition phase from a larvae state into a crab seems to be very difficult and I have seen the little crabs only on a rare basis.

THE LITTLE CRABS
Up

37th day

I changed water again and lifted one piece of bogwood to suck the dirt under it. I saw movement on the surface of the wood and got very surprised when I saw two little crabs walking on the surface of the wood. I could not believe my eyes. They were approximately 2-3 mm in size and they were brown just like they parents. They moved very fast and when I took pictures of them one crab almost succeeded to escape from the photographing aquarium.

38th day

The little crabs molted for the first time and I can see many empty shells on the surface of the wood. I put cork in the tank so that the crabs can climb and walk above the water surface.

50th day

There are at least 10 tiny crabs in the tank, maybe more. They molt at different times, approximately every 7 to 10 th day. Two days ago three crabs molted during the same day. The largest ones are approximately 3,5 mm wide (measured without legs) now the smallest being only 1,5 mm. Most of them are 3mm in size. I have seen only two very small crabs.

I took the artemia hatchery away from the tank about a week ago because the small crabs are not able to catch artemia anymore.

I have given them some flake food two times a day as well as small granulates or frozen bloodworms. I change 40% of the water twice per week now, and suck the dirt from the bottom. There is still nitrite in the water. Salinity of the water is the same as before.

140th day

There are approximately 25 - 30 little crabs in the tank. The biggest ones are now approximately 1,0 cm in size and it is possible to see the differences between the sexes. There is no salt in the water anymore. I give flakes, granulates, bloodworms and vegetables to the little ones and I have noticed, that they love peas!

Born in Finland



		*From thousands little points to Dekapods - Breeding of Red Clayed Manrovecrab/s (Sesarma* sp.) SatuVepsäläinen: Breeding of red claved mangrove crabs from larvae to adult stage is said to be a very difficult if not an impossible task to do. This article written in a diary form describes how I managed to raise the larvae to small crabs. THE BEGINNING The beginning Female mangrove crab with eggs I took water and some bogwood from an already running tank to the breeding tank a week before the larvae hatched. At the same time I measured a recommended amount of salt (about 1 tablespoon per 1 litre) and checked the specific gravity of the water with a hydrometer (recommendation for gravity is 0.010 ppm). In the beginning I used aquamedic-salt, which is used for brackish water fishes and invertebrates. About a month later, I shifted to Reef Crystals-salt. The breeding tank was a regular aquarium measuring 80 x 35 x 35 cm (length x width x height) with a volume of 98 litres. I placed a 2 cm thick layer of fine sand to the bottom of the tank. According to an article (Daniel Meier: Datz 4/1997) on the breeding of mangrove crabs it is beneficial for the larvae to have a tall water statue and airing with bubbles in the tank. Because of the dimensions of my tank I could not provide a tall water statue but I still managed to create two smaller statues of air bubbles. I placed two air hoses at the bottom of the tank, under the sand, mounted by rocks and bogwood which ensured that they would stay at the bottom. With rocks and bogwood I managed to create three air statues of big air bubbles. Right temperature, nutrition and the amount of light are very important factors when raising the crab larvae. Calibration of the heater, placing a hatchery for artemia in the tank, adjusting the timer of the lamp and buying fluid food, were the first things to do. Female mangrove crab carries the eggs under her wide tail brooding them approximately three weeks. Initially, the eggs are red but the colour changes during the brooding. When eggs are grey, the hatching is approaching. When the colour of my female's eggs had turned grey, I moved her to the breeding tank, where she was provided with a piece of cork giving her an opportunity to climb above the water. The female hided most of the time behind the bogwood, on the top of the cork piece. 2 nd day** The larvae hatched the day before yesterday. After hatching I moved the female back to her own tank where she started to clean her tail. I took the cover glasses off from the breeding tank because the water temperature had risen to 27 oC. There are thousands and thousands of both crab and artemia larvae in the tank. I decided to give also fluid artemia to the crab larvae. The fluid food (JBL Nobilfluid) is appropriate for very small fry. I mixed the fluid with a little amount of water and poured it into the aquarium. I down regulated the air current with a help of the regulator in the air pump as well as a hose extortion in order to ease up the feeding of the crab larvae, since with a heavy current it is difficult for them to catch artemia. There are three very weak air statues on both sides of the tank and the specific density of the water is 0.009 ppm (recommendation 0.010 ppm) THE FIRST MOLT AND PROBLEMS WITH WATER Zoea-larvs Up I have given live artemia and fluid food to the crab larvae 4-5 times per day. It seems that they really can catch artemia. It is said, that crab larvae molt every third day. The first molt is therefore close. The larvae swim energetically in the tank and even a little fighting seems to occur between them: today two of the larvae were tied up to each other and after a little struggle they managed to free themselves from each other. 5 th day The larvae molted for the first time. The appearance of the larvae has changed a bit; for example, it is now easier to see the tail. It is very difficult to estimate the number of the larvae because there is so much artemia among them. Today, I measured both the nitrate and nitrite content as well as the specific gravity of the water. There was 12,5 mg nitrate and 0.3 mg nitrite per litre. The specific gravity of the water was 0.010 (ppm). It seems that the salinity of the water has risen because of evaporation. Either lack of beneficial bacteria in the water or the fluid food has caused the rise of nitrite. I guess that the first alternative is the right answer. I try to reduce the nitrite content by changing water and decide to give fluid food only three times a day. The tail of the larvae is easy to distinguish now and they seem to be active in spite of the nitrite. Both the artemia and the crab larvae seem to move towards the light. I noticed also that the crab larvae have gathered to a spot where the daylight shines from the window. MEGALOPAS Up 9th day It seems that most of the larvae are still in the zoea-state. There are still plenty of them and their growth is noticeable. Yesterday, I changed some water and I have tried to reduce the nitrite content with a help of beneficial nitrate bacteria. The water temperature has risen from 26 to 27 oC although there are no cover glasses and I keep the windows open during daytime. The last time I saw the larvae molting was yesterday (the 7th day from hatching). There was a little white clump under the larvae's tails and they freed themselves from it by struggling fiercely. These tiny white particles floated around the tank all the day. I think that this particle was probably a shell from a previous state of development and it came off during molting. The little ones are gathered in one corner at night and it is easy to view them with a pocket light. 10 th day The first megalopas can be seen in the aquarium now. The molting seems to be very difficult for them and I can already see dead larvae on the bottom of the tank. Megalopas and zoeas differ from each other in their outlook noticeably: megalopas are bigger and wider and you can distinguish the legs of the larvae. The megalopas are also lighter in colour than zoeas. One can distinguish megalopas from zoeas also by looking at how they swim. From my opinion, zoeas have a sort of "flying" style of swimming; they move quickly from place to place. Megalopas swim in a more peaceful and stable way. The tails of the larvae are also different: the tail of the megalopas is thicker and straighter. There is a large number of dead larvae on the bottom of the tank and I need to change water very often. Changing the water is very difficult because of the huge number of the crab larvae not to mention their tiny size. It is necessary to change water because of the elevated nitrite content. I try to change water in the following manner: First, I darken one side of a tank by putting a towel under the lamp. I then wait a moment so that the larvae will swim towards the light and flow water with a regular hose from tank to a bucket. After that, I "sieve out" the water: I collect the crab larvae with a help of a small hose into a smaller container and pour them back to the tank again. I measure the specific gravity of new water with specific density meter and put one capsule of bacteria concentrate (Tetra bactozym) to the tank. 11 th day Megalopa-larv Megalopas were pictured today. The pictured larvae were about 1 mm in size and taking a picture was little bit difficult because the larvae grasped on the margins of the photographing aquarium with their claws. Some of the larvae are still in the zoea-state. I change water again. 13 th day Most of the larvae died during molting and there are only about twenty-thirty megalopas alive now. It is hard to estimate how many are alive, because they stay most of the time at the bottom of the tank or hang on the glass or silicone. 17 th day The larvae stay most of the time on different surfaces: on top of the bogwoods, on silicone joints and on the glass. From time to time they make short swimming spurts to catch artemia. The larvae seem to seek food also from the glasses of the tank on which some fluid artemia has got stuck. The legs of the larvae start to get easier to distinguish. 21 th day I give fluid food with live artemia to the megalopas two times a day and clean the bottom of the tank three times a week while changing water (about 40 % at a time). In spite of large water changes the nitrite content stays at the same level (0.3 mg/l). The legs of the larvae have grown and one can see them easily. The larvae do still perform short swims but stay most of the time on the bottom. It seems that they have difficulties with using their legs. Sometimes they walk with their back side up, sometimes they are upside down. 23 rd day I moved some snails into the breeding tank from another aquarium. I hope, that they would eat leftovers, which have fallen to the bottom and algae which has grown on the surface of the bogwood. 26-28 th day The larvae have gathered under a big bogwood. They do not swim anymore but walk on the surface of the sand. The shape of the larvae has changed: the body is now wider and more "crablike" than before. Some of the larvae are in a "late megalopa-state"; they don't look like larvae anymore but they still are not tiny crabs yet. 31th day A couple days ago at least 25 larvae seemed to be alive. Now it looks like that they have disappeared and I am little bit worried about them. Today, I saw one little crab walking along the bogwood. 35 th day I am afraid that the larvae are not going to survive. The transition phase from a larvae state into a crab seems to be very difficult and I have seen the little crabs only on a rare basis. THE LITTLE CRABS Up 37th day I changed water again and lifted one piece of bogwood to suck the dirt under it. I saw movement on the surface of the wood and got very surprised when I saw two little crabs walking on the surface of the wood. I could not believe my eyes. They were approximately 2-3 mm in size and they were brown just like they parents. They moved very fast and when I took pictures of them one crab almost succeeded to escape from the photographing aquarium. 38th day The little crabs molted for the first time and I can see many empty shells on the surface of the wood. I put cork in the tank so that the crabs can climb and walk above the water surface. 50th day There are at least 10 tiny crabs in the tank, maybe more. They molt at different times, approximately every 7 to 10 th day. Two days ago three crabs molted during the same day. The largest ones are approximately 3,5 mm wide (measured without legs) now the smallest being only 1,5 mm. Most of them are 3mm in size. I have seen only two very small crabs. I took the artemia hatchery away from the tank about a week ago because the small crabs are not able to catch artemia anymore. I have given them some flake food two times a day as well as small granulates or frozen bloodworms. I change 40% of the water twice per week now, and suck the dirt from the bottom. There is still nitrite in the water. Salinity of the water is the same as before. 140th day There are approximately 25 - 30 little crabs in the tank. The biggest ones are now approximately 1,0 cm in size and it is possible to see the differences between the sexes. There is no salt in the water anymore. I give flakes, granulates, bloodworms and vegetables to the little ones and I have noticed, that they love peas! Born in Finland Up