Gonodactylus
11/15/2010, 11:48 AM
It is difficult, but not impossible to culture Neogonodactylus wennerae and probably a few other gonodactylids (I have bred G. chiragra.) I can offer a few pointers.
1. Keeping a male and female together. Normally this is not a good idea. Competition for cavities and cannibalism during a molt can lead to one animal killing the other. However, if you use a large aquarium (at least a 35 gal) with lots of suitable cavities of different sizes so that animals can occupy the best defensible cavity for their size, a male and a female can coexist for some time. In fact, I have shown that males and females will not fight for at least a month after they have paired (see below). The key here is the animals have to be able to hide in and defend a suitable cavity and have somewhere to escape to. In the typical stomatopod aquarium there are not enough such cavities.
2. When to mate a male and a female. Let's say you obtain a male and female of breeding size (at least 40 mm for N. wennerae - it is better if the male is slightly bigger). The best time to try to mate them is when the female is receptive. This is the only time that she will pair with the male. You can tell if a female is receptive by looking at her cement glands. These are glands that can be seen through the ventral thoracic sternites. They produce the cement that hold the eggs together in a mass. When the female is ready to lay eggs, the cement glands become white and engorged and are very easy to see if you look at the ventral side of the animal. If you put a female and a male together at this time, they will usual occupy a burrow together although the male still may have to fight his way into the females burrow (a way the females "test" a male. It is better to introduce the female to a male occupying a cavity since males allow females in without a fight.
3. How long will they pair? The pair will remain in the cavity for at most a few days. During this time the male defends the cavity and the female from other males; the female fights off other females. When the female is ready to lay eggs - in the field usually on the full moon - she signals the male using a special display and he leaves. She then lays her eggs and forms them into a ball using the cement from the cement glands. If the male doesn't leave, she may become aggressive and try to evict him. The male then finds another cavity. If one is not available, or you don't remove him, the former pair could become aggressive. In the field I've seen males occupy cavities in the same rock as their former mate.
4. How long will the female brood her eggs? At 25 C, the eggs will take 3 weeks to hatch. The female cleans and aerates them during this time. She usually does not feed and is very aggressive in their defense. As I said above, the male will not attempt to evict his former mate during this time although he will fight with other females with eggs. Recognition of former mates is via odour. Should a female be evicted from her cavity, she can take her egg mass with her although it is unlikely that they will survive.
5. How long do larvae remain with the female in her cavity? When the larvae hatch, they are thigmotaxic and photo negative forming a mass in the bottom of the cavity. The female remains in the cavity with them. If she is evicted, the larvae are left behind. The larvae will live off of stores of yolk and will molt twice. After a week, they molt a third time, become photopositive and at first light swim out of the cavity and up into the plankton. They have exhausted their yolk supply and must begin feeding on small zooplankton almost immediately. At this point the mother begins feeding and will probably molt the following month.
6. My tank is full of larval stomatopods - what do I do now? Since the larvae are photopositive, you will probably notice them the morning that they leave the cavity swimming at the surface or on the side of the tank facing a window. If you do nothing, they will be dead in two to three days. They will NOT survive in the aquarium and fears of aquarists that stomatopods will breed in their tank are unfounded. If you want to try to rear them, collect them with a net or better yet, use a flashlight to attract them to the side of the tank and suck them up using a clean turkey baster. This is the best way to handle larvae. It produces less damage and you can be quite precise in moving them around. The larvae have several spines plus raptorial appendages that can get tangled in a net. Just make sure the baster is clean (stomatopods don't like turkey drippings!). Also, don't wash the baster in soap. The soap film that will adhere to the plastic is lethal. This is true for the containers that will house them as well. Soap and stomatopods do not mix and it is not allowed in my lab.
7. I've sucked up a bunch of larvae. Now what? If you want to rear N. wennerae larvae, they must be housed individually. They are armed with raptorial appendages and can injure one another either during cannibalistic attempts or chance aggressive encounters. I use 5-8 oz. plastic cups, preferably not transparent. They should be clean (no soap) and rinsed first in very hot water, then in sea water. Place one larva per cup. Manning and Provenzano, the first people to rear N. wennerae, placed the cups on gentle shaker tables to maintain some stirring and keep the prey in suspension, but Morgan and Goy and I have found this unnecessary as long as the water is changed daily. Temperature should be around 25 – 27 C. (There is a trade-off here. At higher temperatures development is more rapid and you will have to care for the larvae fewer days, but fouling of the water in the cups is faster and may require more frequent changes.)
8. How do I care for my larvae? The water must be changed frequently, preferably daily. Also, I find that using artificial sea water, not natural sea water or water from the aquarium, works best. The water in the cups is stagnant and organic matter in aquarium or natural water fouls more quickly. Here, being handy with the turkey baster is important. Gently suck up the larva and transfer it to a freshly rinsed and filled cup. Transfer as little of the old water as possible. With a clear glass baster you can usually see the larva in the water column and squeeze out excess water until there are just a few drops at the tip. This is a fairly time consuming process and will limit the number of larvae you can maintain. I find that it takes about half a minute per cup.
9. What do I feed the larvae? This is probably the trickiest part of rearing stomatopod larvae and it requires some planning. You can’t simply decide to rear them the morning they appear in you aquarium since they require feeding using LIVE prey from day one. The first week I feed copepods, rotifers, and Artemia nauplii gut loaded or soaked in a supplement such as Selcon. As they stomatopod larvae grow, you can move up to larger copepods and small brine shrimp (gut loaded and enriched). When the larvae first become free swimming, they will be a couple of millimeters long. Just before they settle, they will be about 6-7 mm. Prey should not be more than half the length of the stomatopod.
10. How much and how often do I feed my larvae? I feed daily (immediately after the water change) and add a lot of prey – probably 20 – 50 per cup per day. The higher the density of prey, the greater is the chance that the stomatopod larvae will encounter and eat them. This is where culturing prey (rotifers, copepods, Artemia) is important. I won’t go into culturing zooplankton here since there are lots of good resources on the web and in books and aquarium magazines. Just be ready to provide lots of food even though the stomatopod larvae will only take a few prey a day. Also, remember that as they swim in the cups, the prey are burning energy and using up nutrients, so resist the temptation to re-use those that are not eaten (although the remaining live prey can be placed back into their original culture medium). They are losing their nutritional value the longer they are in the cups and are not feeding.
11. How long to the larvae remain in the plankton? This varies with the species of stomatopod, but most gonodactylids including N. wennerae that I have studied have four pelagic stages and are in the plankton for about a month. N. wennerae seems to be somewhat plastic in this respect and may molt one extra time to stay in the water column longer if conditions are not suitable for settlement. I have found that when the larvae are nearing the time that they will settle, adding a thin layer of gravel to the bottom of the cup promotes molting to the post larval stage and settlement. However, this also makes them more difficult to clean and the transparent post larvae can be difficult to find in the gravel.
12. My larvae have molted to post larvae and have settled. Now what? Larvae molt to the post larval stage while still in the water column, settle, and remain transparent for four or five days. However, they behave like adults, living in cracks and crevices or tiny cavities and actively hunt and capture prey. They will also take dead prey such as commercial Cyclops based food. (I use live enriched Artemia and amphipods along with Cyclops-eeze.) The postlarvae will molt to juvenile adults in 10-14 days.
13. How long before the life cycle is complete and my juvenile N. wennerae begin breeding? This is not a quick life cycle. The juveniles will molt every 2 to 4 weeks growing about 10% in length each molt for the first six month; then the molting rate and growth will slow. In the laboratory, size of first reproduction is about 36 mm total length. Age at first reproduction is from 18 to 24 months, but can vary because of temperature and diet. Other species such as Gonodactylus chiragra take at least twice as long.
14. Is it worth it? It is good to say you have done it (once), but unless you have a good reason to do it such as describing the growth stages, it is a lot of work and the survival rate is very low – often less than 10%. Personally, I wouldn’t attempt it again. It is easier for me to go into the field and collect juveniles. In Panama, N. wennerae recruit every month (new moon) and we could collect dozens in an afternoon by breaking up small pieces of LR. On Lizard Island during spring recruitments, G. smithii postlarvae (pre-settlement) are attracted to light at night and we can collect literally hundreds in an hour.
Bottom line, culturing N. wennerae is possible, but it takes years, a lot of work, and probably is not worth the effort. Other stomatopods with larvae that spend even longer in the plankton are even more problematic.
1. Keeping a male and female together. Normally this is not a good idea. Competition for cavities and cannibalism during a molt can lead to one animal killing the other. However, if you use a large aquarium (at least a 35 gal) with lots of suitable cavities of different sizes so that animals can occupy the best defensible cavity for their size, a male and a female can coexist for some time. In fact, I have shown that males and females will not fight for at least a month after they have paired (see below). The key here is the animals have to be able to hide in and defend a suitable cavity and have somewhere to escape to. In the typical stomatopod aquarium there are not enough such cavities.
2. When to mate a male and a female. Let's say you obtain a male and female of breeding size (at least 40 mm for N. wennerae - it is better if the male is slightly bigger). The best time to try to mate them is when the female is receptive. This is the only time that she will pair with the male. You can tell if a female is receptive by looking at her cement glands. These are glands that can be seen through the ventral thoracic sternites. They produce the cement that hold the eggs together in a mass. When the female is ready to lay eggs, the cement glands become white and engorged and are very easy to see if you look at the ventral side of the animal. If you put a female and a male together at this time, they will usual occupy a burrow together although the male still may have to fight his way into the females burrow (a way the females "test" a male. It is better to introduce the female to a male occupying a cavity since males allow females in without a fight.
3. How long will they pair? The pair will remain in the cavity for at most a few days. During this time the male defends the cavity and the female from other males; the female fights off other females. When the female is ready to lay eggs - in the field usually on the full moon - she signals the male using a special display and he leaves. She then lays her eggs and forms them into a ball using the cement from the cement glands. If the male doesn't leave, she may become aggressive and try to evict him. The male then finds another cavity. If one is not available, or you don't remove him, the former pair could become aggressive. In the field I've seen males occupy cavities in the same rock as their former mate.
4. How long will the female brood her eggs? At 25 C, the eggs will take 3 weeks to hatch. The female cleans and aerates them during this time. She usually does not feed and is very aggressive in their defense. As I said above, the male will not attempt to evict his former mate during this time although he will fight with other females with eggs. Recognition of former mates is via odour. Should a female be evicted from her cavity, she can take her egg mass with her although it is unlikely that they will survive.
5. How long do larvae remain with the female in her cavity? When the larvae hatch, they are thigmotaxic and photo negative forming a mass in the bottom of the cavity. The female remains in the cavity with them. If she is evicted, the larvae are left behind. The larvae will live off of stores of yolk and will molt twice. After a week, they molt a third time, become photopositive and at first light swim out of the cavity and up into the plankton. They have exhausted their yolk supply and must begin feeding on small zooplankton almost immediately. At this point the mother begins feeding and will probably molt the following month.
6. My tank is full of larval stomatopods - what do I do now? Since the larvae are photopositive, you will probably notice them the morning that they leave the cavity swimming at the surface or on the side of the tank facing a window. If you do nothing, they will be dead in two to three days. They will NOT survive in the aquarium and fears of aquarists that stomatopods will breed in their tank are unfounded. If you want to try to rear them, collect them with a net or better yet, use a flashlight to attract them to the side of the tank and suck them up using a clean turkey baster. This is the best way to handle larvae. It produces less damage and you can be quite precise in moving them around. The larvae have several spines plus raptorial appendages that can get tangled in a net. Just make sure the baster is clean (stomatopods don't like turkey drippings!). Also, don't wash the baster in soap. The soap film that will adhere to the plastic is lethal. This is true for the containers that will house them as well. Soap and stomatopods do not mix and it is not allowed in my lab.
7. I've sucked up a bunch of larvae. Now what? If you want to rear N. wennerae larvae, they must be housed individually. They are armed with raptorial appendages and can injure one another either during cannibalistic attempts or chance aggressive encounters. I use 5-8 oz. plastic cups, preferably not transparent. They should be clean (no soap) and rinsed first in very hot water, then in sea water. Place one larva per cup. Manning and Provenzano, the first people to rear N. wennerae, placed the cups on gentle shaker tables to maintain some stirring and keep the prey in suspension, but Morgan and Goy and I have found this unnecessary as long as the water is changed daily. Temperature should be around 25 – 27 C. (There is a trade-off here. At higher temperatures development is more rapid and you will have to care for the larvae fewer days, but fouling of the water in the cups is faster and may require more frequent changes.)
8. How do I care for my larvae? The water must be changed frequently, preferably daily. Also, I find that using artificial sea water, not natural sea water or water from the aquarium, works best. The water in the cups is stagnant and organic matter in aquarium or natural water fouls more quickly. Here, being handy with the turkey baster is important. Gently suck up the larva and transfer it to a freshly rinsed and filled cup. Transfer as little of the old water as possible. With a clear glass baster you can usually see the larva in the water column and squeeze out excess water until there are just a few drops at the tip. This is a fairly time consuming process and will limit the number of larvae you can maintain. I find that it takes about half a minute per cup.
9. What do I feed the larvae? This is probably the trickiest part of rearing stomatopod larvae and it requires some planning. You can’t simply decide to rear them the morning they appear in you aquarium since they require feeding using LIVE prey from day one. The first week I feed copepods, rotifers, and Artemia nauplii gut loaded or soaked in a supplement such as Selcon. As they stomatopod larvae grow, you can move up to larger copepods and small brine shrimp (gut loaded and enriched). When the larvae first become free swimming, they will be a couple of millimeters long. Just before they settle, they will be about 6-7 mm. Prey should not be more than half the length of the stomatopod.
10. How much and how often do I feed my larvae? I feed daily (immediately after the water change) and add a lot of prey – probably 20 – 50 per cup per day. The higher the density of prey, the greater is the chance that the stomatopod larvae will encounter and eat them. This is where culturing prey (rotifers, copepods, Artemia) is important. I won’t go into culturing zooplankton here since there are lots of good resources on the web and in books and aquarium magazines. Just be ready to provide lots of food even though the stomatopod larvae will only take a few prey a day. Also, remember that as they swim in the cups, the prey are burning energy and using up nutrients, so resist the temptation to re-use those that are not eaten (although the remaining live prey can be placed back into their original culture medium). They are losing their nutritional value the longer they are in the cups and are not feeding.
11. How long to the larvae remain in the plankton? This varies with the species of stomatopod, but most gonodactylids including N. wennerae that I have studied have four pelagic stages and are in the plankton for about a month. N. wennerae seems to be somewhat plastic in this respect and may molt one extra time to stay in the water column longer if conditions are not suitable for settlement. I have found that when the larvae are nearing the time that they will settle, adding a thin layer of gravel to the bottom of the cup promotes molting to the post larval stage and settlement. However, this also makes them more difficult to clean and the transparent post larvae can be difficult to find in the gravel.
12. My larvae have molted to post larvae and have settled. Now what? Larvae molt to the post larval stage while still in the water column, settle, and remain transparent for four or five days. However, they behave like adults, living in cracks and crevices or tiny cavities and actively hunt and capture prey. They will also take dead prey such as commercial Cyclops based food. (I use live enriched Artemia and amphipods along with Cyclops-eeze.) The postlarvae will molt to juvenile adults in 10-14 days.
13. How long before the life cycle is complete and my juvenile N. wennerae begin breeding? This is not a quick life cycle. The juveniles will molt every 2 to 4 weeks growing about 10% in length each molt for the first six month; then the molting rate and growth will slow. In the laboratory, size of first reproduction is about 36 mm total length. Age at first reproduction is from 18 to 24 months, but can vary because of temperature and diet. Other species such as Gonodactylus chiragra take at least twice as long.
14. Is it worth it? It is good to say you have done it (once), but unless you have a good reason to do it such as describing the growth stages, it is a lot of work and the survival rate is very low – often less than 10%. Personally, I wouldn’t attempt it again. It is easier for me to go into the field and collect juveniles. In Panama, N. wennerae recruit every month (new moon) and we could collect dozens in an afternoon by breaking up small pieces of LR. On Lizard Island during spring recruitments, G. smithii postlarvae (pre-settlement) are attracted to light at night and we can collect literally hundreds in an hour.
Bottom line, culturing N. wennerae is possible, but it takes years, a lot of work, and probably is not worth the effort. Other stomatopods with larvae that spend even longer in the plankton are even more problematic.