Mating, reproduction and raising of African dwarf frogs
Text: Monika Rademacher
Photos: Oliver Mengedoht
Translation: Ulrike Bauer
In the last issue of Shrimp Online we gave a report about African dwarf frogs, which of course aren't invertebrates, but nevertheless interesting and rather uncommon aquarium inhabitants. As we announced back then, in this current issue we're dealing with the breeding of these adorable little leg-kickers. Even though the upbringing of the tadpoles is a little complicated you'll gain interesting insight into the metamorphosis of frogs by watching their development stages from the egg over the various tadpole stages to the fully developed young frog.
The most important prerequisite for successful breeding is, of course, bringing together adult animals of both sexes for a start and providing the necessary conditions for them to get ready to mate. This condition per se is met in dedicated tanks anyway, in social tanks mating occurs only very seldomly. In this case we recommend setting up a small mating tank.
As a rule, adult female dwarf clawed frogs have a more massive build, and with a head-trunk length of 4.5 cm they are a bit larger than the males, which grow to about 3.5 cm. The most decisive characteristic for distinguishing the sexes are, however, the postaxillary glands of the males, which can be found in the region behind the front legs.
In semiadult frogs these glands can be seen as slightly convex light-colored marks that start to grow when sexual maturity approaches and swell to wart-like pink bulges when the frogs become sexually active. When this activity ceases the glands shrink a little in diameter and thickness, yet they remain clearly visible.
The female frogs don't show any discoloration or swelling, they do not have postaxillary glands.
Other criteria that are regularly mentioned as e.g. the length of the tail remainder can give you vague clues but are no positive characteristics for definite distinction.
Courtship behaviour and mating
Male frogs announce their sexual activity by a stunted-sounding croak not short of persistency and insistence though. It can be very well compared to a raspy cricket chirp. During its courtship calls the male frog strikes a very peculiar pose. It practically stands on its hind legs with outstretched body in a 30° angle to the ground and waits there until a receptive female is lured there by the concert. Even though the calls are clearly audible you cannot make out any action in the frogs that would let you see how these sounds are produced. Terrestrial frogs croak with the help of vocal sacs, their aquatic relatives do not have any visible comparable organs.
Mating itself starts with copulative swimming, for which the male clutches the female's loin area. The male's head lies on the female's back between its pelvic bones. This clasp is called amplexus. Young adults have to practise this clutch at first; if they don't grasp their partner in the right way the female can free itself pretty quickly from the clumsy grip and the copulation is unsuccessful.
If both participants are in the right position they start copulative swimming for a long time during which they frequently cross the entire tank and also head for the surface together from time to time in order to breathe. After several hours of this preparative swimming the frogs change their movement pattern by turning around by 180 degrees so that their bellies point to the surface. Once in this position the female emits the eggs from her cloaca, and the male fecundates them at the same moment. Then the pair dives again and repeats that procedure some more times until all the eggs have been released to the surface and got fecundated, then the male loosens its grip and mating is over. This entire procedure can take from 12 to 28 hours, and we have even witnessed copulations that took longer than that.
If you want to raise the young frogs you'll first have to remove the spawn, as the adults will eat it within a few hours in the breeding tank.
There are different methods of raising African dwarf frogs; to me it was important to develop a method with which you can bring up a relatively large number of young frogs with as litte time and money involvement as possible. For all of you who'd like to try an easy-to-realize breeding set-up I'd like to present a description of one of ours.
Raising African dwarf frogs
Once you have removed the eggs from the adult tank you put them into a shallow bowl filled with 0.5 l of the adults' tank water. The eggs floating on the water surface resemble poppy seeds covered by a thin gelatinous layer.
Additionally, some plants should be put into the bowl, too. Very well suited are hornwort, frogbit and other small floating plants. The hatched tadpoles can be spotted more easily in colored, dark bowls. You can light and heat the container with a desk lamp, and you ought to make sure that the water's a constant 24 °C (75 °F).
After 24 to 36 hours the tadpoles hatch. At first they look like longish-oval disks about 1.5 mm in size, tapering at one end, of a beige to light brown color. They seem rather immobile, but react to direct touch or light shaking of the bowl with short twitching movements. You don't have to feed them at this stage. The tadpoles mostly stay on the bottom of the bowl, only a few will hang in the floating plants. Only 24 hours later you will perceive significant changes. Their length almost doubles, and their coloring changes to nearly black. You can easily spot a yolk bag in their belly region and a round head section as well as a strongly tapering tail. When stretched out they are about 2.5 to 3 mm in size. Some of the hatchlings can be found at the bowl's walls and in the floating plants, but most of them still lie on the ground. Please start feeding three times a day now, every 7 hours, with Liquizell starter food, and once a day you add some dissolved growth food. In the mornings and the evenings the tadpoles are transferred into a new bowl with 0.5 l of fresh water from the adult frogs' tank.
On the third day of their lives their form finally changes to the classical tadpole outline. They display a round head with a thin, pointy little tail. The tadpoles start swimming freely but also lie on the ground quite often. To direct touch or vibrations they no longer react with twitching, but show clear swimming movements. These sequences only last a few seconds until they've found another resting place. The food plan now widens to living Artemia naupliae fed once a day together with Liquizell, however, an active food intake cannot be perceived yet. Keep transferring the tadpoles into a new bowl with fresh tank water two hours after feeding. This is best done with a plastic pipet in order not to put the animals under additional stress by netting them. When you use the pipet the tadpoles are sucked in with a minimal water intake and then are put into their new bowl. During this procedure they seem neither hectic nor stiff.
On the following day, the tadpoles are distinctively larger and more agile. They swim close to the water surface, and their eyes are clearly visible. Due to their increasing activity they should now be transferred to a larger bowl. There the water level should not be over 3.5 to 4 cm. This provides for an optimal surface gas exchange. This water also has be replaced with fresh tank water twice a day. During the next days their looks will change by the day. Their color and body outline keep transforming bit by bit, and when they're ten days old they hardly resemble those little black balls of the first days.
During this stage they should be fed with Artemia naupliae in the mornings and evenings. Unfortunately some tadpoles might die even though the water hygiene is good and they're well-fed. Please remove dead tadpoles immediately from the bowl since they tend to grow fungus in no time. You will notice various stages of tadpole development in the bowl. However, this is no reason to worry but seems to be their nature. At this age you might even see light spots on some animals where their hind legs are going to be.
On the 14th day of their lives you can watch the little swimmers taking in air at the surface and then making bubbles under water, exhaling just like adult frogs.
At the age of 17 days the bowl seemed to get too small for our tadpoles at last, and the time had come to transfer the offspring to a growth tank. Back then I used a 54 l standard tank with scant planting in order to give the tadpoles a lot of swimming room and to avoid nooks and crannies where they could get caught. The water level was only 13.5 cm so they could still reach the surface without problems. We filtered the tank with a little HOB filter with a secured intake pipe, under whose water outlet we placed a large piece of filter sponge. The sense of this was to avoid any and all current in the tank, as the little tadpoles cannot fight any water flow at all; they would thus just waste energy unnecessarily. In order to maintain a constant growing temperature of 24 °C we also had to install a heater, which we covered with a thin slab of filter mat.
Due to the considerably larger water volume and the additional filtration the water changes that had been our daily task during the last two-and-a-half weeks could be ceased now. Weekly partial water changes of about 10 to 15% are enough to maintain a good water quality for the offspring.
You cannot transfer them to such a large tank without altering your feeding methods. If you just put the naupliae into the tank they would scatter according to the tank volume, and the tadpoles would need a lot of energy just looking and hunting for their staple. You can counter this, however, by turning off the tank lights while feeding and just lighting one corner of the tank with a clip-on lamp. Naupliae and tadpoles alike are quickly drawn to the light, and the tadpoles are virtually swimming in their food, which enables them to eat without wasting energy unnecessarily. The first animals will now grow light-colored limb appendages on the right and left side of their tail root.
Just a week later the little ones' diet amplifies again, you can offer them the first young daphniae, which they'll hunt down successfully. 48 hours later you can feed them fine frozen food for the first time. The tadpoles, now 26 days old, eat the Cyclops offered to them very well. During the next days you can observe the formation of the feet on the larger animals about 2 cm in size.
35 days after hatching the largest of the offspring grow their front legs, and only a few days later you can even discern the individual toes on them. During the following days the tadpoles' looks change and the animals get more and more frog-like. Their legs grow longer and stronger – and are applied more purposefully for swimming.
After 39 days they bear a striking resemblace to frogs, and they are learning to coordinate their front and hind legs. As before, the tadpoles' development stages differ a lot. On the 42nd day you can see animals with fully grown limbs side by side with some that haven't even started to grow them.
Finally, on the 44th day, the first animals start metamorphosing into a frog. First their tail shortens considerably and, in the course of the next 24 hours, it reduces by over 50% of its original length.
Another 24 hours later only a small rest reminds the onlooker that the young frog used to have a tail. Our first young frogs were swimming in the growth tank 46 days after hatching. 50 days after removing the spawn from the adults' tank the offspring that resulted from the raising procedure we've described counted 12 young frogs and 32 tadpoles, eight of which were metamorphosing, 6 had completely grown limbs and were shortly before metamorphosis, 15 had their hind legs, showing front leg growth, and 3 were growing their first pair of legs. All in all, we got 44 young frogs from the 63 eggs we had gathered.
Directly after metamorphosis the young frogs measure about one centimeter from head to tail root. Now naupliae do not offer enough nutrients to be the only staple any more, thus you should feed a variety of foods from now on. Young Artemia or living Daphnia, but also shredded frozen mosquito larvae or tiniest bits of earthworm ensure your froggies get a diversified and balanced nutrition.
It is not often the case that you can keep all the frogs you've raised yourself. They can be given away when they've reached about 2 cm from head to tail root. We gave away our frog offspring when they were about two-and-a-half to three months old.