Mike Edwardes: The Amphibiary: Hymenochirus

Hymenochirus species

(African dwarf frog)

Housing:

Generally speaking, these frogs are NOT suitable tankmates for fish. The only exceptions to this are a few small, gentle species of fish, but the frogs are almost always better off in a tank of their own. Entirely aquatic (although good at escaping from uncovered tanks!), they need still water. Any filtration must not create strong water currents. For the most part, I have kept these frogs in unfiltered, heavily planted tanks. These need not be large, 45x25x30cm (18x10x12") is fine, although of course the frogs will do better with more space. My current tank is 60x45x40cm (24x18x16") with 20cm (8") depth of water and houses 10 frogs:

Frog tank

If you prefer to use a filter instead of heavy planting, it should not create strong currents. Air-driven box or sponge filters are easier than power filters, especially in smaller tanks, but please don't blast your frogs. And no filter is a substitute for regular partial waterchanges, e.g. 10-15% per week, or 20-25% a fortnight.
Quite sociable, they seem to prefer to be kept in groups - you should allow at least 4 litres (1 US gallon) per frog, preferably more. Temperatures of 21-27°C (70-80°F) are preferred. In my experience, they are sensitive to cold, and I lost an entire group once when the temperature dipped to 19°C (66°F), so unless the room they are in is always comfortably warm, you'll need a submersible aquarium heater/thermostat.

Feeding:

These frogs will not take dried foods, but they will eat frozen bloodworms. However, this should be supplemented with live foods such as:

Generally, they should be fed every other day only as much food as they can eat in 15-30 minutes, although if a few Daphnia remain in the tank, this is not usually a problem. It is NOT a good idea to add more food than this - these frogs can and do overeat with fatal consequences.

Should you buy a dwarf frog?

Pros:

Interesting, active, diurnal frog.
Fairly easy to house, a 45x25x30cm (18x10x12") aquarium (or larger), is fine.
Relatively easy to breed if properly cared for.

Cons:

Quite a delicate frog, partly because of its small size. Not really a good first amphibian.
Accomplished escape artists - climb surprisingly well and squeeze through tiny gaps. Tanks must be tightly covered (e.g. where heater cables enter), but also well ventilated.
The status of these frogs in the wild is uncertain, but they are endangered. Fortunately, most specimens you are likely to encounter in the pet trade are captive-bred.

Difficulty Rating: 4/10

Not an ideal species if you've never kept an amphibian before. Quite delicate - thousands of these frogs die in the hands of novice amphibian keepers every year. If you're attracted to aquatic species, consider an Axolotyls or Xenopus first.

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Learn all you need to know about setting up the right kind of housing for your frog or toad - be it a terrestrial, aquatic or semiaquatic species. (Amazon.co.UK)

Breeding:

BEFORE YOU BREED YOUR FROGS, ASK YOUSELF:

What am I going to do with 100 frogs?
NEVER release captive-bred frogs, even if they are indigenous to the area - you could be spreading disease which could wipe out wild populations.
Don't ASSUME your local pet store will take them - have you asked?
Do I have the time/space to rear them?
Are you prepared to dedicate several months and some cash to this project?

If the answer to any of these questions is no and your frogs have bred, the simplest and most humane solution is to leave the eggs with the parents, who will eat the tadpoles. Seems cruel? This is the natural answer to overpopulation - NEVER flush frogs or eggs down the toilet!

These frogs are relatively easy to breed if properly cared for. To start with, you need (at least) one pair:

Male Hymenochirus

Female Hymenochirus

Although much has been written about spawning triggers such as temperature changes and water levels, well-fed captive-bred Hymenochirus will usually spawn spontaneously once mature. When spawning begins, it is often repeated at an interval of several days for a few weeks, after which the frogs take a break for a several months. In my experience, feeding the frogs during mating often causes them to break off and concentrate on feeding.

Amplexus Typically, male Hymenochirus will begin calling a few days or weeks before mating occurs. Calling occurs underwater, typically while the male is sitting on the bottom. The Hymenochirus mating call sounds like a soft buzzing noise, so you'll need to listen carefully in a quiet room to be able to hear it. Calling is most intense in the evenings, but it's easy to miss it.

Mating (amplexus) occurs most frequently in the mornings and can continue for up to 12-24 hours. The paired frogs perform a somersault close to the surface of the water at which point eggs are released. QuickTime movie of Hymenochirus spawning (185KB).

Eggs When first laid, Hymenochirus eggs are dark spots, 1-2mm in diameter which float at the surface. Over a period of 24 hours, they swell to 5-7mm diameter. The eggs are usually ignored by the parents, but the larvae will be consumed when they hatch, so if you plan to rear any, this needs to be considered. The eggs are sticky and very delicate when first laid, so it is difficult to remove them to a separate container for hatching without damaging them. The easiest solution is to move the adults once spawning finishes. Incubated at 23-27°C (75-80°F), the eggs usually hatch in 5-7 days.

24 hour-old larva
(actual length ~3mm)

Newly hatched larvae are ~2.5mm long and are non-mobile, feeding off their remaining yolk-sac. They begin moving 24 hours after hatching, but do not begin to swim actively or feed for 3-5 days. Unlike Xenopus tadpoles which are filter feeders, Hymenochirus larvae stalk and capture living prey items. Initially, these must be very small - infusoria. Although it is possible to raise a few larvae on alternatives such as Liquifry, all these do is to stimulate the production of infusoria within the tank, and usually pollute the water. Culturing infusoria separately is a much more reliable means of raising larger numbers of larvae.
After 7-10 days the larvae can be gradually weaned off infusoria onto larger foods such as brine shrimp napuli and microworms.

Newly hatched tadpoles are very delicate and highly susceptible to poor water quality. Water changes are important but can be very stressful to them, so the best solution is to use a gentle filter which produces minimal current and to carry out small (e.g. 5%) daily water changes for the first few weeks. As the larvae mature, water changes can be come larger and less frequent (e.g. weekly), but must never be neglected.

21 day-old larva
(actual length ~17mm)

Hymenochirus tadpoles typically metamorphose into aquatic adults 4-6 months after hatching. Adult frogs become sexually mature 10-12 months after hatching.

Identification:

Whatever you may have been told or read, you don't know exactly what species of African dwarf frog you may have! Several very similar species come from the same area in central Africa, and together with the suspicion that many of the frogs in the pet trade may be hybrids, even the experts find identifying these frogs virtually impossible. Take a close look at the three frogs in this photo:

Hymenochirus sp

Two of the main characteristics for differentiating between Hymenochirus boettgeri and Hymenochirus curtipes are:

The length of the legs. Unfortunately, this cannot be seen in the photo, but I've measured them - and all three of these individuals have the same ratio of leg length to SVL (snout vent length).
The size/prominence of the "warts' on the side of the body. The frog at the top is my mystery frog. The two frogs in amplexus were both purchased at the same time, have mated (as you can see) and produced viable offspring. Do my eyes deceive me, or are the warts on the female large and those on the male small?

These phenotypic characteristics are not reliable species indicators! The taxonomy of these frogs is a mess, the literature particularly so. It is said that tadpole morphology is the best way of differentiating Hymenochirus species. Unfortunately, different authors give different versions of this information, e.g: Rabb (1963) Zeitschrift für Tierpsychologie, Band 20, Heft 2, 215 vs. Sokol (1959) Zoologisher Anzeiger 162:156. What needs to be done is DNA studies, but I am not aware of any such data. I'm grateful to Geoff Smith for the following comments:
As far as I'm aware, most of the Hymenochirus frogs in the UK aquatic trade are commercially bred in tropical fish farms in the Far East so their original source will never be known. In the mid 1980s a tropical fish wholesaler told me he imported about 150,000 of them into the UK each year. In the 1980s I had what I believe were both species. H.curtipes was very much stockier than H.boettgeri and with noticeably shorter hind legs and much darker coloration. There is, and always has been a lot of discussion in taxonomical circles about whether frogs belonging to the boettgeri group are, in fact, different species or sub-species. Also, they most probably interbreed, which makes identification even harder. The species offered in the pet trade is almost always H.boettgeri even though they may be labelled as H.curtipes. There are no differences in care or compatibility that I'm aware of. In my opinion your mystery frog is one of the boettgeri group albeit the skin texture, markings and coloration are different from the others. Martin Truckenbrodt of www.pipidae.net is into the taxonomy of and literature about Hymenochirus. The German part of his site has details and illustrations of the different "species" taken from literature.

The good news is that all Hymenochirus species require the same care, so in one sense none of this matters. It does matter from a conservation point of view. Without locality information, it is impossible to maintain named stocks of these frogs, and since there is no information about their wild status in the politically disturbed region from which they originate, it may already be too late to save some species.

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Frank Schafer
Don't be put off by the title and appearance of this book. This is by far the best published information I have seen on the taxonomy and husbandry of Hymenochirus and related genera (Silurana, Xenopus, Pipa). Everything you must know about clawed frogs: aquarium setup, feeding, water, diseases, behaviour, heredity, ecology, distribution in the wild & cultivated forms. Lots of breeding information, coloured photographs, and a detailed taxonomic key. Make sure you get a copy!

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