Captive Husbandry & Breeding of the Asian Painted Bullfrog (Kaloula pulchra)

Originally published in the Reptiles USA 2013 Annual

The Asian Painted Bullfrog (Kaloula pulcha) is a somewhat cute & comical Narrow-mouthed Toad from Asia that has established itself as something of a regular in the international pet trade. It goes by many pseudonyms but is perhaps best known by its slightly more accurate trade name of Chubby Frog.

Widespread throughout Southern Asia it is a highly adaptable species that makes the most of encroaching human habitat and is believed to be increasing in population despite it’s collection for both the food & pet markets. It has over time been introduced to numerous island countries where it has established populations in an almost pest like manner, a trait that endears itself well to our hobby allowing WC specimens to settle into captivity quickly even when husbandry conditions aren’t 100% perfect.

Growing to around 2-3“ (55-75mm) the Chubby Frog is as its name suggests a rather rotund frog, stocky & robust in stature with a short rounded snout and short limbs suited better to crawling into crevices than jumping long distances. However with a mottled brown background marked by wide black-bordered bands of creamy yellow to pale orange it is far from the images that it’s other names of Painted Bullfrog & Beautiful Kaloula conjure in the mind. Although this may be about to change with recent imports containing Albino individuals and possible Hypo mutations. The underside is a dirty creamy shade of grey and the metatarsal tubercle is developed into a hard spade like projection that enables them to burrow backwards into the earth with surprising speed.

Captive Husbandry

Chubby Frogs make undemanding and hardy captives requiring relatively little space; a standard 15 gallon enclosure (24x12x12”) will adequately house 2-3 adults long-term but with a view to breeding I would suggest groups of 5 – 6 housed in enclosures of 30 gallons (48x12x12”) minimum. There are many choices for a suitable substrate but my preference is for a coco-based blend of re-hydrated coco-fibre mixed with a small amount of composted bark & leaf litter. This provides a free draining substrate and moisture content is easily controlled; something that will prove very important during the breeding cycle. As burrowing frogs the substrate should be relatively deep and for regular maintenance kept damp but not sodden.

Pieces of cork bark, flat rocks & broken terracotta pots can be arranged on the surface to form hides and crevices for the frogs to squeeze in to or burrow under and house plants such as Pothos & Ferns can be added for further aesthetics if you wish.

A water bowl should be present at all times, large shallow heavy ceramic bowls such as dog bowls are best so as not to be disturbed by burrowing activity. The water should as with all amphibians be dechlorinated either through allowing it to stand for 24 hours or treated with an aquarium water conditioner, it is best to refresh the water on a daily basis to avoid the build up of potentially harmful waste products.

Temperature in the enclosure can be maintained using a thermostatically controlled heat mat set between 75-80°F (24-26°C) daytime with a drop in night-time temperatures to 68-70°F (20-22°C). Due to the depth of substrate to be provided heat mats are ideally placed on the side or back of the enclosure and insulated with polystyrene tiles to reflect heat back into the terrarium. Do not be tempted to use foil or foil lined polystyrene to insulate your heat mats as this can cause hot spots resulting in burnt out heaters or cracks in your glass tank.

Humidity should be maintained around the region of 70%, this will be largely achieved through release of moisture from the damp substrate but can be helped and replenished through regular misting. If using a screen topped enclosure you may find it beneficial to restrict some of the ventilation by placing glass or clear acrylic over part of the mesh to help retain humidity.

Lighting is not essential unless live plants are used in the enclosure but it will help define a day / night cycle that could come in handy for breeding as well as adding to your viewing pleasure. I personally have not found any advantage in providing UVB exposure to these frogs and find a good dietary supplement to be adequate in maintaining levels of D3 & calcium take up. If you choose to light the enclosure I would advise using a standard fresh water aquarium tube or one of the many daylight compact lamps available set to illuminate the enclosure for around 12 hours a day.

In the wild Chubby Frogs are reported to feed largely on ants & termites but they take readily to any suitably sized commercially produced feeder insects. Adults can easily take medium to large crickets but they show a preference for a larger number of smaller sized insects such as small-medium crickets, mini mealworms, mealworm beetles and waxmoth larvae. Food items should be fed with a variety of fresh fruit & vegetables before being used and it’s advisable to dust them around once a week with a good calcium & vitamin supplement.

Natural History

One of the most interesting things about Chubby Frogs is their breeding & rapid development but sadly this is rarely observed in captivity. Being a cheap readily available species setting yourself up as a Chubby Frog breeder isn’t going to set you back much initial outlay but likewise it isn’t going to make you any money. However it is an enjoyable experience that will teach you a cycle & techniques that can be adapted to breed numerous Microhylid species in the future.

In the wild Chubby Frogs breed explosively after heavy rains in India this can be between April & May while in other parts of the range it can be year-round. They traditionally utilise temporary rain pools & flooded ditches for breeding that has led to them evolving a very speedy development that can take as little as 2 weeks. This fast rate of growth ensures that the majority of their offspring are out of the water before the pools dry up. With the encroachment of civilisation they have adapted to using garden features & animal water troughs that provide a more permanent source of water and result in a higher survival rate.

In order to reproduce these frogs in captivity we have to mimic the climatic conditions they would experience in the wild. Depending on the origin of the specimens you are working with the cycle can vary slightly in temperature; animals from Vietnam appear to require more cooling than animals of Indonesian or Malaysian origin. As they have been the most prevalent sources of these animals in the trade over the last couple of years I will cover these temperature differences later in this article for you. Scientific literature tells us that specimens from Singapore face very little change in temperature during a typical year and so these may prove to be the easiest to breed in captivity if it is possible to acquire them.

While on the subject of localities there are at the time of writing this article 3 recognised subspecies of Kaloula pulchra. These are the nominate Kaloula pulchra pulchra, the Hainan Digging Frog (Kaloula pulchra hainana) from the Hainan Island in the South China Sea, and Kaloula pulchra macrocephala from Tonkin in northern Vietnam. There is still discussion over the true taxonomic stature of these subspecies, whether they should be treated as species in their own right and if any other subspecies occur over the natural range.

Captive Breeding

In order to give yourself the best chance of success I would advise starting with a brood-stock of 6 to 12 animals at a 2:1 or 3:2 ratio of males to females. The competition between males will stimulate their breeding activity and their calling will help to stimulate the females. Sexing of adults is straight forward, the throat of males is dark dusky grey to black even when out of breeding condition in comparison to the females whose throats retain the pale coloration of the rest of the ventral surface. Once you have your group well settled into captivity and of a good size & weight the cycling can begin. It is usually easiest to time your cycle to coincide with the late autumn or early spring when temperatures are low enough to carry out the cycle without artificial means of cooling.

The initial stage of the cycle is the creation of a cooling period to induce the Chubby Frogs to go into a state of brumation. They do not hibernate to the same extent as temperate species nor do they aestivate like frogs from savannah regions, instead they burrow in to the soil to avoid desiccation and cool temperate but are ever ready to emerge to feed on a warm wet evening. To help stimulate this brumation behaviour humidity should first be allowed to drop in to the 50-60% range and the surface of the substrate allowed to dry slightly this will encourage the frogs to burrow down as you begin to lower the temperature. The amount of food being offered can also be lowered at this time but they do not need to be starved before or during brumation.

Next over a period of 2-3 weeks temperatures should be gradually lowered, for specimens imported from Indonesia & Malaysia I have found a low of 60°F (16°C) to be sufficient. For specimens originating from Vietnam I have had greater success when lowering the temperature further to around 54°F (12°C).

As temperatures get to around the 68°F (20°C) mark you can remove terrarium décor and introduce more substrate allowing the surface of the substrate to dry further untill the first inch or so is almost dry. This will force the frogs to burrow deeper to preserve moisture and will help insulate them from the cold temperatures they are soon to be exposed to.

If lighting the enclosure timings can be gradually lowered from 12 hours to 8-10 hours a day. Light cycles do not appear to be important when breeding these frogs and I have had success in breeding this species with no artificial lighting provided but everything you do to enhance breeding triggers can ultimately increase your chances of a successful mating.

These new levels can be maintained for a period of 4-6 weeks. If activity is witnessed in the evenings a small amount of food may still be offered but throughout this time disturbance should be kept to a minimum. Frogs can be carefully uncovered occasionally to ensure they are still of good health monitoring for signs of desiccation, discoloration of the skin or sudden weight loss. If any signs of ill health are noticed remove the affected individual to a quarantine tank and gradually bring it back to normal maintenance levels.

At the end of your 4-6 weeks you can begin to gradually raise temperature & humidity back to normal levels. The frogs may not begin to become active until humidity levels are raised further to around 85-90% and the normal levels of moisture in the substrate are reinstated. Once your frogs are awake and active its time to introduce them to the first of the 2 rain chamber designs you will use in your breeding attempt. The basis for the rain chamber should be a large deep aquarium, you can use the same aquarium for both breeding set-ups and for rearing the tadpoles so it’s worth splashing out on as large an enclosure as you can afford but ideally I would recommend a minimum of 36x18x18” (90x45x45cm).

Your first rain chamber system will use a circulatory rain system flushing water through the substrate simulating the effect of the heavy monsoon rains. There are several ways you can emulate this, one way and my preferred option is to install a drain and external sump where the water will be filtered and pumped back to the rain bar. This system has some advantages particularly in maintaining water quality however it is a little over the top for the hobbyist breeder. The easier option is to install a false bottom and reservoir in the base of the aquarium using a plastic “egg crate” grid supported on columns with a filter & pump system mounted below.

The first step in creating this rain chamber is to install a small aquarium filter and the pump & tubing for your rain system. Over the top of these pumps you then need to install the plastic grid, this should be a tight fit in the aquarium and well supported to take the weight of the substrate & frogs. Next you will need to lay a barrier that will allow water to drain freely but prevent substrate washing away with it, sheets of fine filter foam, weed suppressant membrane or other close weave cloth work well for this. Cut them slightly larger than required and lap them up against the glass to form a seal that will prevent substrate making it’s way down around the edges. Once this is done you can introduce your substrate; this should be the same free-draining mix we discussed earlier and deep enough for the frogs to burrow fully. Simple décor may be included to provide shelter from the rain.

The rain system should be run initially for several hours early evening and early morning, increased after a couple of days to run all night and occasionally running for a 24 hour stint. Once in this set up you should note an increase in the frogs’ activity, males will begin calling in chorus and females will begin to fatten with eggs. At this time feeding should be increased, offer as much as they will take to ensure they are fattened up ready for their imminent breeding attempt.

After 2-3 weeks in this first rain chamber your frogs should be near ready to breed. Now it’s time to strip out and rearrange the rain chamber ready for spawning.

This time the set up is much simpler, the same rain system can be cleaned and reinstated. A substrate of fine gravel can be laid in the base and sloped up around the sides to provide a gradient and some land area with a water level of 2-3” at the deepest section. Pieces of rock & broken terracotta pot can be placed to provide further platforms for the frogs to haul themselves out of the water. Plants of either the live or plastic variety should be added to the water providing dense vegetation with some open areas. Leaves, twigs and other such floating debris give the impression of a temporary puddle while releasing beneficial tannins into the water that contain anti-fungal & anti-bacterial properties. Water temperature should be maintained at around the 75-77°F (24-25°C) mark, and the rain system run for several hours in the early evening only. Feeding at this time can be reduced again, the frogs minds should be on other things than their stomachs at this point and reducing the feedings will also help prevent drowned crickets.

After a day or two in this rain chamber the males should be calling loudly in chorus, they will call both from land areas and while floating on the surface of the water. Loop tapes of males calling can be made easily thanks to websites such as YouTube and are of benefit to encourage calling in stubborn males or when working with breeding groups lacking in males.

If a female comes into close proximity of a waiting male amplexus will be attempted, literature states that males have difficulty amplexing and so secrete a glue like substance that holds them in place while breeding until the female sloughs its skin and releases him. Having made numerous breeding attempts with Chubby Frogs over a number of years amplexus appears to be rather easily achieved and I have yet to witness a male gluing itself to the female.

If breeding behaviour is still not observed after several days in the rain chamber then flushing with cooler water and turning off the rain for a day or two could be worth a try. Mating usually occurs in the early hours of the morning during the off-cycle of the rain and once spawning has taken place the adults should be removed from the rain chamber and returned to their living quarters.

The small eggs with their black & white poles float at the surface of the water forming a film of spawn. Fertile eggs will always sit black side up and will turn to right themselves if disturbed, at a temperature of 75°F (24°C) fertile eggs will develop rapidly and hatch within 24 hours. The newly hatched tadpoles will fall to the base of the aquarium and lay lifeless for a period while they absorb their yolk sac before becoming free swimming and starting to feed. Once all eggs have hatched the rain system can be removed from the aquarium, the water level raised and an air-powered filter added.

Chubby Frog tadpoles have flat ovoid bodies with eyes positioned towards the sides and can be maintained on a diet of finely crushed fish flake and spirulina algae powder offered in small amounts several times a day. The tadpoles will pull food down from the surface and graze on sunken food, be careful not to overfeed as uneaten food will quickly foul the water.

As mentioned earlier in this article tadpoles of this species have evolved a very fast rate of growth and with a good feeding regime the first froglets can be expected in as little as 2 weeks with subsequent froglets emerging over a further 2 week period.

Morphing at around 3/8’s of an inch (a little under the 1cm mark) froglets can be housed in small groups on a basic substrate such as damp paper towels or fine filter foam misted lightly once or twice a day and cleaned every day or two. Suitable foods at this stage include hatchling crickets, fruit flies, and springtails with a daily helping of calcium & vitamin supplements. If kept clean and well fed the froglets are largely undemanding. They will continue to grow quickly and have the potential to live for 10 years or more.

I hope that this article will inspire some of you to have a go at breeding Chubby Frogs and maybe some of our other more readily available Microhylids.