Maintenance of the Blue Poison Arrow frog

Edwin Blake and Douglas Sherriff, 
Reptile Section Edinburgh Zoo
Photograph: Kevin Du Rose
Last update: 17 August, 2002

INTRODUCTION

Dendrobates azureus

Dendrobates azureus has a very limited distribution occurring in a few isolated "islands" in the Sipaliwini Savannah in Southern Surinam. These "islands" are threatened not by human interference, but by the encroachment of the savannah itself. This frog is probably the rarest of the genus and is certainly the one at greatest risk of extinction in the wild. Dr. Hoogmoed of the Dutch Natural History Museum only discovered it as recently as 1969.

In 1989 we first made contact with various zoological collections and private breeders regarding obtaining this rare and attractive amphibian and, in January 1992, six males and four females from three unrelated lines arrived from Baltimore Aquarium in the USA. Unfortunately they were delayed in transit for 24 hours which almost resulted in tragedy, due to their being left in an unheated cargo area. On arrival, the container was rather hurriedly opened and it appeared that they had all perished. They were all placed in shallow, cold tap water so as not to initiate a shock response and their heads were rested on dishes to prevent them from drowning.

The water temperature was gradually increased over a 30-minute period until tepid and by this stage, to our astonishment, seven of the frogs had very faint heartbeats and were showing signs of very slight throat movement. After 2.5 hours the remaining three had very faint heartbeats visible, but were not breathing. At this point we decided to try artificial resuscitation and one end of a fine catheter tube was inserted into their mouths and, with the other end in the keepers, rhythmic flows of air were gently passed down the tube causing the frogs' throat to palpate. This was continued for five minutes in 15 over a three-hour period and resulted in the frogs regaining voluntary irregular breathing. By this stage everything possible had been done to revive the frogs, and only peace and quiet would benefit them. They were placed in small plastic boxes lined with damp paper tissue and kept in a human incubator at 30°C overnight.

The next morning the stronger seven frogs had fully recovered and were moved to small aquariums and later that day were witnessed feeding. The other three were incapable of movement, but were also transferred to small aquariums which were brightly lit in the hope that this would stimulate them. After eight days the seven had fully recovered, but the (other) three still hadn't the strength to feed and had lost about 60% of body condition. By the 13th day one of the three died (a female) and it was obvious that after such a time period the other two would not survive without further assistance. It was therefore decided to attempt force-feeding using a paste consisting of crushed hatchling crickets, fruit flies, water and a liquid multi-vitamin (Abidec). This was administered once a day by passing a fine catheter tube down into the stomach and very gently pushing a small amount of food down via a syringe. This process was continued for eight days, during which time the frogs regained condition. The following day, 22 days after their arrival, these two frogs at last initiated a feeding response when they started striking at live insects placed in the tank.

The 9 (6.3) frogs remained off exhibit for a further two months by which time we were sufficiently satisfied with their overall condition. Three pairings were selected at this time for exhibit, each pairing housed separately in similarly designed units.

HOUSING
Each unit measures 175 x 90 x 90cm and incorporates a pool, waterfall and stream. Cage decor includes granite stone walls, dense planted areas, branches and pieces of cork bark. Substrates used include peat moss in the planted areas, gravel chips in the stream and bark chippings. Sphagnum moss was used for aesthetic purposes. Lighting is provided by a 120cm "Northlight" fluorescent striplight linked to a time clock and on a 12:12 cycle. Ambient air temperatures of 22°C are provided by heat pipes, which run under the cage fronts. Additional heat is provided by a 15 watt Ceramic heat bulb suspended in the centre of the unit and provides a hot spot of 28°C. This provides the frogs with a range of temperatures to select from. Basic maintenance is employed to minimise disturbance. Pools are cleaned every second day and the units are sprayed daily (in the morning).

DIET
These frogs have massive appetites and need to feed regularly on very small insects. For this reason it is essential that food items are cultured on the premises. At present we culture the following insects.

1. Vestigial winged fruit fly Drosophila melanogaster

2. Giant "winged" non-flying fruit fly Drosophila sp. (Costa Rica)

3. Giant "winged" flying fruit fly Drosophila sp. (UK)

4. European black crickets Gryllus bimaculatus

5. Waxmoth larvae Galleria mellonella

During the summer months we collect greenfly and their aphids from sycamore Acer pseudoplatanus and nettles Urtica vulgarii and blackfly aphids from elder Sambucus nigra and bramble Rubus fruticosa. Collecting flies and aphids from plants with a toxic sap should be avoided at all costs.

Prior to being used as food the Drosophila and crickets should be fed on a vitamin enriched drink. This is straightforward, and the following system is used at the Zoo with great success. The flies are knocked into a spare jar from their cultures via a funnel (to prevent escapes) and a piece of cling film placed over the top of the jar which is placed in the fridge to cool the flies down. Meantime a fruit and vitamin drink is prepared for the flies. We use freshly squeezed orange juice and Abidec multi-vitamin drops or scraped banana flesh and Abidec. The orange drink is soaked into a cotton wool pad and the banana placed in a plastic lid. This is then placed in a plastic tank together with an empty plastic lid. The cooled flies are then emptied into the plastic lid and a piece of tissue paper is placed over the top prior to the ventilated lid being fitted (this will prevent the flies from "sweating"). The flies should be left to feed for about 30 minutes. Reverse the process to collect flies from the tank i.e. fridge first.

A multi-vitamin powder should be sprinkled over the flies prior to use. Hatchling crickets can be fed on the orange drink. The banana is not used, as they will stick in it. The greenfly and aphids should be dusted with a vitamin powder prior to use. If dishes containing the above vitamin drinks or pieces of fruit are placed within the frog units these will help keep the flies localised.

SEXING
The sexing of D. azureus when adult is straightforward, the most obvious differences being size; females grow to 48mm in length whereas males seldom reach 40mm. In build females are much plumper than the males and in the size of the front toe discs the males' are much larger and heart-shaped. This last characteristic is also a guarantee of sexing in sub-adult specimens where the size and build cannot be differentiated between individuals, and is usually evident at 6-8 months of age.

COURTSHIP AND EGG-LAYING
Courtship in this species is mainly conducted by the female. When she is ready to spawn she will approach the male and gently stroke him on the body with her front feet. The male will respond to these approaches with an almost inaudible "buzz" call repeated every 10 seconds or so. It is actually easier to see the male calling than to hear him; his body inflates with air and then simultaneously the body deflates and the throat is expanded. He will then lead the female to a suitable spawning site. The "honeymoon hut" (a half coconut shell placed over a plastic dish containing a section of plastic leaf) is invariably used by this species. If the female is satisfied with the male's choice she will stay inside and spawning takes place; if she is not, she will leave and the process starts all over again. The pair at this time should not be disturbed. The eggs, which number between three and six (one female laid 11) and measure 3.5mm in diameter, should be left in the cage until it is certain that the male has fertilised them. A safe time period between egg laying and removal for incubation is 24 hours. A good indication to whether a spawning has taken place unnoticed is if the male is observed drawing water into his vent in order to wet the eggs. The female can produce up to two clutches per week when in good condition.

EGG INCUBATION
The dish containing the eggs is placed in a container with just enough tepid water to touch the base of the eggs. Then the container is sealed or covered to prevent evaporation and kept at 24°C. During incubation they are checked daily and every third day are lightly sprayed or the container tilted, causing the water to flush over the eggs. Any infertile eggs are usually removed though we have recently stopped this practice as they cause fertile eggs no harm and if not done carefully damage to healthy eggs can occur. We have never encountered problems with fungal infection mentioned by other Dendrobates breeders. After about 14 days the first tadpoles will emerge and remaining eggs may take a further 3-4 days.

TADPOLE CARE AND USE OF UV
This is the most critical part of Dendrobates husbandry as failure to provide the tadpoles with the correct diet and ultra-violet (UV) exposure will result in weak or deformed metamorphosing froglets. We have been working on this aspect of tadpole husbandry since the latter part of 1988 when working with Dendrobates auratus obtained as wild adults in 1986. We started having problems with what has been termed spindly leg syndrome. This takes the form of metamorphosing froglets having very weak front legs; even to the extent that limbs cannot be released from the branchial chambers. This disorder should be termed rickets rather than spindly leg, which means nothing. We began by working on the nutritional and UV requirements.

All tadpoles were fed as in previous years on STAPLE DIET TETRA FLAKE FISH food, but when the first signs of back limb development were noticed the diet was changed to eight parts of powdered TETRAMIN to two parts vitamin powder (SA37) and one part of powdered cuttlebone. Also at this stage they were exposed to an actinic 09 UV fluorescent strip light for 15 minutes once a week. This resulted in all froglets metamorphosing perfectly. One group of tadpoles was then used as a control; these received the modified diet, but were not exposed to UV. All these tadpoles had to be destroyed due to rickets. It became apparent that our adults were producing less viable eggs. Hatch rate had dropped to around 20% and the diameter of the eggs had reduced greatly. Therefore our next line of approach was to expose the parent stock to UV to see if this would result in healthier eggs being laid.

Adults were exposed to 20 minutes UV once a fortnight during feeding times to ensure exposure. Each clutch of eggs laid was monitored and after the fourth clutch the eggs had increased in size and hatching rates had increased to 95%. In 1991 we stopped using the Actinic 09 striplight and started using the WOTAN ultra vitalux, a 300-watt UV reflector bulb. The guidelines for use of this bulb are 15 minutes of exposure from a distance of 45cm for frogs and tadpoles once a month.

Back to the tadpole care aspect, this species of tadpole is cannibalistic and must be housed separately. Standard size coffee jar lids are suitable housing for tadpoles filled 3/4 full of tepid water. Improvements to the diet for the D. azureus tadpoles include the addition of pieces of mussel, snail, earthworm and cat food. The water in the lids must be changed every day to prevent fungal/bacterial infection.

METAMORPHOSIS
After the froglets have absorbed 3/4 of the tail they can be housed together. This is possible only at this stage as the mouth has changed and they are no longer cannibalistic. They are kept in a small aquarium with 1cm of water and pieces of slate, half flower pots and plastic leaves to hide and dry out. When the tail is fully absorbed the water is replaced with damp peat and a shallow water dish is provided. This is 3/4 filled with gravel to prevent accidental drowning. In the second month they are given UV exposure at a distance of about 45cm for about ten minutes; this is increased to 15 minutes a month when half grown. During exposure all cage furniture is removed to ensure all froglets are exposed. It is important to continue UV work during the growing stages to ensure correct bone development.

NOTES OF INTEREST
One pair of D. azureus was allowed to care for their eggs. This provided information on male care and transport of the tadpoles. Three clutches of eggs were cared for at one time. He carried tadpoles for up to two days before depositing them in the numerous small water dishes provided. On one occasion the female transported a tadpole and deposited correctly. The male, whilst carrying two tadpoles, was seen calling and went through all the courtship previously described and fertilised a clutch of eggs before depositing the tadpoles the next day. One of the male frogs that was force-fed successfully fertilised eggs in mid-1993.

CONCLUSIONS
Each pair of frogs was limited to producing 25-30 froglets and after this number was reached further eggs were destroyed. This was carried out to prevent over representation of each line. The reproduction of this species in captivity has been problem free, although egg fertility has been low possibly due to the young age of the pairs. We will be working on this aspect in 1994 if this continues. The condition termed "spindly leg syndrome" is an easily prevented disorder if the methods described in the text are followed. It is the responsibility of all individuals to ensure they are producing healthy viable offspring for the long-term future of this species.

We will be placing D. azureus on a studbook and are currently working with several European collections so that satellite groups can be managed abroad. It is also intended to bring new lines into this collection from within Europe.

It has been reported by private individuals that the habitat in which D. azureus is found had been badly damaged by fire. After investigation by Dr. P. E. Oubter, Department of Zoology, Anton De Kom University, Surinam, on our behalf this has not been the case. This species, however, does require fieldwork to update information regarding its distribution, population, size and habitat and we hope to be involved in this aspect within the next two years.

ACKNOWLEDGEMENTS
We would like to thank Baltimore Aquarium staff for the founder stock and Dr. P. E. Oubter, Department of Zoology, Anton De Kom University. Postbus 92J2 Paramartibo Surinam.

PRODUCTS MENTIONED IN TEXT
Tetramin Flake Food: Tetrawerke, Dr. Rer. Nat. Ulrich Baensch GmBM.D4520 Melle 1 Germany.

SA37 Vitamin Powder: Intervet UK Ltd. Science Park. Milton Road, Cambridge.

Abidec Multivitamin Drops: Warner Lambert Health Care, Lambert Court, Chestnut Avenue, Eastleigh, Hampshire SO5 3ZQ

Wotan U.V.B. 300 w: Osram Ltd., Lea Green Road, St. Helens WA9 4QQ.

Actinic 09 U.V. Philips Lighting, PO Box 299, City House, 420-430 London Road, Croydon CR9 SQR.

Ceramic Heat Bulb: Philips Lighting, PO Box 299, City House, 420-430 London Road, Croydon CR9 SQR.

Northlight G.E. Lighting Ltd. Miles Road Mitcham Road, Surrey RR4 3YX.

 

Dendrobates azureus

Mick Bajcar
Last update: 17 August, 2002

A letter has been received from Dr. Jack Frenkel in the USA. In it he says:

I came across an article News about azureus (Edinburgh Zoo): News from Edwin Blake and Douglas Sherriff of the Edinburgh Zoo, 1995. On p.8 under Final Result he says that they gave every pair the opportunity to produce 25-30 young frogs, and that thereafter they destroyed the eggs to avoid overproduction. Perhaps they would agree to donate their overproduction to the British Dendrobatid Group. In the US, there is at least one import from the Guianas and sooner or later we could exchange this stock for that of Edinburgh. The Edinburgh practice appears wasteful. You do not have to worry about inbreeding for 20 generations!

I have sent a copy to Edwin Blake and Douglas Sherriff asking for their comments but have not yet received a reply. This will, hopefully, be included in the next Newsletter. Jack continues:

I have been frustrated about not hearing any more about the very reasonable hypothesis of iodine prophylaxis for spindle leg disease. Too often there are only anecdotal observations.

Having read the article by Edwin and Douglas, and having seen their magnificent D. azureus and tinctorius at the Zoo, in the next Newsletter I would like to discuss the requirements of UV lighting for our animals. Please send me details of your methods and thoughts.

December 1996

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