Breeding and Egg Development of Hymenochirus boettgeri
by David Cecere
I will detail my tank environment and chemistry for those who wish to compare and/or duplicate my conditions. The mating, egg laying and development observations that follow were the first I had witnessed and may not be typical behavior of all H. boettgeri. Two batches of eggs were laid. The first on January 19, 1998 and the second on January 29, 1998.
I am using a 10-gallon (38 liter) rectangular aquarium containing approximately 9 gallons of water. The tank is furnished with a combination of igneous rock, aquarium gravel, plastic plants and African "iron wood". The wood is extremely dense and heavier than water. It is available at most aquarium supply shops.
The tank was relatively immature when the frogs were placed in it, i.e. a full nitrogen conversion cycle had not been established. I decided on the artificial plants because I wasn't certain the water conditions would be right for supporting live plants.
Aeration is provided at one end of the tank by means of an "air stone" partially buried under rocks and gravel.
Filtration is provided by a submersible filter (manufactured by Aquarium Systems) near the source of aeration. The filter contains a mixture of activated charcoal and ammonia locking resin. The flow of the filter is set to maximum. The outflow of the filter is directed to minimize turbulence.
A 50 Watt submersible heater is located at the opposite end of the tank . The daytime temperature is typically 77° F. (25° C.). with nighttime temperatures dropping to 75° F.
The water is typically clear with no offensive odors.
The lighting is a single fluorescent tube with a duration of 12 hours daily. The light is controlled by an appliance timer.
Water Hardness: Soft
I am using a variety of products to condition the water. A phosphate-based powder called Neutral Regulator is used as needed to correct pH and buffer the water toward neutral (7.0). Nova Aqua StressCoat with Aloe Vera is used to remove chlorine, chloramine and heavy metals from replacement water. StressZyme is used weekly to aid in the development of bacterial biology. If ammonia levels go above 4 PPM then AmmoLock2 is used to help convert anhydrous ammonia (NH3-N) to a non-toxic form (NH4).
The development of a fully functional nitrogen-conversion
biology has been slowed by two factors:
I am hoping that the frog tank will continue to develop toward a 0 PPM ammonia, 0 PPM nitrite state. I have achieved this condition in my 10-gallon community tank easily with an under-gravel filter system.
1 to 2 grams of frozen blood worms every 48 hours. The worms are produced in Japan by The Nuromi Company. They are fortified with various vitamins.
I can only estimate the approximate age of the mating pair at about 1 year. The egg laying of Batch 1 occurred on January 19, 1998 starting at around 07:00 PST.
The mating was preceded by several nights of "croaking" that lasted from 1 to 3 hours. The croaking started after the tank light had been out for several minutes. The croaking is apparently done while the frog is submerged. I suspect that the frog is able to push air back and forth between its lungs and vocal chords.
The mating was achieved by the male grasping the female firmly around the abdomen from behind at a point just in front of her hind legs (amplexus). The female did all the swimming with the male keeping his hind legs relaxed. I observed the female swim from the bottom of the tank to the surface where she rotated so that her abdomen was facing upwards and parallel with the surface. I observed a localized extension of her abdomen near her tail. This extension broke the surface of the water whereupon a single egg was deposited. The female returned to the bottom of the tank and repeated the process after a few seconds. A total of 25-30 eggs were laid during my observations.
The egg-laying procedure took only 1-2 seconds and was performed in a near continuous motion. I did not observe any male genitalia nor any sperm.
Amplexus lasted 10 hours, though I wasn't able to observe them continuously during that time. Amplexus did not end until the female became motionless and rigid for some minutes. During that time any mobility was supplied by the male.
After 12 hours the yoke had enlarged by about 50% and had a slightly mottled appearance. The eggs that proved to be non-viable had a yoke that was milky white.
By 96 hours all the tadpoles had emerged from the clear casing and were free swimming. The yoke sack structure was still visible.
At the 24-hour mark I moved approximately 15 eggs into a device normally used to feed live tubiflex worms to fish. This clear-plastic device is cone shaped and extends into the water with small holes to allow the worms to emerge. I had hoped to keep the tadpoles isolated in this device to watch them develop and to ensure that they had a food supply when they were ready to feed. I lost 5 embryos within 72 hours: they stopped developing and turned white. I believe that some of this loss can be blamed on damage that occurred during the move. Additional loss occurred to the embryos developing in the tank. A number of other eggs continued their development where they came to rest within the tank.
The free-swimming tadpoles gradually migrated out of the worm feeder as they were small enough to fit through the holes. My best estimate puts the tadpoles at 3-4 mm. in length and less than 1 mm. wide at 1-2 days of age. I estimate that a total of 15-20 tadpoles hatched.
Three days after the tadpoles left the worm feeder I briefly observed one tadpole swimming in the tank. It was still very small and I soon lost sight of it among the rocks and plants. It is possible that the tadpoles are continuing to develop in hiding. My guess is that they do not need to breathe from the surface after hatching but can respire through their tail membrane. I am hoping that they have been able to feed on the remnants of the adult's food.
January 30, 1998
Batch 2 numbered approximately 100 eggs. They were laid by the same female during amplexus by the same male. Mating appeared to be complete by 07:00 and the bulk of the eggs appeared to be 8-10 hours old. Amplexus ended by 07:30.
I was better prepared this time to transfer and isolate the eggs. I used a modified Monoject 412 syringe to gently remove clumps of eggs from their resting place and put them into a 4" X 3" fine-mesh net that was secured to the side of the tank. I positioned the net so that its rim is about 1/2" above the surface of the water. I transferred approximately 30 eggs that appeared viable. Approximately 20 eggs hatched within 72 hours with the remainder proving non-viable.
I am feeding the tadpoles a product called LiquiFry No. 1 For Egglayers, manufactured by Interpet Ltd.. The product contains infusoria culture and small clumps of white matter made from whole egg. The tadpoles appear to be skimming the milky portion from the surface.
Water Hardness: Soft
The tank chemistry was changing during the time that the eggs were developing. It is my experience that the pH tends to drop as the tank matures. The delta between the levels of January 19 and February 1 suggest that a full nitrogen conversion cycle is becoming operational. I have taken extra care not to change the pH too suddenly to avoid putting the tadpoles into shock.
I made a surprising discovery. I spotted a relatively large tadpole swimming in the tank. I was able to transfer him to the net and examine him with a 10X loop. He appears to be the sole surviving tadpole from Batch 1 and I have named him Lucky. He is approximately twice the size of those from Batch 2. I have observed Lucky eating small bits of the white matter from the LiquiFry.
Under 10X magnification it is obvious that the newly hatched tadpoles swim inverted. They swim slowly in this position less than a millimeter below the surface. They apparently feed in this manner but I've had difficulty observing their mouths clearly. When they are resting they will typically right themselves. They will swim away very quickly from a small disturbance of the water in their vicinity.
After 72 hours many of the tadpoles from Batch 2 are swimming in a righted orientation.
At 72 hours the tadpoles have developed dark pigmentation along their body and tail. Their bodies have taken on a more square shape when viewed from above. Lucky (at 10 days of age) has developed gold flecks that run laterally from between his eyes to the tip of his tail.