Hymenochirus boettgeri may breed repeatedly throughout the year under captive conditions.  Males call and exhibit territorial behavior.  In mating the male makes stimulatory and inhibiting movements in response to the female's actions.  Egg-laying is accomplished in an upside-down position at the surface of the water.  Females unwilling to lay give a variety of rejection signals.  The mating behavior has many parallels to what is known of other primitive frogs, especially Pipa pipa and  Xenopus laevis.

Remarks on the taxonomy and external morphology

     As far as we have been able to determine, the common African "underwater frogs" in the aquarium trade in the U.S.A. are H. boettgeri (TORNIER).  Occasionally H. curtipes (NOBLE) is imported.  Differences in the behavior of the tadpoles of H. curtipes and H. boettgeri have already been reported (SOKOL 1959), and the morphology of the adults suggests that behavioral differences may also be found in them.  The species mentioned appear to be valid, although some of the descriptions in the liturature are confusing and variation has not been adequately studied.

H. curtipes (NOBLE 1924) is a short-legged species with small eyes and relatively smooth large tubercles on sides and thigh.  Its tadpole has a flattened body, very dark dorsum with supraocular and paravertebral patches of golden iridocytes, and a distinctive pattern of dark blotches on the tail (SOKOL 1959).  H. boettgeri (TORNIER 1896) is a long-legged species with prominent variably spinose tubercules on the sides of its thigh.  SOKOL (1962) has described the anatomy of the tadpole of boettgeri in detail.  According to him, it has silvery iridocytes on a generally gray dorsum and a weakly pigmented tail.  In the tadpoles we refer to this species, the iridocytes may be golden as well as silver and the tail has a distinctive longitudinal arrangement of dark coloration where melanophores concentrate about the aorta, caudal vein, and especially the top and bottom of the caudal musculature.  Golden iridocytes are also found on the top of the caudal muscles.  The tail fin is pigmentless.
...

Specimens, methods and terminology

     Most of the observations that follow were made between January 1961 and February 1962 on 6 males and 7 females from a group of 30 specimens of Hymenochirus boettgeri obtained from the import firm of  Paramount Aquarium, Ardsley, New York.  The frogs were shipped from Leopoldville, Republic of Congo and were three quarters grown when received in October, 1960.  Additional observations were made on 11 offspring of a female of unknown provenance and a male obtained in the summer of 1960 from Paramount Aquarium.  For the most part the animals were maintained in 24 X 24 X 44 cm. aquaria filled to a depth of 10 cm. with soft water (pH 7.6-7.8) at temperatures which we varied from 19° C. to 30° C.  A liter or two of water was added to the tank daily after shed skins and feces were removed by siphon.  The aquaria, which had glass or slate bottoms, were provided with small rocks and aquatic plants or plastic weeds.  The frogs were fed every day or two with Tubifex or, infrequently, Enchytraeus.  About ten animals were kept in the tank where breeding occurred, and never more than four of these animals were males.  A crowded tank seemed to discourage breeding activity.
...

Sex dimorphism in anatomy and sounds

     Females of Hymenochirus boettgeri from the Congo reach a larger size than males—up to 35 mm. in snout-vent length, 3 mm. longer than the largest male we have seen.  However, with well nourished specimens even small adult females are easily distinguished by their stout abdominal regions from the trimmer and slimmer males.  The posterolateral part of the head in males is noticeably swollen because of the large size of the orbiculate tympanum, which is not fused to the skin.  The tympanic diameter of the males is approximately double that of the females (up to 2.5 mm. versus 1.2 mm.).

     A conspicuous characteristic of the adult males is the lateral post-axillary subdermal gland, visible externally as a round whitish spot or raised area where it is attached to the skin.  It is actuallty teardrop-shaped, about .5 mm. thick, 1.5 mm. wide, and up to 2.5 mm. long.  In periods of sexual activity the gland enlarges, the skin about it becomes more vascularized, and the center of the gland appears as a reddish spot.  The gland's products are presumably shed to the outside at such times.
...

     We have found that males are able to come into breeding condition throughout the year under captive conditions.  Our males came into calling condition frequently during late winter, early spring and fall.  Periods of calling lasted from 2 to 7 days and were separated by quiet periods of 4 to 6 days.  In the months of June, July, August, December and January calling periods were shorter and the time between was as long as 2 weeks.  Temperature and sunlight seeem to be important factors in stimulating the males.  Adult males were kept at temperatures of 23° C. to 24° C. for months under incandescent and fluorescent lights without any signs of of breeding activity, but when placed in sunlight, with temperature varying from about 21° C. to 22° C. at night to a high of about 28° C. during the day, they rapidly sprang into breeding condition.
...

Eggs, tadpoles and general development

     The greatest diameter of the eggs is about 1.5 mm.  The diameter across the inner jelly layer is approximately .90 mm. and the yolk diameter seldom exceeds .75 mm.  The vitellus has a dark brown animal and a cream-colored vegetable pole.  The outer jelly layer is rather sticky and the eggs as a result are apt to become attached to plants, the frogs, etc., or simply to become coated with debris.  The eggs that are suspended at the water surface appear to be held there by surface tension alone, with only a slight deformation of the outer jelly layer at the top.  In one laying we scooped away 25 eggs  left at the surface within a minute after they were laid.  Only one of these surface eggs developed, in contrast to about 20 per cent survival for the 100 eggs that had sunk to the bottom.  Both sets were kept in the same container.  Such differential fertility of surface and bottom eggs has not prevailed in other layings of which we have accurate records.

     A close study of five layings of two of our home-raised females indicates that imperfect turnover technique is probably the main cause of infertile eggs.  Proportionately more of the eggs that fall to the bottom are ordinarily the result of imperfect turnovers.

     Hatching takes place within 48 hours at temperatures between 22° C. and 25° C.  Higher temperatures cause more rapid development but more abnormalities also seem to occur.  For the first two or three days after hatching the tadpoles are quiet—they fasten themselves to objects, lie on the bottom, or suspend themselves from the surface film by mucus threads.  At 6 or 7 days the tadpoles begin feeding on protozoa, etc.  Many objects are sucked in and expelled immediately.  After 11 or 12 days newly hatched brine shrimp larvae are satisfactory food.  Young tadpoles cruise slowly near the surface in search of prey.  Limb buds appear in the third week, and transformation takes place as early as the sixth week at temperatures ranging from 20° C. to 24° C.
...

End of Excerpt

Glossary

aor·ta (A-'or-t&) : the great arterial trunk that carries blood from the heart to be distributed by branch arteries through the body (see illustration below)
cau·dal ('ko-d&l) 1 : of, relating to, or being a tail
di·mor·phism (dI-'mOr-"fi-z&m) : the condition or property of being dimorphic or dimorphous: as a : the existence of two different forms (as of color or size) of a species especially in the same population <sexual dimorphism>
dor·sum ('dor-s&m) 2 : BACK; especially : the entire dorsal surface of an animal
Enchytraeus : Enchytraeus albus : a live-bearing white worm that grows in decaying vegetable matter.
ir·id·o·cyte (i-'rid-"O-cIt) colored spot
me·la·no·phore (m&-'la-n&-"fOr) : a melanin-containing cell especially of fishes, amphibians, and reptiles : mel·a·nin ('me-l&-n&n) : a dark brown or black animal or plant pigment
mor·phol·o·gy (mor-'fä-l&-jE)1 a : a branch of biology that deals with the form and structure of animals and plants b : the form and structure of an organism or any of its parts
or·bic·u·late tym·pa·num (or-'bi-ky&-l&t 'tim-p&-n&m) : the circular outline of the structure that comprises the frog's ear
par·a·ver·te·bral ('pär-&-"v&r-'tE-br&l) alongside the backbone
post-axillary subdermal gland : a gland located behind the point where the forelimb meets the body and under the skin.
pos·tero·lat·er·al (pos·tero·lat·er·al) : behind and to the side
pro·to·zo·an  (prO-tO-'zO-"än) plural pro·to·zoa (/-'zO-&/) : any of a phylum or subkingdom (Protozoa) of chiefly motile and heterotrophic unicellular protists (as amoebas, trypanosomes, sporozoans, and paramecia) that are represented in almost every kind of habitat and include some pathogenic parasites of humans and domestic animals
spi·nose ('spI-"nOs) : spiny
su·pra·oc·u·lar ('sü-pr&-'ä-ky&-l&r)  above the eye
tax·on·o·my (tak-'sä-n&-mE) 1 : the study of the general principles of scientific classification  2 : especially : orderly classification of plants and animals according to their presumed natural relationships
tu·ber·cle ('tü-b&r-k&l) 1 : a small knobby prominence or excrescence especially on a plant or animal
tu·bi·fex ('tü-b&-"feks) : any of a genus (Tubifex) of slender reddish oligochaete worms that live in tubes in fresh or brackish water and are widely used as food for aquarium fish
vas·cu·larized ('vas-ky&-l&rIzd) : a state of increased blood supply
vi·tel·lus (vi-'te-l&s) : the egg cell proper including the yolk but excluding any albuminous or membranous envelopes


1 aorta, 2 pulmonary artery, 3 left atrium, 4 left ventricle, 5 right ventricle, 6 right atrium