Hatchling Xenopus Tadpole

Xenopus laevis is the latin name for the African Clawed toad


Hatching

After two days in the egg Xenopus are about 5mm long and have usually hatched. Like the British frog tadpoles (Rana temporaria) they then hang about for a day or so doing very little. They stick themselves to plants or other objects, like the side of a tank, with mucus secreted by a black cement gland on the head where the mouth will form (red arrow).

The mucus is not very strong, so periodically (on average once every 30 minutes) they come unstuck and fall through the water. In shallow water they may come to rest on the bottom.

Swimming

If not attached by mucus, tadpoles often start to swim spontaneously but they will also swim if touched or stroked gently anywhere on the body with something which will indent the skin like a fine hair. During swimming the trunk muscles on each side of the body contract in alternation and contractions start at the head end. As a result, waves of bending pass from head to tail, alternating at from 10 to 25 Hz and driving the tadpole forwards through the water.

Stronger and damaging stimuli to the skin, a brisk water current directed at the head and dimming the light will also start swimming which can last for many seconds. (more 4)

Hatchling tadpoles swim the right way up because their belly tissue is more dense and acts like ballast in a submarine. (more 4.1) In deeper water, the tadpoles often turn head up and swim in a tight spiral (shown in video frames) until they contact the water surface or the side of the dish when they stop and stick on again with mucus. Similar spiral swimming is seen in some baby freshwater fishes. (more 5)

Stopping

Tadpoles can start swimming spontaneously or when they are stimulated but it is just as important that they can stop. This normally happens when their head and cement gland bumps into the surface of the water or some other solid object like a plant or the side of a dish (see video clip above). This kind of stimulus and the tension in the mucus strand when the tadpole is hanging attached have an inhibitory effect on the tadpole. While hanging, it never moves spontaneously and is much less responsive to stimulation. This ability to keep still may make it more difficult for predators to detect and eat tadpoles. (more 6)

Struggling

Like many adult fish, when a tadpole is grasped and held anywhere on its body it makes strong, slow side to side bends of the body to try to wriggle free. We call this behaviour struggling.

Compared to swimming the frequency of the bending movements is slower (5 to 10 Hz), and the waves of bending move in the opposite direction, from the tail to the head. Struggling only occurs while strong stimulation is being applied, for example when the tadpole is in the jaws of a dragonfly larva. (more 7)