Caging, but not air deprivation, slows tadpole growth and development in the amphibian Xenopus laevis.

Xenopus laevis tadpoles raised in submerged cages in normoxic water develop more slowly than tadpoles raised with access to air. This study distinguishes between the effects of being caged and being deprived access to air on development and growth. Tadpoles were raised in high and low density control tanks and in cages in the same tank that were either completely submerged or with the top exposed to air. Experiments were repeated with the cages in different positions relative to the air stones and with and without the water flow from air stones supplemented with a pump. Whereas caging tadpoles has a large effect on their development and growth, additionally depriving them of air has a small effect and this effect can be removed by optimizing water flow through the cage. The effect of caging, though significant in this study, is small compared to the variation in growth and developmental rates that is commonly encountered within and among controls in lab studies. Caging effects can also be diminished by optimizing rearing conditions and/or having exceptionally vigorous tadpoles. The effects of air deprivation and caging thus pose less of a problem for experimenting on air-deprived (AD) and air-restored Xenopus tadpoles than their inherent variability in growth and developmental rates and their susceptibility to growth and developmental arrest. Further, the effect of air deprivation in this air-breathing amphibian does not pose a conflict with evolutionary hypotheses for lung loss involving lengthening of the larval period and delay in the onset of air breathing.