The larvae of Ambystoma opacum generally spend daylight hours hidden on pond bottoms. At night they migrate upwards and remain suspended near the surface in a stratum across the pond. Stratification lasts for several hours; during this time the larvae feed. Vertical migration and stratification do not occur in small larvae or larvae approaching metamorphosis. Similar behavior occurs in larvae of A. tigrinum and members of the A. jeffersonianum complex, but was not observed in larval A. maculatum or Notophthalmus viridescens. Migration and stratification are correlated with decreased light intensity and perhaps movements of food organisms. Where more than one species of Ambystoma occurs in the same pond there is a temporal sequence of stratification. Sequential stratification perhaps decreases competition for food between larvae of sympatric species of Ambystoma.
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Anderson et al. (1967) studied this question.