Timing of dispersal in juvenile jewel fish during development is unaffected by available space

The spatial distributions of 2 groups of sibling juvenile jewel fish were examined between 58 and 99 days of age to determine the effects of spatial experience on the timing of dispersal from a more aggregative behavioral mode. One group was provided a seminatural 1000-liter aquarium, the other with 70% less space per fish, but both groups were able to observe the same number of fish. Using a computer and digitizing tablet, distances between 1st-6th nearest neighbors were measured from time-sampled video recordings of spatial distributions in either overhead or underneath plan views. Both groups exhibited changes in aggregative behavior that were remarkably similar. Between 65 and 92 days of age, both groups showed gradual dispersal, which accelerated abruptly at 93-99 days of age. These results suggest that the timing of dispersal is regulated by developmental processes operating independently of spatial experience.