Jewel fish retain juvenile schooling pattern after crowded development.

Juvenile jewel fish were crowded between 100 and 160 days of age (15 fish/3.6 liters) in a double-walled aquarium sharing water flow with uncrowded siblings (15 fish/69.4 liters). Photographs of schooling in a 73-liter aquarium were made after 30 and 60 days of crowding. Distances maintained between each fish and its 1st-5th nearest neighbors and orientation angles between 1st nearest neighbors were measured. After 30 days, crowded juveniles maintained significant nonrandomly aggregated distances to their 1st-5th neighbors, spacing significantly closer than uncrowded siblings. After 60 days, crowded juveniles maintained both closer, nonrandom distances to 1st-5th neighbors and significantly more parallel orientation to 1st nearest neighbors. Thus, whereas uncrowded juveniles followed the normal developmental pattern of dispersion, crowded siblings retained juvenile spacing behavior.