Jewel fish retain juvenile schooling pattern after crowded development

Abstract

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.