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Schooling fish under attack are not all equal: some lead, others follow
Stefano Marras1, Paolo Domenici
1IAMC-CNR, Località Sa Mardini, Torregrande, Oristano, Italy. stefano.marras@iamc.cnr.it
Plos One
|June 19, 2013
Summary
Schooling fish (Golden grey mullet) evade threats in a non-random, repeatable order, not a leaderless fashion. Individual position influences reaction time, suggesting a hierarchy in collective anti-predator behavior.
Area of Science:
- Animal Behavior
- Collective Motion
- Ichthyology
Background:
- Fish schools are often perceived as egalitarian, leaderless groups.
- Previous observations noted imperfect synchrony and spatial preferences in anti-predator maneuvers.
- The reaction order of individuals to threats in schooling fish remained unknown.
Purpose of the Study:
- To investigate whether schooling fish react to threats randomly or in a structured, hierarchical order.
- To determine if individual reaction times are consistent over repeated stimulations.
- To explore the relationship between an individual's position and its reaction order.
Main Methods:
- High-speed video analysis of Golden grey mullet (Liza aurata) schooling behavior.
- Observation of spatial-temporal organization during predator-induced evasive maneuvers.
- Analysis of individual reaction order and positional preferences over sequential stimulations.
Main Results:
- Schooling fish evade threats in a non-random, repeatable order.
- Individuals consistently react early or late across multiple threat events.
- Startle order is significantly correlated with an individual's spatial position within the school.
Conclusions:
- Schooling fish exhibit intrinsic heterogeneity, challenging the egalitarian model.
- Positional preferences influence reaction timing, suggesting a hierarchical influence on collective escape.
- Early responders likely play a crucial role in dictating the school's overall escape strategy.
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