Soc for experimental Biol Annual Meeting - Salzburg 2012

Stefano Marras (Istituto di Scienza e Tecnologie dell'lnformazione
'A. Faedo', CNR, Italy), Shaun S Killen (University of Glasgow,
Scotland, UK), David J. McKenzie (CNRS, France), John F. Steffensen
(University of Copenhagen, Denmark) and Paolo Domenici (CNR, Italy)
Schooling behaviour is a widespread phenomenon shared by a large
number of fish species. One of the most common benefits of swimming
in a school is the hydrodynamic and energetic advantage obtained by its
members. Fish occupying non-frontal positions can benefit from the flow
generated by the caudal movement of fish swimming in the front.
While previous work has demonstrated that trailing fish show a lower
tail beat frequency (TBF) than leading fish , the extent to which schooling
provides hydrodynamic advantages compared to swimming alone has not
been quantified. We quantified this by filming individual grey mullet Liza
aurata when swimming alone (n=20) and the same fish when swimming
in a school (n=20; eight fish per school, with one focal fish in each school)
at three swimming speeds in a swim-tunnel. TBF was measured in focal
fish swimming to the side of a neighbour, using a range of distances along
the direction of locomotion, spanning one body length (BL) in the front
(+1 BL) and behind (-1 BL) a neighbouring fish.
We found a significant reduction in the mean TBF of fish when
swimming in a school versus solitary fish . Furthermore, the TBF of the
focal fish decreased linearly between the two extreme positions (from
+1 BL to -1 BL), with the lowest values at -1 BL.
This work provides direct evidence that schooling provides
hydrodynamic advantages compared to solitary swimming and that
small changes in the position of an individual fish relative to neighbours
modulates these advantages.
Email addressforcorrespondence: stefano.marras@iamc.cnr.it