Evidence against a hydrodynamic function for fish schools

Partridge, Brian L.; Pitcher, TJ

doi:10.1038/279418a0

Cited by 137 publications

(80 citation statements)

References 7 publications

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“…These issues were already remarked on by Weihs (5) and have been the center of criticisms in previous studies (19,38,39), because achieving the required conditions to maintain such idealized diamond patterns may be too constraining for a school. Choosing a phalanx pattern appears to be the selected strategy to optimize swimming performance, combining social and mechanical priorities together.…”

Section: Discussionmentioning

confidence: 86%

Simple phalanx pattern leads to energy saving in cohesive fish schooling

Ashraf

Bradshaw

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

142

145

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The question of how individuals in a population organize when living in groups arises for systems as different as a swarm of microorganisms or a flock of seagulls. The different patterns for moving collectively involve a wide spectrum of reasons, such as evading predators or optimizing food prospection. Also, the schooling pattern has often been associated with an advantage in terms of energy consumption. In this study, we use a popular aquarium fish, the red nose tetra fish, Hemigrammus bleheri, which is known to swim in highly cohesive groups, to analyze the schooling dynamics. In our experiments, fish swim in a shallow-water tunnel with controlled velocity, and stereoscopic video recordings are used to track the 3D positions of each individual in a school, as well as their tail-beating kinematics. Challenging the widespread idea of fish favoring a diamond pattern to swim more efficiently [Weihs D (1973) Nature 241:290-291], we observe that when fish are forced to swim fast-well above their free-swimming typical velocity, and hence in a situation where efficient swimming would be favored-the most frequent configuration is the "phalanx" or "soldier" formation, with all individuals swimming side by side. We explain this observation by considering the advantages of tail-beating synchronization between neighbors, which we have also characterized. Most importantly, we show that schooling is advantageous as compared with swimming alone from an energy-efficiency perspective.fish swimming | collective dynamics | pattern formation | synchronization | energy efficiency T he dynamics of animal groups is driven by many different factors, such as foraging, social life, or survival instinct against predators (1). The collective movements are built from local interactions between the individuals constituting the group (2, 3). Apart from behavioral aspects, the benefit from schooling has often been associated with group optimization in terms of hydrodynamic resistance (4). A fish school represents a typical case of such cohesive and collaborative complex systems. The fluid dynamical mechanisms influencing the motion of fish in a school have been described in essence in the early study of Weihs (5). He demonstrated, using a 2D model, that if each fish maintains a specific position within the school, forming a diamond pattern, the hydrodynamic interactions will globally improve the swimming performance. The basic idea is that fish in a school optimize swimming by interacting constructively with the vortices shed by the local leading individuals; such constructive interactions require a precise synchronization between fish. This study has been followed by an extensive number of studies modeling or simulating fish school swimming configurations to validate Weihs' hypothesis (6-8). It has been shown that by following this strategy, fish could improve their efficiency by ∼20% (8, 9). However, the idea that a beneficial situation in terms of swimming power can be achieved for the group by maintaining a specific complex pattern remai...

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Section: Discussionmentioning

confidence: 86%

Simple phalanx pattern leads to energy saving in cohesive fish schooling

Ashraf

Bradshaw

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

142

145

View full text Add to dashboard Cite

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“…For fish schools, Weihs predicted that a diamondlike configuration of the positions of individuals is energetically optimal [14]. However, there is little biological evidence that such configuration occurs in nature [15]. In a more recent study, several different configurations (line, phalanx, diamond, and rectangular) are all found to be hydrodynamically advantageous [16].…”

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confidence: 99%

Flow-Mediated Interactions between Two Self-Propelled Flapping Filaments in Tandem Configuration

2014

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The mechanism by which aggregates of active swimmers are formed is an intriguing problem. In this Letter we show that, for two tandem self-propelled filaments driven by harmonic plunging motions of identical frequency and amplitude, stable configurations can be spontaneously formed by locking the trajectories onto the vortex centers. Further analysis indicates that the grouping energetics is also dictated by the wake vortex structure. The rationale behind the energetic advantage of the follower is found to be the interplay among actuation, self-propulsion, and the vortical fluid environment.

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“…To achieve optimal hydrodynamic benefits, similar (but not identical) school structures are required (see Weihs 1975 for a more complete description). Pitcher (1986) rejects the vortex hypothesis based on the results of Partridge & Pitcher (1979) in which only four of 659 cases had fish in the positions predicted by Weihs (1975). Further, Pitcher argues that this mechanism would be evolutionarily unstable as only members in alternate rows of the school realize any energy saving.…”

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confidence: 83%

“…If a hydrodynamic function is achieved at the expense of an anti-predator function, then schools providing a hydrodynamic advantage should only be observed in circumstances where an antipredator function would be of little value. Therefore, it would not be expected that Partridge & Pitcher (1979) would observe a hydrodynamic function in schools of prey species in an unfamiliar laboratory environment. In this situation, the benefits of an antipredator function would exceed that of a hydrodynamic function.…”

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confidence: 97%