Synchronization and collective swimming patterns in fish (Hemigrammus bleheri)

Abstract

In this work, we address the case of red nose tetra fish Hemigrammus bleheri swimming in groups in a uniform flow, giving special attention to the basic interactions and cooperative swimming of a single pair of fish. We first bring evidence of synchronization of the two fish, where the swimming modes are dominated by 'out-phase' and 'in-phase' configurations. We show that the transition to this synchronization state is correlated with the swimming speed (i.e. the flow rate), and thus with the magnitude of the hydrodynamic pressure generated by the fish body during each swimming cycle. From a careful spatio-temporal analysis corresponding to those synchronized modes, we characterize the distances between the two individuals in a pair in the basic schooling pattern. We test the conclusions of the analysis of fish pairs with a second set of experiments using groups of three fish. By identifying the typical spatial configurations, we explain how the nearest neighbour interactions constitute the building blocks of collective fish swimming.

Simple phalanx pattern leads to energy saving in cohesive fish schooling

“…1, Left. This characteristic pattern has already been identified in a previous study on H. bleheri fish triplets (16). As can be observed, this reduced set of geometric parameters determines the most basic school, consisting of a fish triplet, and we use it here to describe the spatial pattern for larger groups of individuals.…”

“…The phase difference is calculated by a peak identification routine on each time series of the tail-beating amplitude. The synchronization effect for H. bleheri was already pointed out in a study with fish pairs (16), in which observations of a large set of experiments showed that >90% of the fish pairs studied were synchronized when swimming at high speed. Fig.…”

“…In addition, the body deformation, characterized by the time-resolved kinematics of the body midline, is recovered from top-view visualizations (as in ref. 16), giving information for each individual on the tail-beating frequency and amplitude. The swimming velocity of the school is set by imposing a flow in a shallow-water tunnel, ranging from 2.5 to 15 cm s −1 .…”

“…This species is particularly cohesive (15), thus representing a characteristic system to analyze collaborating interactions. It has been used in a recent study focusing on the interactions of neighboring fish swimming in pairs and triads-which can be considered the elementary subsystems of a fish school-that reported remarkable collaborative swimming features motivated by energy saving (16). This study especially showed that tail-beat synchronization increases dramatically when fish are forced to swim fast (i.e., in more energy-demanding gaits).…”

On the energetics and stability of a minimal fish school

“…Herskin and Steffensen [11] 24 measured both tail beat frequency and oxygen consumption in sea bass Dicentrarchus 25 labrax, and also found strong evidence for energy saving. Johansen et al [12] estimated 26 that trailing fish in a school (striped surfperch Embiotoca lateralis) benefited from over 27 25% reduction in oxygen consumption, based on correlations between swimming speeds, 28 pectoral fin beat frequency, and oxygen consumption of solitary fish. Marras et al [13] 29 also inferred reduced costs of swimming from measurements of tail-beat frequency of 30 grey mullet Liza aurata alone and in schools, combined with relationships between 31 tail-beat frequency and activity metabolism.…”