Hydrodynamic Advantages Research Articles

Risk of predation, hydrodynamic efficiency and their influence on school structure

Laboratory studies were conducted on 15 schools of blackchin shiners, Notropis heterodon, to determine if they altered their structure in response to changing environmental demands. The hypothesis tested was that fish schools should sacrifice a flat, hydrodynamically efficient structure in favour of an unobstructed visual field in the presence of a predator by staggering in the vertical plane. Ten schools were exposed for two weeks to a simple environment with only a current. For the next two-week period a predator was added. Five control schools were exposed to the simple environment for both two-week periods. Six of the ten treated schools increased their staggering in the vertical dimension as predicted while none of the control schools changed. This result was suggestive that hydrodynamic advantages were sacrificed. Respirometer experiments indicated these fish were capable of achieving some hydrodynamic benefits from schooling but these benefits may be a function of fish size.

Schooling mackerel and herring choose neighbours of similar size

Fish schooling in a submerged sea-cage swam next to neighbours of similar size. Between 57 and 74 fish were used. Extensive three-dimensional data showed the neighbour size effect for two different species, herring and mackerel, during both day and night. These experiments, covering sizes which coexist in the wild, are the first demonstration of the neighbour size choice in fish schools predicted by theories of hydrodynamic advantage.

Swimming Energetics of Striped Bass (Morone Saxatilis) and Bluefish (Pomatomus Saltatrix): Hydrodynamic Correlates of Locomotion and Gill Ventilation

ABSTRACT Swimming patterns of striped bass and bluefish were monitored using a miniature accelerometer to record instantaneous acceleration and instantaneous deceleration during tail-thrusts over a wide range of swimming speeds. In addition, ventilatory excurrent flow patterns were visualized in swimming striped bass by injecting milk via a buccal catheter. Both species accomplish steady swimming with both symmetric and asymmetric thrusts; other transient swimming patterns were observed as well. Over the transition range from active branchial to ram gill ventilation, no measurable change in forward acceleration amplitude occurred with adoption of ram gill flow in both species; this can only occur if drag does not change over the ventilatory transition. From metabolic measurements and from implications about swimming drag deduced from acceleration amplitude, the cost of active ventilation just prior to adoption of ram gill ventilation was estimated to be 8-i % and 8-4% of total metabolism for striped bass and bluefish respectively. Ventilatory effluent flow patterns during cyclic ventilation in swimming striped bass induce substantial turbulence and probably boundary layer separation. Flow patterns during ram ventilation result in streamlined flow over most of the length of the fish. The results show that transfer from active to branchial to ram gill ventilation provides important hydrodynamic advantages to these fishes at cruising velocities.

Evidence against a hydrodynamic function for fish schools

THERE are numerous explanations for the formation of fish schools(1,2), one of the most popular being that the members gain hydrodynamic advantage over solitary individuals(3-6). The model proposed by Weihs(5,6) for the first time makes precise predictions about school structure which can be verified. We report here the first empirical test of this model, and demonstrate that three species of schooling fish do not swim in appropriate positions to gain hydrodynamic advantage.

Reduced Metabolic Rates in Fishes as a Result of Induced Schooling

Abstract Respiratory metabolism data on 15 species of fish representing six families indicate that individuals in a school experienced a reduction in metabolic rate when compared to the same individuals tested in isolation. The reduction in O2 consumption appears to be the result of an interaction of a “calming effect” and a possible hydrodynamic advantage. Schooling and nonschooling species both exhibit this decreased metabolic rate in the grouped individuals. Between isolated and grouped individuals under laboratory conditions, there is no statistical difference in the regression slopes of respiratory metabolism on size.