Happy together: Schooling confers hydrodynamic and behavioural advantages in a labriform swimmer ( Cymatogaster aggregata ).

Abstract

Fish can enjoy a number of behavioural and hydrodynamic advantages during schooling. Shiner perches, labriform swimmers using primarily pectoral fins and assisting with the caudal fin, were used to study the differences of fin beat frequencies and oxygen consumption between a schooling pair of fish, a solitary fish, and a false pair where a single fish swam alongside a video of a conspecific. By having a fish swimming alongside a video of a swimming fish, compared with the pair of swimming fish, the hydrodynamic effect could be separated from the behavioral/visual effect. It was found that pectoral fin beat frequencies were significantly higher for schools of two-real-fish swimming at 5.5 Bl/s relative to other groups. Additionally the relationship between oxygen consumption and swimming speed was significantly different between treatments, with the false pair treatment having lower oxygen consumption from 3.5 Bl/s and onwards. Our results suggest that the advantages of schooling are not only hydrodynamic but also behavioural, and that the relative importance of behavioural effects depends on the level of swimming activity.