Species-specific schooling behaviour of fish in the freshwater pelagic habitat: An observational study.

Social living of animals is a broadly occurring phenomenon, fish schooling behaviour is an excellent example, although poorly studied in freshwater systems. The composition of fish schools, species-specific schooling tendencies and preferences of adult fish were studied in the pelagic habitat of Rimov Reservoir, Czech Republic. A total of 34 days (16 h per day) of video recordings captured in the clear water period of three seasons was analysed. From four species identified as school-forming species - bream, bleak, roach and perch, 40 % of the individuals observed formed schools of 3-36 individuals. Although conspecific schools prevailed, 20 % of individuals formed heterospecific schools, except bleak that schooled strictly with conspecifics. Schools were composed of individuals of similar body size and life strategy. Heterospecific schools were significantly larger than conspecific schools and showed uneven proportion between species, i.e. one species being more abundant when the school dimension increased. Probability of encounter in bleak was lowest and proved highest inclination for schooling. Gregarianism levels depended on species morphology and body size, with larger and morphologically advanced fish tending less to sociability. This indicates that the anti-predator function of schooling behaviour is intensified with rising vulnerability of the species. This article is protected by copyright. All rights reserved.