Rheoreaction in Danio rerio (Cyprinidae): Influence of Flow Velocity and Availability of Still Water Zones

Abstract

The results of an experimental study of the influence of the flow velocity on the rheoreaction indices of Danio rerio, rheopreferendum and the ratio of the frequencies of various types of rheoreaction, are presented. At a crucial for fish flow velocity of 0.30, their rheopreferendum is positive, while at 0.80, negative. The ratio of rheoreaction types at these velocity levels was typical for resident fish. At a crucial flow velocity of 0.45, the rheopreferendum was not expressed, and the fish behavior was typical for upstream-migrating individuals. A decrease in the accessibility of the limnozone (limitation of the zone’s entrance width) in the circular tank reduces the number of fish returning to it and changes the ratio of their rheoreaction types. At the maximum width of the entrance (19 cm), the ratio of zebrafish rheoreaction types reflects the behavior characteristic of migrating individuals, while for all other variants (10, 3, and 1 cm) it is typical for resident forms. It is shown that the rheopreferendum is a less complete and reliable assessment of rheoreaction than the ratio of rheoreaction types. The applicability of rheoreaction indicators is considered.