Burbot (Lota lota L., 1758) Larval Distribution in the Streamflow during Long Downstream Migration

The article presents long-term (from 1996 to 2018) data on the distribution of burbot larvae at the endogenous-feeding stage during downstream migration in a stream of spawning tributaries of the Ob River: the Severnaya Sosva River (16 years of observations), the Sob River, and the Voikar River (one year of observations). The assumption that the predominance of larvae in the flow horizons depends on the flow velocity has not been confirmed; the distribution depends on the developmental stage. Based on the Spearman correlation and the Mann-Whitney criterion, the developmental stage of downstream migrating larvae at the control point, mediated by the distance of downstream migration, is shown to depend on the maximum level of floodplain flooding per year of prespawn migration of the spawners. Before the start of the physiological functioning of the swimming bladder, juveniles are more common in the lower horizons of the stream; after the start, they are more common in the upper ones. Immediately after hatching, due to the presence of a rheoreaction and negative geotaxis, the larvae use their muscles to enter the zone of active turbulence, which is the main factor contributing to their maintenance in the water column in the first three days of life.