This study estimates the dependence of the duration of the downstream migration of burbot larvae in the Voikar River (the Lower Ob basin) on the relative condition factor of semianadromous spawners...

The results of long-term observations on changes in the hepatosomatic index of burbot in the Lower Ob basin are presented. The dynamics of this index are considered as dependent on fish sex, stage of gonad maturity, period of reproductive cycle, body damage or abnormalities, and feeding intensity.

The results of long-term observations on changes in the relative body conditions of burbot (Lota lota L.) in the Lower Ob basin during the open channel period (June–September) are analyzed. Statistically significant strong positive dependence of the hepatosomatic index of spawners on the maximum flood level is revealed. An equation predicting the value of the hepatosomatic index of spawners from instrumentally measurable environmental parameters is constructed.

The generation abundance of peled has been assessed at the lower reaches of the Ob’ River. Based on data on the number of larvae migrated downstream from spawning grounds, obtained in 1981–2021 on the main spawning rivers, current population structure of peled at the lower reaches of the Ob’ River is described, the influence of anthropogenic factors and of the water content of the Ob’ River floodplain on peled reproduction is analyzed. The Severnaya Sos’va River definitely plays a decisive role in the reproduction of peled. In recent years, there has been an increase in the contribution of the Voikar and Sob’ rivers. Seven-year cycles have been identified (between the peaks in the larvae number); their maximums coincide with the peaks of water content at the lower reaches of the Ob’ River with a 1-year lag, which supports the world’s largest river peled population abundance. The presence of such cycles makes it possible to predict phases of high fish abundance. An equation describing the dependence of the generation size of peled at the lower reaches of the Ob’ River on the average water level of Ob’ River in June–August at the Salekhard gauging level in the previous year is proposed.

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...