Features of the development of juvenile Aspius aspius (Linnaeus, 1758) from different biotopes of the Ile river delta

Abstract

Aspius aspius is an important commercial fish species introduced into the basin of the Balkash Lake. The
developmental biology of juveniles of this species is poorly understood. In addition, the reactions of juvenile fish to various
human impacts on natural water bodies are poorly studied. The purpose of the study conducted in 2018 was to assess the
conditions for the development of juvenile A. aspius in the Ile delta. Morphological and biological analyzes were performed
according to the traditional scheme. The fluctuating asymmetry of bilateral signs was also studied. The states of 11 countable
and 14 plastic signs were studied. Population diversity was assessed using the principal component method. Juveniles of different
ages were found in the Ile river section above the delta, and the juveniles of the first year of life live only in the ducts. The growth
of juvenile A. aspius in the delta of the Ile river occurs much more slowly than in the rivers Volga, Ural and Syrdarya. The
values of the As coefficient of fluctuating asymmetry in the studied fish indicate significant disturbances in the homeostasis of
individual development. Among the studied individuals of A. aspius, phenodeviates were found — individuals with a shortened
(pug) snout. Plastic and countable signs of juveniles are characterized by great variability beyond the limits known for this
species. In general, the state of the habitat was assessed as unfavorable for the development of juveniles.