Population characteristics of freshwater bream Abramis brama in the Novosibirsk reservoir (Western Siberia) 60 years after introduction

Freshwater bream Abramis brama is the most successful alien fish species in the Ob basin. It was introduced into the Novosibirsk Reservoir immediately after the formation of the reservoir, in the late 1950s. It quickly became numerous, and since the 1990s it has accounted for up to 90% of fish catches. Over the 60 years since the introduction of the species, its population characteristics have changed. The lifespan of fish has increased to 16 years, while their size characteristics have decreased, especially in older individuals (weight by an average of 19%), which may be due to the increased number of the alien mollusk Viviparus viviparus, which worsens feeding conditions. The largest bream recorded in the Novosibirsk Reservoir had a commercial length of 57 cm and a weight of 5540 g. Compared to the first years, bream began to reach sexual maturity at an older age, but with a similar standard length and weight of individuals. The onset of spawning is noted at a water temperature of 8 ° C and, compared to previous periods, has shifted to an earlier date (the first ten days of May), which is obviously caused by an increase in the temperature background in the region. Bream fecundity has significantly decreased, which may be due to the known effect of fish density on their fecundity, and at present individual absolute fecundity ranges from 76.8 to 385.1 thousand eggs (an average of 187.85 thousand), and relative - from 103 to 269 eggs (an average of 166). Absolute fecundity is closely related to the body weight of females (r = 0.852). At present, the population characteristics of bream, reflecting the life strategies of fish, are generally close to the parameters of the populations of this species from the central part of its native range.