BIOLOGY OF PONTOGAMMARUS ROBUSTOIDES (G.O. SARS, 1894) (MALACOSTRACA: AMPHIPODA: PONTOGAMMARIDAE) FROM LAKE VISHTYNETSKY IN 2018–2019

Pontogammarus robustoides ‒ a Ponto-Caspian species important in bottom hydrobiocenoses, including Lake Vishtynetsky in the Kaliningrad region, having glacial origin. Analysis of 462 individuals showed a difference in sexual composition (equal sex ratio in November 2018 and dominance of females by 1.5 times in April 2019); juvenile individuals were not encountered. The total body length of individuals was 3.5-17.1 mm; males reached larger sizes than females, but their predominant sizes were close. Females nonbearing eggs (3.5-14.6 mm) were numerically dominant among females. Females in April 2019 carried embryos in early stages of development; the first spawning size was 8.6 mm. The beginning of spawning season was late March to early April. Fecundity reached 60 eggs; length of newly laid eggs was (0.4-0.6) × (0.3-0.54) mm.