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The effect of the temperature on the spawining phenology of the fish assemblages and the role of the exogenious and endogenious factors in temporal niche overlaping of fish assemblages were investigated in different water body types of the Dnipro River basin within the “Dnipro-Orilskiy" Nature Reserve (Ukraine in the years 1997-2018. The period of spawning (beginning and end) of the Blicca bjoerkna, Carassius gibelio, Scardinius erythrophthalmus, Abramis brama, Perca fluviatilis, Rutilus rutilus, and Esox lucius was estimated. Community niche overlap was estimated by calculating the pairwise Pianka index. The temperature was discused as an exogenous factor effecting on the fishes spawn timing. From 1998 to 2018 the average temperature in the study area continued to rise. The annual course of the temperature takes the sinusoidal waveform, which can be described by a fourth-degree polynomial. The residuals of the corresponding polynomial trend are specific for each year. The regular components of the residuals variation were revealed by dbMEM-variables. Fishes spawning occurred within the narrow water temperature ranges, which are specific for each fish species. There are statistically significant differences between ponds in water temperatures at which the spawning start occurred. The water temperature at which the spawning start occurred is linearly dependent on the time of the spawning start. There were temporal overlaps between spawning of the different species. The deviation of the Pianka mean niche overlap indexes from random alternatives does not depend on the habitat type. The decreasing trend of the Pianka mean niche overlap indexes was observed during the study period. There is no statistically significant correlation between the average annual air temperature and the level of the niche overlap. The degree of niche overlapping depends on broad-, medium-, and fine-scale temperature patterns.

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It was revealed that Gibel carp, Carassius gibelio (Bloch, 1782) spawning phenology is determined by regular patterns of variability in temperature and precipitation over the period of time after spawning in the previous year. The sensitivity to temperature of water as a stimulus to spawning was shown as being dependent on the characteristics of the environment and fish development trajectories over the previous year. Information about fish spawning was collected in the Dnipro-Orylskiy Nature Reserve in the following locations: Nikolayev system of water bodies, River Protoch system and the Obukhov floodplain, the channel of the River Dnipro, water bodies of the Taromske ledge. The materials that formed the basis of this research were collected from the waters of the reserve in the years 1997–2018. There are dependencies between the air and water temperatures that have their own characteristics depending on the type of water body. These dependencies are described by a logistic equation. The temperature regime in water bodies of the Taromske ledge is very similar to the temperature regime of Nikolayev system of water bodies. The difference is that the spring period of the temperature increase in water bodies of the Taromske ledge comes earlier – in late February – early March. The air temperature dynamics over the year is described by the fourth degree polynomial. The residuals of the polynomial regression for each year were subjected to principal component analysis. The principal component analysis allowed us to identify 8 principal components of the temperature regimes, which together describe 59.2% of the variation of the residual of the polynomial trend. Deviations from the linear trend of the precipitation are systematic throughout the year, reflecting the uneven nature of rainfall during the year. The residuals of linear trend regression models of cumulative precipitation can be used as indicators of the dynamics characteristic of precipitation during the year. The residuals were used for principal component analysis, which revealed that the dynamics of the precipitation can be divided into five orthogonal principal components. The first five principal components explain 82.6% of the feature space variation. The timing of the onset of C. gibelio spawning in 95% of cases occurs on the 113–139th days of the year (on average, it takes place on the 125th day). Regression analysis revealed that the climate principal components and types of the lake systems can explain 79% of the variation in the timing of the onset of C. gibelio spawning. The water temperature at the time of C. gibelio spawning was exposed to natural dynamics in year aspect. The local minimum of the onset of spawning temperatures occured in the mid 2000s. Total of 69% of the water temperature variation at which spawning begins can be described by climatic predictors and water biotope types. The variation explained by some temperature principal components may be increased considerably after including as covariates such variables as the precipitation principal component and the biotope type. This principal component which represents the high frequency variation of the air temperature regime with a characteristic period 20 and 45 days has the highest explanation ability of all the components and is a constant explanatory predictor for all considered spawning characteristics.

This paper describes spawning events of the white bream Blicca bjoerkna (Linnaeus, 1758)in astronomical and biological time depending on seasonal patterns of climatic conditions. The research was conducted in the "Dnipro-Orilskiy" Nature Reserve (Ukraine) during the years 1997-2015 in four habitat types. The timing of the spawning event (start, end) was evaluated using astronomical time (number of days from January 1 each year), with correction for the lunar and the semilunar cycle, and using biological time (number of days from the end of spawning in the previous year to the beginning and end of spawning in the current year). The spawning phenology of the white bream was found to be dependent on the dynamics of weather conditions over time. Patterns of varying climatic regimes which are expressed by means of multivariate principal component are the most informative predictors of the spawning events. Evaluation of occurrence of spawning events in astronomic or biological time gives somewhat different models of the impact of climate regimes. The impact of the principal components indicating variability of rainfall during the year in which spawning occurs is statistically significant for almost all regression models. Models using the solar calendar are also more sensitive to the course of air temperatures within the year when spawning occurred. Correction of time based on the lunar cycle allows us to assess events which are sensitive also to the temperature and rainfall variation during the second half of the previous year. Biological time was shown to be sensitive to environmental influences over time from the end of spawning in the previous year to spawning in any given year.