Growth of perch Perca fluviatilis L., 1758 (Percidae) in the Kazakh part of the Ishim basin

The growth of Eurasian perch in water bodies within the Ishim River system in the Republic of Kazakhstan has been investigated. Data from 29 samples from various water bodies of the Ishim watershed and some adjacent watersheds are presented. The most extensive age series were found in specimens from Lake Lobanovo (National Park “Kokshetau”) – up to sixteen years (15+). River populations had a shorter lifespan. Comparison of growth rate patterns indicates the presence of two conditional “units”: the first includes the majority of lake populations, while the second includes Karatomarskoe Reservoir and Lake Lobanovo. Some samples are located outside of these groupings. The examined chronological samples show significant differences in growth for some. This is typical for Lake Karakol and, partialy, – the Ishimskoe Reservoir, where positive hydrological changes occurred between perch catches years, resulting in increased growth rates. These samples exhibit a low level of correlation in growth indicators between adjacent ages, indicating disruption in growth rate “canalization” and the acquisition of opportunities for individuals in a renewed unbalanced habitat environment. In relatively stable conditions of most other water bodies, the correlation level of these data indicators is high for the majority of comparison pairs. When comparing Ishim populations with previously published data on the Nura and Sarysu river watersheds re-garding growth rates, one can empirically conclude about the more successful growth of perch in the Nura-Sarysu watershed. However, it should be noted that mainly water bodies without commercial fishing and with developed recreational fishing were studied in the Ishim watershed. In contrast, water bodies with predominant commercial fishing were surveyed in the Nura-Sarysu system. The different impacts of these types of fishing may determine both the growth rates and the lifespan of perch.