Морфологічна структура популяції окуня гирлової ділянки річки Віти

Abstract

Питання існування в популяції окуня звичайний Perca fluviatilis (L.) різних екоморфологічних груп залишається спірним і усталеного погляду на нього не існує. Дані про різні екологічні форми окуня були відомі ще з початку 20-го століття [1]. Проте не всі дослідники погоджуються з цією думкою [2]. На сучасному етапі для деяких водойм [5] відмічена диференціація окуня на окремі морфологічні групи. Для басейну Дніпра подібних досліджень не проводилось.

В статье приведены данные относительно морфологической структуры популяции окуня устьевого участка р. Виты. Показано, что популяция окуня состоит из групп медленно- и быстрорастущих особей.

Numerous researches were devoted to study of perch Perca fluviatilis biological characteristics, growth rates and morphological indexes in general, but there is little information available on its ecological population structure. The paper describes the results of investigations of morpho-ecological structure of perсh population over 2013–2016 in the mouth area of the Vita River including Kozacha arm. The Vita River is the right tributary of the Dnipro River and Kozacha is its arm. Both water bodies serve as important spawning area, fattening and habitat for different fishes. The considered water area is characterized by variety of the water bodies’ types with different ecological conditions, including water exchange, velocity of flow, dissolved oxygen content, food base, which are more favorable in the Kozacha arm, and presence of coastal vegetation, which is more abundant in the mouth area of the Vita River. Sampling was carried out from November 2013 to August 2016, more intensively over the spawning season of fish in the mouth area of the Vita River and Kozacha arm. Totally 182 specimens were caught with gill nets of the mesh size 16, 20, 25, 35, 45 and 55 mm. The detailed analysis of morphological indexes of perch has been presented. All morphological indexes (Pravdin, 1966) and sex were determined for each individual. Age of individuals was determined by number of scale annuli (Chugunova, 1959). Studies were carried out using standard ichthyological methods and statistical analysis. Growth rate was calculated directly from the measurements of average age. The Student’s t-test was used for comparison of morphological parameters of specimens of different age groups, for males and females of the same age groups and for groups with different growth rate. Maximum observed age of perch in the mouth area of the Vita River was 6 years. Predominance of age classes 2–3 (9.0–11.0 cm and 16.64–26.00 g) in the catches was noticed. Mean value of standard length was 11.6 cm and mean value of weight was 36.37 g. In general, individuals of perch of the mouth area of the Vita River were characterized by small body size, low growth rate and short life duration. On the contrast, all examined specimens of perch of the Kozacha arm were characterized by larger body size, fast growth rate and longer life duration. Maximum observed age of perch in the Kozacha arm was 7 years. Predominance of age classes 3–5 (16.1–22.7 cm and 95.58–312.86 g) in the catches was observed. Mean value of standard length was 19.6 cm and mean value of weight was 203.92 g. The data obtained showed the low level of age and size variability in groups of perch with different growth rate. Morphological indexes l, lD1 in sample of perch with low growth rate increased in high age classes, whereas do, hc1 decreased. The comparison of males and females showed that on the whole females had higher indexes l, H, hc1 and lower indexes do, pl. In group of perch with high growth rate elder age groups differed significantly from junior age groups by values l, H, lA, which in older groups were higher, and do, which was lesser. Sexual dimorphism was low expressed. Value of pl of 5-year-old females was lesser than in males of the same age group. Comparison of groups of perch with different growth rate showed marked differences between specimens of same age classes. Individuals of higher growth rate differed by higher values of morphological parameters l.l., Squ1, l, aA, PV, PA and lesser values of P, h, lV, do in the same age classes. The analysis of the data indicates that population comprises two morpho-ecological groups, which differ by growth rate. Perch of the mouth area of the Vita River was characterized by small body size, low growth rate and short life duration. At the same time perch of the Kozacha arm was characterized by larger body size, higher growth rate and longer life duration. Age and size variability and sexual dimorphism were low expressed in both morpho-ecological groups of perch and could not influence results of morphological analysis.