Morphological characteristics of bream Abramis brama (Linnaeus, 1758) of the Penza (Sura) reservoir

Background. The biology of bream and a number of other main commercial fish of the Penza (Sura) Reservoir has been studied quite well. The exception is the description of the morphological features of fish, the study of which requires a certain amount of fresh field material, which is quite difficult to collect in the absence of commercial fishing. The purpose of this work is to begin filling the gap in ichthyological studies of the region using the methodology we propose – to describe the morphometry of the bream of the Penza Reservoir and clarify its place among other bream populations in the country. Materials and methods. To collect the material, we used a modern method of photo documentation adapted by us directly for working with bream. The selection of material was carried out from net catches on the Penza Reservoir from 09/01/2023 to 04/01/25. A sample of 30 specimens with a body length of 21.5–49.0 cm was used for the article. Photo documentation was carried out with Canon Power Shot A3100 IS and Nikon COOLPIX A cameras. Measurements on the fish body were made with a ruler on printed images in A4 format for the purpose of double-checking them, a small number of measurements on the fish head were made in the Image J program on the computer screen. The number of rays in the fins and scales in the lateral line was counted on the computer screen. The material was processed using traditional methods, taking into account the requirements for measurements of morphological features for carp fish. Results. The fin formula of the bream from the Penza Reservoir is D III 9 (7–10), A III 25 (24–27)). Single-row pharyngeal teeth – 5–5, 5–6. The number of vertebrae with urostyle is 44–45 (cf. 44.8). The number of gill rakers is 21–26 (cf. 23.3). A high coefficient of variation of the characters is noted for the greatest height of the anal fin, the distance between the ventral and anal fins, the snout length and the eye diameter. Of the 25 plastic characters in males and females of bream, reliable differences were found in four. For two characters: the height of the anal fin, the distance between the pectoral and ventral fins, the differences had a high significance level of -0.01, the t-criterion, respectively, was -3.4 and 3.9. In comparison with the populations from the Oka, the Pripyat and Lake Ilmen bream of the Penza Reservoir is distinguished by the greatest body depth, short postdorsal distance, long base of the anal fin, large distance between the pectoral and pelvic fins, smaller distance between the pelvic and anal fins, short snout, long postorbital part of the head, narrow forehead. This is due to the small size of the Penza Reservoir with no current and low degree of siltation. Conclusions. The morphological characteristics of the Penza Reservoir bream are presented. According to the traditional classification, it occupies an intermediate position between the typical bream (of the Baltic basin) and the eastern bream (of the Caspian Sea basin). According to Yu. G. Izyumov (1987), the Penza Reservoir bream can be attributed to the central geographic group of populations. According to A. V. Kozhara and A. N. Mironovsky (1988), to the Middle Volga group.