Supplement 1 Ecological Engineering and Environment Protection, IX, 2017, p. 56-65 56 AGE-SIZE STRUCTURE AND GROWTH RATE OF THE EUROPEAN CHUB (SQUALIUS CEPHALUS L.) IN LESNOVSKA RIVER, BULGARIA Galerida Raikova-Petrova, Desislava Rozdina, Margarita Kamenova Abstract: The population of the European chub (Squalius cephalus L.) from Lesnovska Rier consists 1 to 5 years old fish. The most abundand is the first age group (45,8%). The largest in size is a 5 years old individual with body length 235 mm and body weight 476 g. First and fifth age groups exibit highest size range. The following size groups are the most numerous: 7,1-8; 8,1-9 and 18,1-19 cm. The relation between the fish body length (L) and the scale radius (R) is described by the equation L=2,504R + 0,233; r=0.99. The von Bertalanffy’s linear and weight growth equations are respectively: L t =76.6 [1-e -0.0677 (t+0.419) ], r = 0.999 and W t = 7164, 5 [1-e -0.0698 (t+0.4686) ] 3,036 , r= 0.999. Based on the Hohendorf’s coefficients (L max : L ∞ = 0,38 and W mах :W ∞ = 0,07) it is established that the studied population doesn’t sufficiently use its growth potential due to overfishing of the largest individuals. The condition factor defined by the Fulton’s equation is 2.98. More precise methods to determine the condition of the population is to use the exponent from the relation L/W instead of the exponent 3 in the equation of Fulton, or to calculate the weight at one and the same length. Key words: Squalius cephalus, age-size structure, growth rate, Lesnovska River INTRODUCTION The European chub (Squalius cephalus L.) is one of the most widespread species from Cyprinidae Family. Its plasticity in relation to the biotope makes the species usual inhabitant of both the dams' ecosystems and the middle stream of the river. It is within preferd species for sport fishing. Lesnovska River is a right tributary of Iskar River. Its length is 65.2 km and its catchment area is 1096 m². Currently there are no published data on the biology of the European chub in Lesnovska River. The aim of thе study was to define the age-size structure and the growth rate of the population of the European chub from Lesnovska River. MATERIALS AND METHODS The material was collected in the end of September 2016 in the area of Negovan villae. The sculpture of 530 scales from 72 specimens was analysed. Sampling was done within one kilomether stretch of the river between the coordinates N 42 о 45` 328``; E 23 о 25` 038`` and N 42 о 24` 974``; E 23 о 09`014`` (Fig. 1). Fig. 1. Sampling area on Lesnovska River