Age structure, growth rate and condition factor of Squalius orpheus (Cyprinidae) of Maritsa river’s middle zone, Bulgaria

Abstract

Age, growth and condition factor were determined for Squalius orpheus of the Maritsa River’s middle zone. A comparison was made of length differences for the same age group of stream and reservoir populations. A total of 114 S. orpheus were caught and examined. The fish were classified in six age groups (1-6 years). One-year-old fish dominated the samples. Standard body lengths (SL) ranged from 3.4 to 30.5 cm and the length of the majority of the samples was between 5.0 and 7.0 cm. A length-weight relationship was described as W = 0.000009∙SL^3.0934, (r² = 0.9796, P < 0.05). Length growth was expressed as SL = 2.1554S+16,588, (r² = 0.9927, P < 0.05). Condition factors and the coefficient from Fulton’s equation ranged from 1.26 to 1.53, with a mean value of 1.28. Fulton’s coefficient increased from one-year-old to five-year-old fish. The present study of Orpheus dace’s population parameters contributes to the knowledge of the species’ population biology.