Growth Rate of the Brown Trout (Salmo trutta Linnaeus, 1758) from the River Iliyna, Bulgaria

The growth rate of the brown trout ( Salmo trutta ) from Iliyna River, Bulgaria was studied. The relation between the fish length (L) and scale radius (R) is described by the equation L=12.067R+1.4829, r=0.94. The relation between the length and the weight (W) is described from the equation W=0.0162L 2.9444 , r=0.999. With the increase of the fish age, the average annual increments are changing irregularly. The highest length increment occurs during the second year (6.71 cm) and the smallest during the fifth year (1.96 cm). The highest weight increment was established for the fourth year = 37.91 g. The population of S. trutta from Iliyna River has relatively fast temp of growth. The von Bertalanffy’s linear and weight growth equations are as follows: L t =23.16 [1-e -0.4666 (t-0.38) ], r=0.995, SD=6.8 and W t =160.692 [1-e -0.4978 (t-0.4164) ] 2 .94 , r=0.998, SD=7.15.