THE NUTRITION OF A BROWN TROUT Salmo trutta m. fario IN THE RIVER UNA

An analysis of the contents of gastric–intestine system of a brown trout was made on the base of the capture 103 specimens in the aim of the description of its nutrition. The capture was made at the 15 places in the confluence of the river Una, commune Bihac, by generating sets and sacks. The dissection of a brown trout, extraction of gastric–intestine system and its fixation in 4 % formaldehid was made at the terrain. Further treatment and examination of the contents of gastric–intestine system was made in the laboratory of Ichtiological and Fishing Center of Faculty of Science, University of Sarajevo. The obtained results of the analysis of the nutrition of a brown trout are particulary similar with the literature data (Mc Cormac, 1962; Elliot, 1967; Šenk and Aganović, 1968; Tuša, 1968; Kaćanski and Kosorić, 1970; Popovska — Stanković and Georgiev, 1973; Kaćanski et al., 1988). On investigated places, the specimens of a brown trout dominantly fed by macroinvertebrat of the benthos of the bottom. The large percentage of fish use larvae stages of the two–winged insects (45,45%) and caddisflies (42,42 %) in their nutrition. The small number of fish fed with bullhead (7,07 %). Great dependence was determined in the nutrition of a brown trout by qualitative–quantitative composition of the benthos (Trožić–Borovac, 2001). The very small number of fish fed with algae (1,01 %). According to these results, we can conditionally speak about zoofag. The specimens with empty stomach, but very good developed gastric–intestine system, was also registrated (4,04 %). This data is related to the time of the capture (the season of reproduction of brown trout when it takes less food). The condition factor was calculated for all the specimens of brown trout. The values of the condition factor are from 1,00 to 1,59. According to the average weight 21,77 g and average leingth 133,37 cm the condition factor for the analyzed fish from the confluence of the river Una is 1,09.