G. Zheliazkov*

Department of Biology and Aquaculture, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria

Abstract. The aim of this study was to determine the influence of linseed and sunflower oils in the diet on the survival rate, weight gain and the feed conversion ratio in rainbow trout, reared in a recirculating system. The fish of the three groups were raised in concrete tanks with effective capacity of 0.8 m3, which were part of the recirculating system. Rainbow trout received extruded feed (6 mm pellets), produced by “Aqua garant”. The feed of the fish from the experimental group (EL) was supplemented with 5% linseed oil, while that of the trout of the group (ES) – 5% sunflower oil. The diet of the fish of the control group (C) did not contain any of the above mentioned oils. The duration of the trial was 60 days. In order to study the effect of linseed and sunflower oils in the diet on the weight gain of the fish, control catches were carried out at 15 days’ interval. The live weight (g) and linear growth (mm) of the control catches were determined as the fish were individually weighed and measured. The final live weights of the trout in the experimental groups as well as that in the control were as follows: EL – 334.79±67.52g, ES – 329.39±70.31 g and C – 323.58±67.77 g. The values of this parameter in EL were higher than those of fish from ES and the control group by 1.64% and 3.47%, respectively, but the differences were not significant (P>0.05). This trend persisted also for the linear measurements – in the trout of EL they were the highest. The fish of EL displayed the lowest feed consumption. This trait had lower values than the ones of the trout of ES and the control group by 2.84% and 5%, respectively, though the differences were not significant (P>0.05). The survival rate of the fish from the groups did not differ substantially.