Georgi Ivanov Zhelyazkov
The aim of the study was to determine the effect of the dietary betaine supplementation on the survival rate, weight gain and feed conversion ratio of rainbow trout (Oncorhynchus mykiss W.), cultivated in recirculation system. The fish were fed with extruded pellets “Aqua UNI“, with size 2 mm. Betaine in amount of 1% and 3% was added in the feed of the rainbow trout from the experimental groups EG1 and EG2 respectively, the control group (CG) received no betaine supplementation of the diet. In regards to the survival of the fish from different groups no discrepancies were observed. The average individual gain of the rainbow trout was as follows: CG-70.23 ± 1.42 g, EG1-71.93 ± 1.33 g and EG2-73.91 ± 1.30 g, the differences were significant (P<0.01). The best feed conversion ration had the rainbow trout from EG2 - 1.04 ± 0.01% and it was lower than that of the groups EG1 and CG by 1.07 ± 0.01% and 1.13 ± 0.02% respectively, the differences were significant (P<0.01). The economic conversion ratio of fish production in the groups, receiving 1% and 3% dietary betaine supplementation was identical 3.47, that is lower than these ones of the fish from control group by 4.32%.