Telomerase activity has been found in the somatic tissues of rainbow trout. The enzyme is essential for maintaining telomere length but also assures homeostasis of the fish organs, playing an important role during tissue regeneration. The unique morphological and physiological characteristics of triploid rainbow trout, when compared to diploid specimens, make them a promising model for studies concerning telomerase activity. Thus, in this study, we examined the expression of theTertgene in various organs of subadult and adult diploid and triploid rainbow trout females. UpregulatedTertmRNA transcription was observed in all the examined somatic tissues sampled from the triploid fish when compared to diploid individuals. Contrastingly,Tertexpression in the ovaries was significantly decreased in the triploid specimens. Within the diploids, the highest expression ofTertwas observed in the liver and in the ovaries of the subadult individuals. In the triploids,Tertexpression was increased in the somatic tissues, while the ovaries exhibited lower activity of telomerase compared to other organs and decreased compared to the ovaries in the diploids. The ovaries of triploid individuals were underdeveloped, consisting of only a few oocytes. The lack of germ cells, which are usually characterized by highTertexpression, might be responsible for the decrease in telomerase activity in the triploid ovaries. The increase inTertexpression in triploid somatic tissues suggests that they require higher telomerase activity to cope with environmental stress and maintain internal homeostasis.