Effects of the Aromatase Inhibitor, Letrozol, on Levels of Serum 17β-Estradiol (E2) And Enzymes in Rainbow Trout (Oncorhynchus Mykiss Walbaum) Females

In the present study, changes of values of serum 17ß-estradiol (E2), Asparate amino teransferase (AST), Alanine amino transferase (ALT) and Lactate dehydrogenase (LDH) following intraperitoneal (i.p) injection with the aromatase inhibitor (AI) letrozole were investigated in rainbow trout (Oncorhynchus mykiss). Forty- eight apparently healthy rainbow trout (mean weight of 845 g) divided in four groups (twelve fish for each group). (1) Control vehicle injected, (2) group treated once with 1.0 mg AI kg-1, (3) group treated once with 2.5 mg AI/ kg and (4) group treated with 2.5 mg AI/ kg weekly (3×2.5 mg AI/ kg. Results revealed that that, in the group injected weekly, serum E2 levels were significantly (P< 0.05) lower than the other groups. Also levels of serum enzymes at days 14 and 28 of injection, significantly increased in the group injected weekly compared to the other groups (P< 0.05). No significant differences have been observed between control and the groups injected once in respect to all parameters (P> 0.05). This study showed that multiple injections with letrozole may decrease E2 levels and may impact negatively on the physiology of the fish as manifested in changes in some of serum enzymes under laboratory conditions