(Bioflux - bimonthly, 2009-10-30) Al-Qutob, Mutaz A.; Nashashibi, Tharwat S.
Several studies have been conducted to detect the direct effect of inhibiting the aromatase
activity, the rate limiting enzyme that converts androgens to estrogens needed for ovarian differentiation
in fish to overcome the immediate need for a more environmentally friendly substitute of methyl
testosterone. Cyclooxygenase (COX)-inhibitors are potent and irreversible inhibitors of the COX pathway
and since studies on human breast cancer cells shows that they decrease aromatase messenger
ribonucleic acid (mRNA) expression at the transcriptional level we tested the hypothesis of possible
aromatase inhibition by the non-selective COX-inhibitors in fry fish tilapia. The effects of supplementation
of COX-inhibitors (diclofenac and ibuprofen) in the diets of tilapia on growth rate, mortality and sexual
differentiation have been studied. 20 Genetically females (XX) (O. niloticus) larvae were stocked in
triplicates in a closed system and each were given control diet (C group) and control diet supplemented
with (10 mgKg-1) diclofenac (1% diclofenac group), (5 mgKg-1) ibuprofen (0.5% ibuprofen group), and (5
mgKg-1) (0.5% diclofenac group) respectively for 4 weeks. After the 4th week all diets were changed to
control diet. At the end of 12-weeks, no significant differences were found in growth rate (GR) between
diets (p>0.05). Mortality ranged from 1.67% +- 2.89 (SD, n=3) in control group to 58.3% +- 14.4 (SD,
n=3) in the 1% diclofenac group during the experimental feeding and from 6.67+-2.89 (SD, n=3) to
63.3%+-10.4 (SD, n=3) at the end of 12-weeks period. 7% In the control group, 36% in the 1%
diclofenac group, 17% in the 0.5% ibuprofen group, and 22.2% in the 0.5% diclofenac group
respectively never produced egg during the entire experimental period. Macroscopically all the nonspawning
fish in the experimental groups were females with apparently larger ovaries and full of eggs
compared to control. Microscopically they were full of apparently normal eggs with morphology similar to
those of control. Postulated mechanisms of action of the supplemented COX-inhibitors are discussed.
Based on the above it can be concluded that the use of COX-Inhibitors during the crucial period could
modulate aromatase activity and affect reproduction in Nile tilapia.