The effects of COX-Inhibitors (Diclofenac and Ibuprofen) on growth rate, mortality and sexreversal in Nile Tilapia (Oreochromis niloticus)
Al-Qutob, Mutaz A.
Nashashibi, Tharwat S.
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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.