Comparison of Lesser galangal, Alpinia officinarum extract and Letrozole in masculinization of Nile tilapia, Oreochromis niloticus

Introduction: The ability to control sex is one of the most important commercial and efficient factors of the aquaculture industry. Sex reversal and sexual maturity control are among the most important goals of hormone induction in aquatic animals. Plants can be used as a potential alternative to chemical compounds in aquaculture. Alpinia officinarum is a plant from the ginger family, which is native to China. Since the use of plant extracts in aquaculture is a new approach, there is no definite standardization in almost all aspects of plant extract administration and use. So, the purpose of the present study was to investigate the effects of different doses of the rhizome extract of A. officinarum on the sex reversal of Nile tilapia fry and compare it with the chemical drug, letrozole.
Materials and Methods: The number of 2760 pieces of Nile tilapia larvae seven days after fertilization with an average weight of 0.026 ± 0.002 g distributed in 24 aquaria (200-L in volume) equipped with aeration and filtration systems in equal and completely random released. Larvae were tested for 30 days. Masculinization of larvae using the combination of letrozole aromatase inhibitor and ethanolic extract of the rhizome of A. officinarum, in eight treatments including two control treatments (control, without additives and solvent, impregnated with ethanol); three experimental dietary treatments including  ethanol solution of 200, 300 and 400 mg/kg of letrozole followed by ethanolic extract of the A. officinarum rhizome in three experimental treatments including 200, 300 and 400 mg/kg, each with three repetitions. Whole-body and ELISA methods were used to measure the testosterone hormone. The squash method was used to determine the sex of fish larvae. The growth parameters, survival, sex determination and gonadosomatic index were measured. One-way analysis of variance and Duncan's test were used to investigate the significance of supplementing by additives at the 0.05% level.
Results and Discussion: According to the results, the lowest level of testosterone was observed in the control treatment (0.116 ng/g) while the highest in the 400 mg treatment (0.475 ng/g; p<0.05). The highest and lowest male and female percentages were revealed in Letrozole (400 mg/kg) (p<0.05). According to the results, the lowest final weight and specific growth rate at the end of 30 days were observed in the control and solvent treatments, while it was the highest in the treatments containing A. officinarum (p<0.05). The lowest and highest FCR and gonadosomatic index at the end of the experiment were observed in treatments with 300 mg/kg and 400 mg/kg, respectively (p<0.05). No significant difference was observed in survival rate among all experimental groups (p>0.05). In the present study, the percentage of males increased by elevating dose of A. officinarum and letrozole. The obtained results clearly showed that the A. officinarum has significant effects on reducing FCR and final weight. Based on the results, treatment of 400 mg/kg can upraise the testosterone level and the rate of masculinization in tilapia fry.
Conclusions: Given the positive response of the ethanolic extract of A. officinarum rhizome with a dose of 400 mg/kg in creating male in tilapia fry around 92% and significant superiority in weight indices, SGR, FCR and gonadosomatic index compared to letrozole treatment, it can be used to produce single-sex male Nile tilapia. In addition, it is possible to achieve a higher percentage of the male population using a dose of over 400 mg/kg, which was not available in the present study and requires further studies.