Masculinization of Oreochromis niloticus by androgen 17-a methyltestosterone and its effects on fish chromosomes

ملخص البحث

Tilapia species are of great importance in aquaculture in the tropics and subtropics that are especially suffering from a lack of animal protein. Among the vast number of Tilapia species, Nile Tilapia Oreochromis niloticus is the most common in aquaculture . The main problem in the worldwide Tilapia culture is the early sexual maturity before marketable size. Sexual maturity in females is associated with a decrease in the growth rate due to switching food assimilates from somatic growth to gonadal growth. Culture of monosex populations, preferably males, has long been recognized as the most effective solution to the widespread problem of early sexual maturity and uncontrolled reproduction in Tilapia culture . All male Tilapia populations have greater growth potential (20-40%) more than the mixed sex and parents. To date, this has been achieved through, manual sexing, direct hormonal sex reversal and hybridization. Generally, sex-reversal of Tilapia by hormonal treatment is the most successful technique. Male sex-reversal is achieved by administration of steroid androgens during the period of gonadal differentiation. Immersion, injection and feeding are the basic ways of administering sex-reversal hormones, but feeding remains the most practical method. The study aimed to: 1-Determine the optimum dosage and duration of 17 -methyltestosterone (MT) administration that interfere in the development of undifferentiated genetically female (XX) Nile Tilapia fry to be reversed to male (∆XX). The effects of the hormone on growth and survival characters are to be studied also. 2-Study the mutagenic effect of MT hormone on fish chromosomes by means of sister chromatid exchange analysis. 3-Investigate the effect of MT treatment on gene expression using electrophoretic techniques in the case of: a- Total soluble protein banding patterns. b- Esterase and Peroxidase isozyme profiles. The present investigation revealed that: - The highest percentage of males (97.5%) was obtained by using 60 mg MT/kg diet dose for 60 days feeding duration. -The MT treatment increase the means of sister chromatid exchange (SCE) frequencies per cell. - The MT treatment led to differential expression of the genetic information in Nile Tilapia, resulting in changes in gene products, including protein profiles. - The MT treatment induced the synthesis of certain proteins that not only differed from one tissue to another but also depended upon the duration of hormonal treatment.

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الكلمات الدلالية:

Masculinization - Oreochromis niloticus -androgen- fish chromosomes