Sexual Transformation in the Swordtail Fish Xiphophorues helleri under the Influence of Hydrocortisone Hormone and Temperature

Abstract

Background: Sex in vertebrates is generally determined by two mechanisms: Genetic Sex Determination (GSD) and Environmental Sex Determination (ESD). ِAim: This study evaluated the identification of sex in fish by external factors such as temperature, as well as the role of hormones, such as corticosteroids. The mature Xiphophorus helleri were obtained from aquarium fish shops in Basrah Governorate. The experiments were designed by conducting two experiments involving 40 fishes, the first was in the summer from 30 July 2017 to 28 August 2017 under laboratory temperature (2837C°). The water temperature was between (2834C°) and 14-hour lighting. The second experiment was in the winter from 3 December 2017 to 2 January 2018 under laboratory temperature (17-21C°) and a water temperature between (16-21C°) and an 11 hours lighting. The mature fishes were divided into two groups, each containing 20, 12 female (1.63g) and 8 male(2.72g), placed in 60-litre glass basins with ventilators and thermometers to measure the water temperature. The first was considered as a control group for both the summer and the winter experiments. The second group was treated for a month with the Hydrocortisone Sodium Succinate (Roxcortisone) with a concentration of 2.5 mg /l. Results: Showed that the phenotypic changes in the female X. helleri treated with Hydrocortisone and temperature (2834°C) and (16-21°C) were caused by gradual elongation of the ventral part of the caudal fin, where the elongation reached the significant limit (6.08±0.031.52±0.83) between females treated in the summer and winter groups respectively and the females of the control group. There was also elongation in the female groups treated in summer and winter but did not reach the significant limit at the probability level (P≤ 0.05). As the results of the microscopic examination for the ovaries of X. helleri treated with Hydrocortisone and temperature (2834C°) showed the presence of some ovaries containing large numbers of atrophy eggs, ovaries containing lysis embryos and eggs, while other ovaries contained complete growth embryos but dead. As for the ovaries of other female group treated with Hydrocortisone and the temperature of (16-21Co), they were characterized by containing many embryos which are dead and some of them appeared with various congenital malformations, such as those with a puffy head in the cavernous region. It was also noted that some embryos had sprains in different areas of the spine. Conclusion: The hydrocortisone act as a promote to sexual transformation under different temperatures. This sexual transformation is done on one of the external features only, that is the emergence of the sword in females. Received: 21 June 2019, Accepted: 20 September 2019