Paper Title
Impact of Increased Water Temperatures on Sex Determination in Fish: Proposed Impact of Global Warming Effect

Abstract
Fishes are the most abundant vertebrates on Earth, showing great diversity of species (27, 977) unmatched by other classes and exhibiting a large variety of mechanisms of sexual determination (SD) the event that compromises a bipotential gonad to develop as an ovary or a testicle. The processes of sexual determination and differentiation in fish are highly plastic and influenced by factors such as pH, temperature, and social conditions etc. A simple unifying model to explain the genetic basis of sex determination in fishes does not exist since the phenotypic sex may not always confirm to the genotypic sex. A wide spectrum of reproductive strategies exists in fish ranging from strict gonochorism to hermaphroditism and temperature is projected as the main environmental determinant of sex through a process called temperature-dependent sex determination (TSD). Thus given the growing concern of global warming, studies on the effect of temperature on several aspects of sex differentiation in fish and ecological balance are given more attention recently including. Zebrafish that have a maximal thermal tolerance range 6.2°C - 41.7°C are classified as Eurythermal and 28.5°C of water temperature is widely cited as the optimum temperature for zebrafish growth and breeding. Aromatase is an enzyme that catalyses the conversion of androgens to estrogens and play a pivotal role in temperature - dependent sex determination of several poikilotherms. Though considerable work was done on sex-differentiation and aromatase expression in teleosts, less attention was paid to understand the effect of higher temperatures on aromatase gene expression. Hence this study is focused to assess the influence of increased water temperature on gonad sex differentiation in early juveniles and the role of expression of aromatase gene in a model organism zebrafish, Danio. albino Exposure of Post hatching (days post hatching-dph) juveniles to 32 / 36 ± 0.5 ° C for was found to result in gonad transition in more than 50% of the population providing evidence of apoptosis or the disappearance of oocytes / ovarian cavity and transition of ovary to testes along with reduced . expression of aromatase. More than 50 % of individuals differentiated to males at high temperatures indicate that lack of aromatase which is the precursor for estrogens leads to non formation./reduced of female gonad. This is further found to lead to deviation in sex differentiation. Post harvest juveniles aged 22/32/42 days upon exposure to 32 ± 0.5°C exhibited Phenotypic sex males and female ratio of 68:32 / 56:44 / 48:52 respectively. But the same groups upon exposure to 36 ± 0.5°C showed the ratio of the same as 98:2.0 / 72:28 / 53:47 respectively compared to that of 50:50 in controls maintained parallely at 26 ± 0.5°C. But genotypic sex analyzed through RAPD using sex-specific primer OPA 14 showed the male : Femlae sex ratio as 5:5 and 6:4 at 32 / 36 ± 0.5°C respectively similar to the control group. Hence it is clearly found that early juveniles when get exposed to temperature increase by 4 to 8 ° C during thermosensitive period even for only 72hrs will suffer from variation in sex differentiation resulting in the generation of more phenotypic males which are in other terms originally genotypic females. Thus this study clearly conveys an alarming sign that high water temperatures associated with global warming boud to cause a significant impact and variation in the sex ratio of fish population or for that matter any aquatic animal which may lead to greater ecological imbalance.