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Göttingen, Germany

Wessels S.,Aquaculture and Water Ecology | Samavati S.,Aquaculture and Water Ecology | Horstgen-Schwark G.,Aquaculture and Water Ecology
Aquaculture | Year: 2011

The phenotypic sex in Nile tilapia is determined through major and minor genetic factors as well as environmental factors, such as temperature. Temperature treatments at 36 °C applied from 10. days post fertilisation for at least 10. days are known to influence the phenotypic sex. Recently a second window of temperature responsiveness was identified. Early rearing temperature (34-36 °C) applied from 12-52. h post fertilisation proved to exert an effect on the phenotypic sex in all-female progenies (XX). To study a possible correlation between the effect of early (12-52. h post fertilisation) and late [10-20. days post fertilisation (dpf)] temperature treatments on the phenotypic sex Nile tilapia, the present study investigates the influence of early rearing temperatures using mixed sex (XX/XY) progenies with predefined temperature responsiveness for the period from 10-20. dpf.The brood stock which produced the progenies for this experiment was derived from families of selected lines showing a strong or weak responsiveness of the male proportion towards a temperature treatment of 36 °C from 10-20. dpf. Sires and dams were chosen for the present experiment if the sex ratio in temperature treated groups showed male percentages of > 90% in the high-line and < 60% males in the low-line. Three progenies obtained from each line were subjected to an early temperature treatment at 34 °C, 35 °C or 36 °C starting at 12. h post fertilisation, whereas the corresponding full sib control groups were kept at 28 °C throughout the experiment. The experimental temperatures were reached within 5. h and were applied until hatching (52 ± 3. h). Temperatures above 34 °C led to total mortalities in all progenies tested (n=. 12 batches), whereas temperatures of 34 °C allowed survival rates that were comparable to those of the controls after nine. days, except for progenies from the high-line. Irrespective of the line the progenies belonged to, the sex ratios were not affected by the early temperature treatment starting at 12. h post fertilisation. In conclusion, the temperature responsiveness towards early and late temperature treatments seems not to be correlated and might be dependent on the genotypic sex of the progenies. More studies are needed including information on the temperature responsiveness during both stages (before hatching and during sex differentiation), the genetic sex of the offspring, timing of temperature treatments as well as pedigree information to improve our understanding of early larval temperature treatment effects on the phenotypic sex. © 2011 Elsevier B.V.

Abozaid H.,Aquaculture and Water Ecology | Wessels S.,Aquaculture and Water Ecology | Horstgen-Schwark G.,Aquaculture and Water Ecology
Sexual Development | Year: 2011

In zebrafish, Danio rerio, a polygenic pattern of sex determination or a female heterogamety with possible influences of environmental factors is assumed. The present study focuses on the effects of an elevated water temperature (35°C) during the embryonic development on sex determination in zebrafish. Eggs derived from 3 golden females were fertilized by the same mitotic gynogenetic male and exposed to a water temperature of 35°C, applied from 5 to 10 h post fertilization (hpf), from 5 to 24 hpf, and from 5 to 48 hpf, which correspond to the following developmental stages: gastrula, gastrula to segmentation, and gastrula to pharyngula stage, respectively. Hatching and survival rates decreased with increasing exposure to high water temperatures. Reductions in the hatching and survival rates were not responsible for differences in sex ratios. Accordingly, exposition of the fertilized eggs to a high temperature (35°C) leads to an increase of the male proportion from 22.0% in the controls to a balanced sex ratio (48.3, 47.5, and 52.6%) in the gastrula, segmentation, and pharyngula groups, respectively. These results prove the possibility to change the pathway of sexual determination during early embryonic stages in zebrafish by exposure to a high water temperature. Copyright © 2011 S. Karger AG, Basel.

Abozaid H.,Aquaculture and Water Ecology | Wessels S.,Aquaculture and Water Ecology | Horstgen-Schwark G.,Aquaculture and Water Ecology
Sexual Development | Year: 2012

Temperature effects on sex determination or differentiation exist in many fish species, with high temperatures predominantly producing more males. The present study aimed at elucidating the genetic background of temperature effects on sex differentiation in zebrafish. Experimental fish were generated by matings between 4 or 6 golden females and a normal or a mitotic gynogenetic male, respectively. All the larvae were reared at 28.5 ° C until they were divided into 3 groups per full-sib family, a control group raised at 28.5 ° C and 2 treatment groups reared at 35 ° C from 20 to 30 dpf or 25 to 35 dpf, respectively. Backcross progenies, reared at 28.5 ° C, were derived from F1 temperature-treated sons (35 ° C, 25-35 dpf) that were sired by a mitotic gynogenetic male and their corresponding mothers. No significant differences were observed regarding the survival rate between the control and treatment groups. Significant differences in the phenotypic male proportions from the controls were observed in groups treated at 35 ° C. The sex ratio in zebrafish was influenced by the male spawner, the female spawner, and a significant interaction of genotype by temperature. Backcross experiments point to a continuum of major genetic, minor genetic, and environmental factors in the expression of the phenotypic sex in zebrafish. Copyright © 2012 S. Karger AG, Basel.

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