Exposure of Larvae to Daily Thermocycles Affects Gonad Development, Sex Ratio, and Sexual Steroids in Solea senegalensis, Kaup

Department of Physiology, Faculty of Biology, University of Murcia Espinardo Campus, Murcia, Spain.
Journal of Experimental Zoology Part A Ecological Genetics and Physiology (Impact Factor: 1.44). 03/2011; 315(3):162-9. DOI: 10.1002/jez.664
Source: PubMed


The effect of water temperature during the development of fish larvae on sex differentiation is well known, but not so well known is the impact of the daily thermocycles. Our aim was to investigate the effect of early exposure of Senegal sole larvae to different temperature cycles on gonad development, sex ratio, and sex steroid (11-ketotestosterone (11-KT); estradiol (E(2) ); and testosterone, (T)) content in muscle extracts of juveniles. From 1 to 97 days posthatching (DPH) fish larvae and post-larvae were subjected to three temperature regimes: Thermophase-Cryophase (TC), Cryophase-Thermophase (CT), and constant temperature. In fish exposed to TC, sex determination occurred earlier, because 90% of soles were males/females at 110 DPH, whereas 45% of fish under CT were undifferentiated at that time. Fish under TC showed the highest growth rates, followed by fish under constant temperature and by fish under CT, the differences being statistically significant between the TC and CT groups. Regarding sex ratio, juveniles exposed to TC showed a higher proportion of females than fish under CT or constant temperature. Under TC, fish showed the highest concentration of E(2) , whereas 11-KT concentration was highest in fish under CT and constant temperature. Fish under constant temperature and CT showed higher T levels than those under TC. These results provide the first insights into the effect of daily thermocycles on sex differentiation in fish, and underline the key role of natural environmental cycles on the control of sex ratios during larval development, which may be applied to the manipulation of sex ratio in aquaculture.

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    • "Recently, we found that rearing at 16 °C during metamorphosis (12–20 dpf) gave 1:1 sex ratios, whereas siblings reared at 20 °C had 62% males (J.P. Cañavate, unpublished observations). Furthermore, in yet another recent study, rearing at 20.7± 0.4 °C resulted in 62% males, whereas different thermocycles resulted in 21–82% males (Blanco-Vives et al., 2011). The presence of balanced sex ratios in fish reared at 16 °C but male-skewed at 20 °C indicates that 20 °C has a slight masculinizing effect. "
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