Abstract
Silversides are fish that inhabit marine coastal waters, coastal lagoons, and estuarine regions in southern South America. The freshwater (FW) silversides have the ability to tolerate salinity variations. Odontesthes humensis have similar habitats and biological characteristics of congeneric O. bonariensis, the most studied silverside species and with great economic importance. Studies revealed that O. bonariensis is not fully adapted to FW, despite inhabiting hyposmotic environments in nature. However, there is little information about stressful environments for cultivation of silverside O. humensis. Thus, the aim of this study was to evaluate the stress and osmoregulation responses triggered by the osmotic transfers on silverside O. humensis. Silversides were acclimated to FW (0 ppt) and to brackish water (BW, 10 ppt) and then they were exposed to opposite salinity treatment. Silverside gills and blood were sampled on pre-transfer (D0) and 1, 7, and 15 days (D1, D7, and D15) after changes in environmental salinity, the expression levels of genes atp1a3a, slc12a2b, kcnh1, and hspa1a were determined by quantitative reverse transcription-PCR for evaluation of osmoregulatory and stress responses. Furthermore, glycemia, hematocrit, and osmolality were also evaluated. The expression of atp1a3a was up- and down-regulated at D1 after the FW–BW and BW–FW transfers, respectively. Slc12a2b was up-regulated after FW–BW transfer. Similarly, kcnh1 and hspa1a were up-regulated at D1 after the BW–FW transfer. O. humensis blood osmolality decreased after the exposure to FW. It remained stable after exposure to BW, indicating an efficient hyposmoregulation. The glycemia had a peak at D1 after BW–FW transfer. No changes were observed in hematocrit. The return to the pre-transfer levels at D7 after the significant increases in responses of almost all evaluated molecular and blood parameters indicated that this period is enough for acclimation to the experimental conditions. In conclusion, our results suggest that BW–FW transfer is more stressful to O. humensis than FW–BW transfer and the physiology of O. humensis is only partially adapted to FW.
Highlights
Odontesthes spp., popularly known as pejerreyes or silversides, is a fish genus naturally endemic from South America waters (Bemvenuti, 2006)
When fishes are subjected to salinity stress, related genes are activated to induce salinity stress tolerance
This study was successful in the identification and characterization of atp1a3a, slc12a2b, kcnh1, and hspa1a mRNA sequences in the silverside O. humensis
Summary
Odontesthes spp., popularly known as pejerreyes or silversides, is a fish genus naturally endemic from South America waters (Bemvenuti, 2006). This genus comprises the biggest number of species of Atherinopsidae and the broader area of distribution, with species inhabiting marine coastal waters, coastal lagoons, and estuarine regions in southern South America (Dyer, 2006). In Japan, O. bonariensis cultivation has been deployed, due to the efforts to farming conditions improvements in the last few years (Tsuzuki et al, 2000b, 2001, 2007) This species has been introduced in Chile, Bolivia, and Italy (Dyer, 2000, 2006). The species is exotic and has economic importance in Peru, where O. bonariensis was introduced in the Titicaca Lake in 1946 and until nowadays continues to be caught (Loubens and Osorio, 1991)
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