Gene and Blood Analysis Reveal That Transfer from Brackish Water to Freshwater Is More Stressful to the Silverside Odontesthes humensis

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.

Evaluation of Reference Genes to Analyze Gene Expression in Silverside Odontesthes humensis Under Different Environmental Conditions

“…Except for atp1a gene, which was previously known (Silveira et al, 2018 ), all the other seven silverside O. humensis candidate RGs analyzed in this study were cloned and partially sequenced for the first time. Furthermore, the new sequences were deposited in the GenBank® (Table 1 ).…”

Modulation of miR-429 during osmotic stress in the silverside Odontesthes humensis

“…Indeed, salinity is a frequent abiotic stressor that restrains fish growth and development by triggering osmotic stress responses. Thus, when fishes are subjected to salinity stress, related genes are activated to induce tolerance to the salinity-mediated stress ( Silveira et al, 2018b ). Although miRNAs provide fish with elaborate strategies for gene regulation at the post-transcriptional level, the precise mechanisms by which miRNAs employ their regulatory function facing osmotic stress are not fully understood.…”

“…Salinity is a frequent abiotic stressor that restricts fish growth and development, and favors the impairment of the existing macromolecules, such as proteins, mRNAs, DNA, and lipids ( Bartel, 2009 ). Thus, when faced with salinity variations, fishes employ many physiological acclimations to rapidly respond to osmotic stress, such as the induction of molecular chaperones, rapid clearance of damaged macromolecules, growth arrest, and the alteration of gene expression of multiple genes that mediates osmotic stress tolerance ( Fiol and Kültz, 2007 ; Richter and Haslbeck, 2010 ; Silveira et al, 2018b ). This gene expression modulation to maintain the osmotic balance may be directly influenced by miRNAs ( Yan et al, 2012a ).…”

Biogeography, habitat transitions and hybridization in a radiation of South American silverside fishes revealed by mitochondrial and genomic RAD data

“…New World silversides (family Atherinopsidae) have repeatedly transitioned between marine and freshwater habitats, but precise knowledge of their phylogenetic history, and therefore the chronology and frequency of inferred habitat transitions, remains contentious (Bloom, Weir, Piller, & Lovejoy, ; Campanella et al, ; Dyer, ). Some freshwater silverside species can osmoregulate in brackish water (Hughes, Somoza, & Nguyen, ; Silveira, Martins, & Domingues, ; Tsuzuki, Aikawá, Strüssmann, & Takashima, ), suggesting that reversals from freshwater to marine habitats may be possible, despite this being a relatively rare phenomenon among ray‐finned fishes (Betancur‐R, Ortí, & Pyron, ). With seven marine and 12 freshwater recognized species (Fricke, Eschmeyer, & van der Laan, ) distributed across coastal marine habitats and in rivers and lakes exclusively in temperate South America (Figure a,b), the atherinopsid genus Odontesthes (locally known as pejerrey in Spanish or peixe‐rei in Portuguese) provides a unique system to study the history and evolutionary consequences of habitat transitions.…”

“…New World silversides (family Atherinopsidae) have repeatedly transitioned between marine and freshwater habitats, but precise knowledge of their phylogenetic history, and therefore the chronology and frequency of inferred habitat transitions, remains contentious (Bloom, Weir, Piller, & Lovejoy, 2013;Campanella et al, 2015;Dyer, 2006). Some freshwater silverside species can osmoregulate in brackish water (Hughes, Somoza, & Nguyen, 2017;Silveira, Martins, & Domingues, 2018;Tsuzuki, Aikawá, Strüssmann, & Takashima, 2000), suggesting that reversals from freshwater to marine habitats may be possible, despite this being a relatively rare phenomenon among ray-finned fishes (Betancur-R, Ortí, & Pyron, 2015).…”