Meeting Abstract
We examined ionoregulation when Amargosa pupfish (Cyprinodon nevadensis amargosae) acclimated to brackish water (7.5 ppt) experienced a shift to fresh water (0.3 ppt), seawater (35 ppt), or hypersaline (55 ppt) conditions. Fish transferred to 35 ppt or 55 ppt exhibited elevated plasma osmolality and Cl– levels by 8 h, which gradually recovered to baseline levels within 14 days. This recovery of plasma ionic status corresponded to an increase in Na+/K+-ATPase activity and elevation in relative mRNA levels for several gill Na+ and Cl– transport proteins including cystic fibrosis transmembrane conductance regulator, Na+/K+/2Cl– cotransporter-1, and Na+/HCO3– cotransporter-1. Osmotic transcription factor-1 (ostf-1) transcript abundance also exhibited a brief elevation in fish transferred to 55 ppt, suggesting that ostf-1 may mediate transcriptional responses to elevated salinities. In contrast, pupfish transferred from 7.5 ppt conditions to 0.3 ppt exhibited a decline in plasma osmolality and elevations in relative mRNAs encoding Na+/H+ exchanger isoform-2 and V-type H+-ATPase in the gills within 8 h, which was subsequently followed by increased mRNA levels for Na+/H+ exchanger isoform-3, carbonic anhydrase-2, and aquaporin-3 within 24 h of salinity transfer. A gradual increase (by 14 days) in relative mRNA levels for a Na+/Cl– cotransporter was also observed in fish shifted to 0.3 ppt. These results confirm the high euryhalinity of this species and elucidate the mechanisms by which the gill epithelium of euryhaline desert pupfishes maintains ionic and osmotic balance under rapidly shifting salinity conditions.
