Osmoregulatory mechanisms in juveniles of Paralichthys orbignyanus sole submitted to hyposmotic shock
Changes over 72 h in different osmoregulatory parameters of Paralichthys orbignyanus sole submitted to hyposmotic shock were evaluated. A total of 132 juveniles of sole were distributed in 22 tanks, adjusted according to the salinity appropriate to the experimental treatment (30 ‰ for control and 0 ‰ for osmotic shock). For biochemical and histological analyzes, blood, gills, kidney and brain samples were collected at times 0, 2, 6, 12, 24 and 72 h. A rapid reduction in osmolality and Na +, Cl-, Ca2 + and Mg2 + ions can be observed immediately after the hyposmotic shock, without restoring its initial levels until the end of the experiment. The density of chloride cells was not altered by the treatment. However,the glomerular area showed a significant increase after two hours of osmotic shock, showing the role of the kidney in increasing the glomerular filtration rate to compensate for osmotic influx of water. A relationship between cortisol and osmo and ionoregulation cannot be verified. Carbonic anhydrase (CA) demonstrated an increase of up to two times in its activity, for the osmotic shock group, demonstrating its relationship with the Na +/H + and Cl-/HCO3 exchangers. Also, the branchial and cerebral N + K +/ATPases (NKA) showed an increase in their activities after osmotic shock, demonstrating their positive response in hyposmotic media. During the initial 72 h, the main osmoregulatory mechanisms are the increase in the renal glomerular area and increased activity of the AC and NKA gill and brain enzymes.