Physiological effects of saline waters on zander.
Using two experiments, the present study assessed the osmoregulatory abilities of zander (Stizostedion lucioperca) [pike perch] in order to determine the chances that further spread of this species in the UK could make use of saltwater bridges. Investigation of the physiological changes accompanying rapid transfer and potential acclimation to 8-35 psu salinities indicated that zander could cope with the lower end of the range at least in the short-term (until 6 days), but could not deal with rapid exposure to 26 or 35 psu. In the estuarine environment, more gradual changes in salinity are likely and may involve tidal cycles. In the second experiment that simulated tidal cycles of rising salinities, short-term exposure to salinities as high as 33 psu did not lead to extremely high plasma osmolalities, though plasma osmolality and chloride concentrations were significantly raised. Zander were stressed by these exposures as evidenced by raised plasma glucose and cortisol. Increased haematocrit appeared to reflect both catecholamine-induced release of erythrocytes and the impact of osmotic water loss in the face of a large osmotic gradient. Adrenergic stress was further indicated by the significant decrease in MCHC. Other physiological parameters revealed that these fish were capable of handling short-term exposure to 29-33 psu, and recovered after return to fresh water. The observed ability for hypoosmoregulation and their capacity to deal with short-term exposure to higher salinities comparable to those experienced during tidal cycles in estuarine and inshore waters suggest that in the United Kingdom, zander located in the lower Ouse and upper Wash may potentially invade new river systems by migration, and that similar migrations may have played a role in the spread of this species through large parts of Europe.