Physiological effects of saline waters on zander

Abstract

Rapid transfer of zander Stizostedion lucioperca to hypoosmotic brackish water (mean osmolality 230 mOsmol kg 1 , c. 8 psu) significantly increased plasma chloride concentrations after 24 h compared to those transferred to fresh water, although plasma osmolality was not significantly affected. After 6 days, plasma osmolality was slightly elevated but stable plasma glucose and cortisol concentrations and blood haematocrit and haemoglobin suggest a lack of hormonal stress responses and resultant secondary effects. Rapid transfer of zander to a more saline environment, hyperosmotic to plasma (mean osmolality 462 mOsmol kg 1 , c. 16 psu) induced a greater increase in plasma osmolality and chloride concentrations within 24 h, with a further rise after 6 days exposure, but all fish maintained a state of hypo-osmoregulation both 24 h and 6 days after transfer. The initial osmotic disturbance (at 24 h) was accompanied by increased plasma glucose, blood haematocrit and haemoglobin and a decreased mean cell haemoglobin concentration (MCHC), suggesting an adrenergic stress response, but these parameters fully recovered within 6 days of exposure to this hyperosmotic environment with MCHC rising to exceed the level in freshwater fish. Zander did not survive rapid transfer to more hyperosmotic conditions (750 or 1001 mOsmol kg 1 , 26-35 psu), but they did survive exposure to simulated ' tidal cycles ' of rising and declining salinity, peaking after 6 h at c. 29 or 33 psu. Although osmotic disturbance was apparent after 6 h exposure and other physiological parameters suggested both adrenergic and corticosteroid components of a stress response, rapid recovery was apparent after return to fresh water. The results indicate that the zander, a non-indigenous species in the U.K., has a high level of osmotic tolerance and a degree of hypo-osmoregulation in saline environments not found in most stenohaline freshwater teleosts. This osmoregulatory ability could enable invasion of new U.K. river systems by using inshore marine environments of low salinity as saltwater bridges. 2001 The Fisheries Society of the British Isles

Metabolic substrates are not mobilized from the osmoregulatory organs (gills and kidney) of the estuarine pufferfishes Sphoeroides greeleyi and S. testudineus upon short-term salinity reduction

“…Despite of the changes in hematocrit seen in the pufferfishes, their muscle cells apparently have a greater or faster capacity for tissue water regulation (as also in Prodocimo & Freire, 2006), as in both species no differences in muscle tissue water content were noted, compatible with a previous report on the red grouper Epinephelus akaara and the black sea bream Mylio macrocephalus also submitted to dilute seawater (Woo & Wu, 1982). The values of muscle water content (~ 80%) for both pufferfishes were similar to previous values reported for other euryhaline species (Feldmeth & Waggoner, 1972;Plaut, 1998;Claireaux & Audet, 2000;Brown et al, 2001;Martinez-Álvarez et al, 2002), as well as for the same species (Prodocimo & Freire, 2006). No mobilization of the metabolic substrates stored in the gills or kidney or in plasma glucose have been detected in S. testudineus and S. greeleyi upon this short-term exposure to salinity reduction.…”

“…Hematocrit and muscle tissue water are simple and useful techniques frequently employed to access osmotic challenges to the intracellular compartment (Plaut, 1998;Marshall et al, 1999;Claireaux & Audet, 2000;Brown et al, 2001;Martinez-Álvarez et al, 2002;Prodocimo & Freire, 2006). Hematocrit results obtained for S. testudineus and S. greeleyi were similar to those reported for other teleosts, of ~25-30% (Plaut, 1998;Claireaux & Audet, 2000;Brown et al, 2001;Martinez-Álvarez et al, 2002). Salinity reduction (5‰) lead to increased hematocrit in both pufferfishes, a result which may reflect red cell swelling, and the results in the S. greeleyi were higher than those of S. testudineus.…”

“…In this case, loss of extracellular water to the external medium would be the primary cause, although partially compensated by red cell shrinkage. However, eventually, regulatory volume increase of the red cells, coupled to an increase in red cell counts (long-term change) in order to cope with increasing demand for oxygen delivery following the increased metabolism would at the end lead to increased hematocrit (Plaut, 1998;Claireaux & Audet, 2000;Brown et al, 2001;Martinez-Álvarez et al, 2002). In fact, in either direction, the response is variable, depending on the time of exposure, magnitude of the salinity challenge imposed, degree of change in plasma osmolality, and volume regulatory capacity of the red blood cells.…”

Physiological responses to acute temperature increase in European eels Anguilla anguilla infected with Anguillicola crassus

“…Plasma samples were kept at -20°C until required. Plasma glucose concentrations were determined spectrophotometrically (Boehringer Mannheim; kit MPR3) and plasma cortisol concentrations measured by radioimmunoassay (RIA) (Brown et al 2001, Gollock et al 2004.…”

Baseline survey of the fish fauna of a highly eutrophic estuary and evidence for its colonisation by Goldfish (Carassius auratus)

“…1). It is relevant that such movements have been recorded in other freshwater fish species, such as Zander Stizostedion lucioperca, that have previously been considered stenohaline (Brown et al 2001;.…”