Some aspects of osmotic and ionic regulation in Adriatic sturgeon Acipenser naccarii. II: Morpho-physiological adjustments to hyperosmotic environments

Abstract

A salt water exposure trial with juvenile Adriatic sturgeon, Acipenser naccarii, ( 5 months old; mean (* SD) weight = 56f28 g) was initiated by direct transfer from freshwater (FW) to brackish water (BW) of medium (310 mOsm.Kg-' = 11 %) or high salinity (640 mOsm.Kg-' = 23 960). Survival at 6 weeks and homeostatic regulation of plasma osmolality and ion concentrations demonstrated that A. naccarii of this age and/or size class possess the ability to adapt to hyperosmotic environments. Regulation of the osmotic status of body fluids was associated with differences in the number of mitochondriarich (MR) cells on the gill lamellae, whereby sturgeon in high salinities exhibited reduced MR cell numbers as compared with those in FW. Measurement of Na+,K+-ATPase activity in crude gill homogenates from the three groups of sturgeon revealed higher activity in sturgeon at salinities of 3 10 and 640 mOsm.Kgrelative to those in FW; significantly higher in the sturgeon at 640 mOsm.Kg-I. There were no differences in H+-ATPase activity amongst the groups, as measured on the same crude homogenates, but there was a significant increase in the ratio of Na+,K'-ATPase to H'-ATPase in the sturgeon in water at 640 mOsm.Kg-' relative to those in FW. There was a significant negative linear correlation between gill MR cell number and Na+,K+-ATPase activity. Apparently successful adaptation to BW was also indicated by similar low levels of serum cortisol, and similar rates of resting oxygen consumption, in all groups. Nonetheless, a growth study on triplicate groups of 40 tagged sturgeon in FW or BW at 600 mOsm.Kg-I (20 %) revealed that animals in BW grew less well and exhibited less efficient feed conversion. The results indicate that although sturgeon exhibit some morpho-physiological adjustments to hyperosmotic environments and are able thereby to regulate plasma ions and osmolality in BW at 310 and 640 mOsm.Kg-', they do not grow as well in BW at 600 mOsm.Kg-' as they do in FW and, in fact, died when disturbed by heavy activity near the tanks.

Comparative analysis of branchial ionocytes in Caspian Sea zander, Sander lucioperca (Linnaeus, 1758) using Na+, K+-ATPase immunolocalisation at different salinities

“…In some other studies also, the gill NKA activity followed this pattern, as the lowest NKA activity levels were obtained in brackishwater conditions (Laiz-Carrion et al, 2005;Kang et al, 2008;Kang et al, 2012;Khodabandeh et al, 2009a). Since NKA is highly expressed in fish gill ionocytes, its activity at the gill level is expected to be reduced with decreased ionocyte size and number (Evans, 1993;Cataldi et al, 1995;McCormick, 1996;McKenzie et al, 1999;Mancera and McCormick, 2000). Low values of the ionocyte size, number and the gill NKA activity reported previously in the literature for fish acclimated to brackishwater has been confirmed in the current study, especially for 1g fingerlings, by a reduction in the number and size of ionocytes under similar conditions.…”

Osmoregulation in juvenile Chinese sturgeon (Acipenser sinensis Gray) during brackish water adaptation

“…naccarii, Cataldi et al 1995bA. naccarii, Cataldi et al , 1999McKenzie et al 1999;Martínez-Á lvarez et al 2002). These changes can be attributed to changes in the water content in the blood, caused by the change in environmental salinity (Plaut 1998).…”

Age/size effects on juvenile green sturgeon, Acipenser medirostris, oxygen consumption, growth, and osmoregulation in saline environments

“…Juveniles have higher osmolality and plasma ion levels than adults of the same species in the same salinities Cech 1985, 1987 ; Table 4). Presumably, because sturgeons hatch and grow at least initially in FW, they regulate at elevated ion homeostasis levels in hyperosmotic salinities, as compared to hyposmotic salinities Cech 1985, 1987;Altinok et al 1998;Krayushkina 1998;McKenzie et al 1999;Rodriguez et al 2002). Some juveniles also appear to regulate at nearly isosmotic levels, when salinities are approximately 8-12& (Natochin et al 1985;Shelukhin et al 1990).…”

“…Most recent studies on the aerobic metabolic costs of salinity in teleosts have not found large costs (Boeuf and Payan 2001), except when salinities are changing rapidly (Morgan et al 1997). Although some aerobic metabolic studies have been conducted on sturgeon juveniles at different salinities (Shelukhin et al 1990;Secor and Gunderson 1998;McKenzie et al 1999McKenzie et al , 2001a, there have been no studies investigating size or age effects on salinity-associated metabolic costs. Metabolism measurements, as physiological tools, can be used to make predictions about organisms' optimal environmental conditions (Cech 1990).…”