Level of serum cortisol and Na⁺/K⁺ATP-ase activity of gills and kidneys in different acipenserids

Abstract

The levels of cortisol in blood serum and the Na + /K + activated ATP-ase activity in the homogenates of the gills and the kidneys were measured in different species of acipenserids in freshwater (control) and after different periods of acclimation to brackish water of 12.5-12.7‰ salinity. Immature sturgeons (2+ years old) were used for the study: the sterlet Acipenser ruthenus L.-a freshwater species from the middle of the Volga River; the Siberian sturgeon from the Lena River A. baerii Brandt -a freshwater species that performs short migrations to brackish waters (5-10‰) of estuaries for feeding; the Russian sturgeon A. gueldenstaedtii Brandt and the starred sturgeon A. stellatus Pallas -both are diadromous species of the Volga-Caspian basin that have regular migrations to brackish water (up to 14‰). The starred sturgeon was additionally held in 18‰ after 12.7‰. The investigated species from freshwater have similar levels of serum cortisol, but different dynamics of this hormone during exposure in brackish water. After seven days of the experiment, the level of serum cortisol increased (p<0.01) 4.1 times in the sterlet and 3 times in the Siberian sturgeon. In the Russian sturgeon, after 7 days of exposure, cortisol level was similar to levels of control fish, although after 3 and 12 hours of acclimation (in the transition period to hypo-osmotic regulation) the hormone levels decreased (p<0.05). In the starred sturgeon, cortisol levels remained without changes during all periods of its life in brackish water. There was the increase of gill Na + /K + -activated ATP-ase activity only in the starred sturgeon exposed in water of 12.7‰ and 18‰ salinity. During acclimation to brackish water of 12.5-12.7‰ salinity, the enzyme activity did not change in the Siberian and the Russian sturgeons and decreased in the starlet. Levels of kidney Na + /K + -activated ATP-ase activity at this period decreased in studied species excluding the Siberian sturgeon that kept the enzyme activity without the changes. The conclusion derived from these studies was that the changes in the serum cortisol levels and Na + /K + ATP-ase activities in gills and kidneys (after fish being transferred to brackish water) explain to a great extent the osmotic and ionic regulatory capacities in different acipenserid species.

Morphofunctional remodelling of the osmoregulatory system in starred sturgeon Acipenser stellatus (Acipenseridae) during transition from hyperosmotic to hypoosmotic regulation

“…In the earlier studies, we (Krayushkina et al, 2006) have observed a significant increase in blood cortisol under acclimation to a hyperosmotic environment (salinity 12.5‰) in a less euryhaline sturgeon spe cies-freshwater sterlet A. ruthenus, which acclimates to such environment as an osmoconformer, and Sibe rian sturgeon of the Lena River population A. baerii, which has a limited osmoregulatory capacity. Under these conditions, the cortisol concentration increases 4 fold in sterlet and 3 fold-in the Siberian sturgeon, as compared with the hormone level in fish from fresh water.…”

“…The euryhaline species of acipenserids (Acipens eridae) that perform regular migrations "river → sea → river" are capable of maintaining a relatively constant serum osmolality when the environmental salinity is changed (Krayushkina et al, 1973;Krayushkina, Moiseenko, 1977;Krayushkina, 1998Krayushkina, , 2006Krayush kina, Semenova 2006). In these sturgeon species, as well as in the euryhaline teleosts (Zaks and Sokolova, 1965;Krayushkina 1983;Krayushkina et al, 1995), hyperosmotic regulation changes to the hypoosmotic during their transition from the river into the sea and thus a relative stability of blood serum osmolarity in the new environment is maintained.…”

Salinity effects on osmoregulation and gill morphology in juvenile Persian sturgeon (Acipenser persicus)

“…Since NKA is highly expressed in fish chloride cells, its activity at the gill level must be enhanced with increased chloride cell size and number. This occurs in teleosts (Evans 1993;Cataldi et al 1995;McCormick 1996;McKenzie et al 1999;Mancera and McCormick 2000) and in sturgeons such as the starred sturgeon, A. stellatus, and the green sturgeons, A. medirostris, where NKA activity increases due to FW to BW transfer (Krayushkina et al 2006;Allen et al 2009). For Persian sturgeon juveniles, chloride cell hyperplasia appears to be salinity dependent with a 1.3-fold increase in the number of chloride cells within 10 days of abrupt or gradual transfer to BW.…”

“…In some species and notably salmonids, NKA activity increases during transfer from FW to hyperosmotic condition and is directly correlated to the increased functional activity of branchial chloride cells (Marshall and Bryson 1998;Krayushkina et al 2006). Despite similar response in some sturgeons, changes of NKA activity with salinity are species specific and may also change through development (age or body size) in sturgeons Rodriguez et al 2002;Martinez Alvarez et al 2005;Krayushkina et al 2006).…”

“…This is consistent with previous work on other sturgeon species. Late juvenile or adult sturgeons such as the Russian sturgeon, A. gueldenstaedtii, the starred sturgeon, A. stellatus and the beluga, Huso huso, have the ability to quickly adapt their physiology when transferred from FW to 12-18 % BW, but younger stages such as larvae and 'fingerlings' (or fry) cannot tolerate increased salinity (Krayushkina et al 2006). Also, 4, 12, 36 and 150 days post-hatching/dph Adriatic sturgeon, A. naccarii, die within the first 24 h of abrupt exposure to 23 % BW .…”