Acclimation of brackish water pearl spot (Etroplus suratensis) to various salinities: relative changes in abundance of branchial Na+/K+-ATPase and Na+/K+/2Cl− co-transporter in relation to osmoregulatory parameters

Abstract

The present study was conducted to elucidate the osmoregulatory ability of the fish pearl spot (Etroplus suratensis) to know the scope of this species for aquaculture under various salinities. Juvenile pearl spot were divided into three groups and acclimated to freshwater (FW), brackish water (BW) or seawater (SW) for 15 days. The fish exhibited effective salinity tolerance under osmotic challenges. Although the plasma osmolality and Na(+), K(+) and Cl(-) levels increased with the increasing salinities, the parameters remained within the physiological range. The muscle water contents were constant among FW-, BW- and SW-acclimated fish. Two Na+/K+-ATPase α-isoforms (NKA α) were expressed in gills during acclimation in FW, BW and SW. Abundance of one isoform was up-regulated in response to seawater acclimation, suggesting its role in ion secretion similar to NKA α1b, while expression of another isoform was simultaneously up-regulated in response to both FW and SW acclimation, suggesting the presence of isoforms switching phenomenon during acclimation to different salinities. Nevertheless, NKA enzyme activities in the gills of the SW and FW individuals were higher (p < 0.05) than in BW counterparts. Immunohistochemistry revealed that Na(+)/K(+)-ATPase immunoreactive (NKA-IR) cells were mainly distributed in the interlamellar region of the gill filaments in FW groups and in the apical portion of the filaments in BW and SW groups. The number of NKA-IR cells in the gills of the FW-acclimated fish was almost similar to that of SW individuals, which exceeded that of the BW individuals. The NKA-IR cells of BW and SW were bigger in size than their FW counterparts. Besides, the relative abundance of branchial Na(+)/K(+)/2Cl(-) co-transporter showed stronger evidence in favor of involvement of this protein in hypo-osmoregulation, requiring ion secretion by the chloride cells. To the best of our knowledge, this is the first study reporting the wide salinity tolerance of E. suratensis involving differential activation of ion transporters and thereby suggesting its potential as candidate for fish farming under different external salinities.

Deviation of habitat salinity during seasonal gonad recrudescence affects plasma sex steroid levels and suppresses gonadal maturation in an euryhaline fishEtroplus suratensis

“…We found that pearlspot maintained the plasma osmolality between 307.83 mM and 355.5 mM during active reproductive phase under hypo‐ and hyper‐osmoregulation, respectively, which is similar to the ranges of osmolality reported by Chandrasekar et al. () in case of immature pearlspot. Plasma osmolality is considered as a key indicator for monitoring osmoregulatory ability of fish (Evans et al., ) which remains in the range of 285–320 mOsm kg −1 in most of the euryhaline teleost fish (Kang, Tsai, Lee & Hwang, ).…”

“…It can therefore be concluded that initial increase in cortisol levels in Etroplus suratensis under salinity changes may be attributed to pre‐acclimation stress, which decreased afterwards in all the groups suggesting acclimation under various salinities. However, compared to other groups, elevated levels in SW group may be attributed to hypo‐osmoregulatory adaptation under the control of cortisol, which is known to be responsible for cellular differentiation of chloride cells for enhancing branchial Na⁺/K⁺‐ATPase activity reported in SW‐acclimated pearlspot and other teleosts (Chandrasekar et al., ; McCormick, ). This, being an energy expensing event, may lead to low leftover energy for other metabolic actions.…”

“…FCE was found largely affected in SW treatment group which is in agreement with findings of Imsland et al., ; elucidated improved FCE in Atlantic halibut ( Gadus morhua ) cultured in intermediate salinities (15–20 ppt). Transient changes in gill chloride cell dynamics including sodium—potassium pump (Na + ‐K + ‐ATPase) and Na + /K + /2Cl − co‐transporter (NKCC) activities play a key role in the ion regulation process after SW or FW exposure in this species (Chandrasekar et al., ). Specific estimates of this osmoregulatory cost (based on salinity‐related differences in metabolism) in Oreochromis niloticus is 19% and 29% of the total body metabolism in FW and SW respectively (Farmer & Beamish, ), whereas Morgan, Sakamoto, Grau and Iwama () recorded it as 20% in case of SW acclimation.…”

“…(Evans, Piermarini & Choe, 2005). Chandrasekar et al (2014) found that pearlspot, alike other euryhaline teleost fish (Oryzias dancena, Plactichthys flesus, Oreochromis mossambicus, Poecilla reticulate, Oryza latipes and Dicentrarchus labrax etc. ), has an efficient capacity of acclimation of osmoregulatory function in different salinities.…”

Effects of salinity acclimation and eyestalk ablation on Na+, K+, 2Cl− cotransporter gene expression in the gill of Portunus trituberculatus:a molecular correlate for salt-tolerant trait

“…NKCC is an integral membrane protein responsible for the simultaneous transport of one Na + , one K + , and two Cl − ions from the external to the internal side of epithelial cells (Kang et al 2010). Although previous studies suggest that NKCC plays a critical role in the osmoregulatory endurance of fish (Kang et al 2010;Watson et al 2014;LorinNebel et al 2006;Ip et al 2013;Chandrasekar et al 2014), its role in salinity adaptations has been little studied in crustaceans compared to other ion transport genes (i.e., Na + , K + -ATPase, V-type H + -ATPase, carbonic anhydrase (CA)) (Tsai and Lin 2007;Lucu et al 2008;Firmino et al 2011;Han et al 2015).…”