The effects of acute salinity challenges on osmoregulation in Mozambique tilapia reared in a tidally changing salinity

Abstract

This study characterizes the differences in osmoregulatory capacity among Mozambique tilapia, Oreochromis mossambicus, reared in freshwater (FW), in seawater (SW) or under tidally driven changes in salinity. This was addressed through the use of an abrupt exposure to a change in salinity. We measured changes in: (1) plasma osmolality and prolactin (PRL) levels; (2) pituitary expression of prolactin (PRL) and its receptors, PRLR1 and PRLR2; (3) branchial expression of PRLR1, PRLR2, Na− co-transporter (NKCC), α1a and α1b isoforms of Na + /K + -ATPase (NKA), cystic fibrosis transmembrane conductance regulator (CFTR), aquaporin 3 (AQP3) and Na + /H + exchanger 3 (NHE3). Mozambique tilapia reared in a tidal environment successfully adapted to SW while fish reared in FW did not survive a transfer to SW beyond the 6 h sampling. With the exception of CFTR, the change in the expression of ion pumps, transporters and channels was more gradual in fish transferred from tidally changing salinities to SW than in fish transferred from FW to SW. Upon transfer to SW, the increase in CFTR expression was more robust in tidal fish than in FW fish. Tidal and SW fish successfully adapted when transferred to FW. These results suggest that Mozambique tilapia reared in a tidally changing salinity, a condition that more closely represents their natural history, gain an adaptive advantage compared with fish reared in FW when facing a hyperosmotic challenge.

Effect of polychlorinated biphenyls on osmoregulatory response and apoptosis in GIFT tilapia, Oreochromis niloticus

“…When faced with a hyperosmotic challenge, the transcripts of organic osmoregulatory response-related genes (gill nkcc2, atp1a1a, and fxyd7) were found to be induced. This is consistent with the results found in a previous study in which tilapia were transferred from freshwater to seawater (Moorman et al, 2015). Kidney and intestinal nkcc2 transcripts were unchanged in the present study.…”

“…Gene transcriptional levels of ion pumps (such as NKA a3-subunit) have been found to show significant increments in tilapia exposed to various stressors (Seale et al, 2014;Moorman et al, 2015). The key transporter associated with the NaCl transport process is thought to be Na + /K + /2Cl-cotransporter 1 (NKCC2, nkcc2) (Hwang and Lee, 2007).…”

Hormonal regulation of aquaporin 3: opposing actions of prolactin and cortisol in tilapia gill

“…The rapid attenuation of aqp3 by SW, cortisol, and tidally driven changes in salinity suggests that Aqp3 function in the gill is maladaptive to life in SW (Cutler et al 2007, Breves et al 2010a, Moorman et al 2015. Accordingly, we observed that ambient salinity had an 'overriding' effect on whether Prl stimulated aqp3 (Fig.…”

“…We and others have shown that branchial aqp3 expression in teleosts is rapidly modulated in response to changes in salinity, with elevated expression in FW versus SW , Lignot et al 2002, Tse et al 2006, Tipsmark et al 2010, Whitehead et al 2010, Jung et al 2012, Lam et al 2014, Madsen et al 2014, Moorman et al 2015. Prl has long been recognized as "the FW-adapting hormone" in fishes based upon its capacity to support branchial processes essential to life in FW (Hirano 1986, McCormick 2001.…”

“…Multiple teleost Aqps are expressed in osmoregulatory epithelia; for example, Aqp3, an aquaglyceroporin, which transports water, glycerol, and urea, has been studied in a suite of euryhaline teleosts with particular attention to its expression following changes in salinity. In surveyed species, branchial aqp3 gene expression is markedly elevated in FW-versus SW-acclimated animals , Lignot et al 2002, Tse et al 2006, Tipsmark et al 2010, Whitehead et al 2010, Jung et al 2012, Madsen et al 2014, Moorman et al 2015. Although the functional significance of plastic aqp3 expression in the gill stands unresolved, regulated transepithelial water movement, via Aqp3, appears unlikely on the basis that branchial water exchange is disadvantageous for fish in both FW and SW environments (Cerdà & Finn 2010).…”