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Effects of Cyclical Changes in Environmental Salinity on Osmoregulatory Parameters in the Mozambique Tilapia

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Title:Effects of Cyclical Changes in Environmental Salinity on Osmoregulatory Parameters in the Mozambique Tilapia
Authors:Pavlosky, Kelsey
Keywords:Mozambique Tilapia
Tidally-Changing Salinity
Date Issued:Dec 2016
Publisher:[Honolulu] : [University of Hawaii at Manoa], [December 2016]
Abstract:Many euryhaline teleost fish, including the Mozambique tilapia, Oreochromis mossambicus, are native to waters in which salinity varies tidally between that of freshwater (FW) and seawater (SW). Acclimation to changes in environmental salinity is regulated largely by the neuroendocrine system, which directs ion extrusion or ion uptake response via the gill and other osmoregulatory tissues. In teleosts, prolactin (PRL) is critical to FW acclimation, stimulating ion uptake mechanisms. Osmoregulation in euryhaline teleosts has been studied extensively in steady state FW and SW, and after one-way transfers between FW and SW. It is unclear, however, how euryhaline fish respond to cyclical salinity changes. Mozambique tilapia were reared in FW, SW, and under a tidal regimen (TR), characterized by salinity changes between FW (TF) and SW (TS) every 6 hours (h), and transferred from FW or SW to TR to investigate adaptive ability to TR. TR fish were also sampled every 3 h in a 24-hour period to observe osmoregulatory parameters throughout the TR cycle. Regardless of the rearing regimen, plasma osmolality changed in direct relation to salinity, rising in SW and falling in FW, while plasma PRL was inversely related to salinity. In fish reared in TR, branchial gene expression of effectors of ion transport and PRL receptors was more similar to those of fish reared in SW than to those in FW. When fish were transferred from either FW or SW to TR, all measured osmoregulatory parameters were identical to those of fish reared in TR by 7 days. In TR fish sampled multiple times over a 24-hour period the greater resolution in sampling revealed several nuances within the overall patterns of salinity and regimen-dependent changes in osmoregulatory parameters. These findings indicate that life-long acclimation to SW and FW does not preclude adaptation to TR at the adult stage. The results also show that throughout a 24-hour period, TR fish are able to compensate for broad and frequent changes in external salinity while maintaining osmoregulatory parameters within a narrow range. These are the first known studies to investigate environmental adaptation of adult Mozambique tilapia to TR, and to characterize osmoregulatory parameters in TR fish over multiple iterations of TF & TS during a full diurnal cycle. As such, these studies have further characterized the effects of TR-acclimation at a more advanced life stage than addressed by previous reports, and have yielded greater insights to rearing in an environment that approximates the native habitat of the Mozambique tilapia.
Description:M.S. University of Hawaii at Manoa 2016.
Includes bibliographical references.
Appears in Collections: M.S. - Molecular Biosciences and Bioengineering

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