Physiological and Respiratory Responses of the Mozambique Tilapia (Oreochromis mossambicus) to Salinity Acclimation

We examined the effects of environmental salinity on circulating levels of the two prolactins (tPRL 177 and tPRL 188 ) and levels of pituitary tPRL 177 and tPRL 188 mRNA in the euryhaline tilapia, Oreochromis mossambicus. Fish were sham-operated or hypophysectomized and the rostral pars distalis (RPD) autotransplanted onto the optic nerve. Following post-operative recovery in ¼ seawater, tilapia were transferred to fresh water (FW), ¼ seawater (SW) or SW. Serum tPRL 177 and tPRL 188 levels in sham-operated and RPD-autotransplanted fish were highest in FW and decreased as salinity was increased. tPRL 177 and tPRL 188 mRNA levels in RPD implants as well as in pituitaries from the sham-operated fish were also highest in FW and decreased with increasing salinity. Serum osmolality increased with salinity, with the highest levels occurring in the seawater groups. We conclude that some plasma factor (probably plasma osmolality), in the absence of hypothalamic innervation, exerts a direct regulatory action on prolactin release and gene expression in the pituitary of O. mossambicus. This regulation is in accord with the actions of the two prolactins in the freshwater osmoregulation of the tilapia.

Section: Discussionsupporting

confidence: 92%

Is the primitive regulation of pituitary prolactin (tPRL177 and tPRL188) secretion and gene expression in the euryhaline tilapia (Oreochromis mossambicus) hypothalamic or environmental?

Shepherd¹,

Sakamoto

Hyodo³

et al. 1999

“…Euryhaline species have the remarkable ability to acutely withstand wide fluctuations in environmental salinity. During acute seawater (SW) acclimation, these animals overcome an increase in plasma osmolality of as much as 175 mOsm through active excretion of ions, consuming 20-68% of their total metabolic energy demand (Morgan et al 1997, Boeuf & Payan 2001. The primary site of ion exchange is the gill (Evans et al 2005), which has a low capacity for the oxidation of fatty acids or ketones (Segner et al 1997, Crockett et al 1999.…”

Section: Introductionmentioning

confidence: 99%

Role for leptin in promoting glucose mobilization during acute hyperosmotic stress in teleost fishes

Baltzegar

Reading

Douros

et al. 2013

Osmoregulation is critical for survival in all vertebrates, yet the endocrine regulation of this metabolically expensive process is not fully understood. Specifically, the function of leptin in the regulation of energy expenditure in fishes, and among ectotherms, in general, remains unresolved. In this study, we examined the effects of acute salinity transfer (72 h) and the effects of leptin and cortisol on plasma metabolites and hepatic energy reserves in the euryhaline fish, the tilapia (Oreochromis mossambicus). Transfer to 2/3 seawater (23 ppt) significantly increased plasma glucose, amino acid, and lactate levels relative to those in the control fish. Plasma glucose levels were positively correlated with amino acid levels (R 2 Z0.614), but not with lactate levels. The mRNA expression of liver leptin A (lepa), leptin receptor (lepr), and hormone-sensitive and lipoprotein lipases (hsl and lpl) as well as triglyceride content increased during salinity transfer, but plasma free fatty acid and triglyceride levels remained unchanged. Both leptin and cortisol significantly increased plasma glucose levels in vivo, but only leptin decreased liver glycogen levels. Leptin decreased the expression of liver hsl and lpl mRNAs, whereas cortisol significantly increased the expression of these lipases. These findings suggest that hepatic glucose mobilization into the blood following an acute salinity challenge involves both glycogenolysis, induced by leptin, and subsequent gluconeogenesis of free amino acids. This is the first study to report that teleost leptin A has actions that are functionally distinct from those described in mammals acting as a potent hyperglycemic factor during osmotic stress, possibly in synergism with cortisol. These results suggest that the function of leptin may have diverged during the evolution of vertebrates, possibly reflecting differences in metabolic regulation between poikilotherms and homeotherms.

“…Both species are highly euryhaline; however, their acclimation 'strategy' in molecular terms seems different when exposed to increasing salinity. The Mozambique tilapia develops the appropriate hypo-osmoregulatory mechanisms gradually when stimulated by increased salinity (Morgan et al 1997, Uchida et al 2000. Thus, the energy to build the appropriate mechanisms is only spent when needed.…”

Section: Introductionmentioning

confidence: 99%

Differential effects of cortisol and 11-deoxycorticosterone on ion transport protein mRNA levels in gills of two euryhaline teleosts, Mozambique tilapia (Oreochromis mossambicus) and striped bass (Morone saxatilis)

Kiilerich¹,

Tipsmark²,

Borski³

et al. 2011

The role of cortisol as the only corticosteroid in fish osmoregulation has recently been challenged with the discovery of a mineralocorticoid-like hormone, 11-deoxycorticosterone (DOC), and necessitates new studies of the endocrinology of osmoregulation in fish. Using an in vitro gill explant incubation approach, DOC-mediated regulation of selected osmoregulatory target genes in the gill was investigated and compared with that of cortisol in two euryhaline teleosts, Mozambique tilapia (Oreochromis mossambicus) and striped bass (Morone saxatilis). The effects were tested in gills from both fresh water (FW)-and seawater (SW)-acclimated fish. Both cortisol and DOC caused an up-regulation of the Na C ,K C -ATPase a1 subunit in SW-acclimated tilapia but had no effect in FW-acclimated fish. Cortisol conferred an increase in NaK cotransporter (NKCC) isoform 1a transcript levels in FW-and SW-acclimated tilapia, whereas DOC had a stimulatory effect only in SW-acclimated fish. Cortisol had no effect on NKCC isoform 1b mRNA levels at both salinities, while DOC stimulated this isoform in SW-acclimated fish. In striped bass, cortisol conferred an up-regulation of Na C ,K C -ATPase a1 and NKCC transcript levels in FW-and SW-acclimated fish, whereas DOC resulted in down-regulation of these transcripts in FW-acclimated fish. It was also found that both corticosteroids may rapidly (30 min) alter the mitogen-activated protein kinase signalling pathway in gill, inducing phosphorylation of extracellular signalregulated kinase 1 (ERK1) and ERK2 in a salinity-dependent manner. The study shows a disparate organisation of corticosteroid signalling mechanisms involved in ion regulation in the two species and adds new evidence to a role of DOC as a mineralocorticoid hormone in teleosts.