Meeting Abstract

35.5  Friday, Jan. 4  Time course of changes in plasma hormone concentrations and expression of hormone receptors and osmotic stress transcription factor 1 in the gill of Mozambique tilapia following transfer to a hyperosmotic environment BREVES, J.P.*; FOX, B.K.; PIERCE, A.L.; HIRANO, T.; GRAU, E.G.; Dept. of Molecular Biosciences and Bioengineering & Hawaii Institute of Marine Biology, Univ. of Hawaii breves@hawaii.edu

Mozambique tilapia (Oreochromis mossambicus) possess a remarkable ability to adapt rapidly to changes in environmental salinity and maintain salt and water balance. Changes in environmental salinity modulate blood levels of the pituitary hormones prolactin (PRL) and growth hormone (GH), which act through plasma membrane receptors in the gill and other tissues to restore osmoregulatory homeostasis. We hypothesize that rapid modulation of gene expression of receptors and other osmoregulatory factors in the gill is a critical feature underlying euryhalinity. To test this hypothesis, fresh water (FW)-adapted male tilapia were transferred to 70% seawater (SW) for 24 h, and then to 100% SW for 13 d. Short-term (hours) and long-term (days/weeks) sampling of blood plasma and gill tissue was conducted. Plasma PRL levels were reduced in transferred fish after 3 h and remained low throughout the duration of the experiment, while GH levels were elevated in fish transferred to a hyperosmotic environment at 12 h and 14 d as compared to FW controls. Plasma levels of insulin-like growth factor-I and ghrelin were not affected by the transfer. We report the time course of changes in mRNA levels in the gill that encode osmotic stress transcription factor 1, as well as the PRL, GH and glucocorticoid receptors and the putative somatolactin receptor. This study will elucidate the sequence of events in both the plasma hormone level and gene expression response to an increase in environmental salinity in this teleost fish. Supported by NSF (IOB05-17769) and USDA-CSREES-NRI (2006-35206-16647).