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Also, the branchial hsp70 levels in fish following chronic salinity acclimation and abrupt hypo-osmotic exposure to 6 ppt were assessed by Western blotting. Upon chronic salinity acclimation, the lowest branchial hsp70 level was found in fish cultured in an iso-osmotic salinity of 12 ppt and the highest was in 50 ppt and 6 ppt environments. Freshwater acclimation resulted in return to lower hsp70 level. The results indicated that iso-osmotic salinity would bring about the least stress level while 50 ppt and 6 ppt were the most stressful salinities to Sparus sarba as indicated by using hsp70 expression as a biomarker of stress. Compared to 50 ppt and 6 ppt, the stress level of fish in fresh water was lower. On the other hand, Sparus sarba exhibited a significant increase in branchial hsp70 level immediately after abrupt hypo-osmotic exposure to 6 ppt when compared with seawater fish sampled at the same time point and increased hsp70 level was sustained throughout the sampling period, indicating the exposure was stressful to the fish.In the present study, pituitary and serum levels of prolactin in a marine teleost, Sparus sarba, chronically acclimated to various salinities: fresh water (0 ppt), hypo-osmotic (6 ppt), iso-osmotic (12 ppt), normal seawater (33 ppt) and hypersaline (50 ppt) or abruptly exposed to a hypo-osmotic environment of 6 ppt were quantified by the developed peptide-based indirect ELISAs. Progressive increases in pituitary and serum prolactin were found as chronic salinity acclimation progressed from seawater to fresh water. Also, prolactin secretion was immediately induced by abrupt hypo-osmotic exposure to 6 ppt and remained significantly elevated up to 5 days post-exposure to 6 ppt. The results underline the importance of prolactin in marine teleosts kept in fresh water or waters of low salinity. However, there was no significant difference in pituitary prolactin during the course of the abrupt hypo-osmotic exposure experiment. The results may indicate that prolactin might be secreted rapidly from pituitary in large quantities to cope with abrupt exposure to a low-salinity environment.In the present study, the effects of pharmacological drugs on prolactin levels in pituitary and serum of Sparus sarba were investigated. An increase in prolactin synthesis and release but a decrease in branchial hsp70 expression were found after treatment with sulpiride, a DA-D2 receptor antagonist. In contrast, a reduction in prolactin levels in pituitary and serum but an elevation in hsp70 level in gill were observed following administration of bromocriptine, a DA-D2 receptor agonist. Since hsp70 expression indicates the stress levels, the results of these studies supported the notion that increased prolactin synthesis and release might be related to a reduced stress state and prolactin might have a protective effect on stress tolerance in fish.Lastly, the role of prolactin in regulating apoptosis in Sparus sarba branchial cells was examined. Successful induction of apoptosis was indicated by an increase in the apoptotic parameter caspase-3 activity in primary cultures of Sparus sarba branchial cells treated with camptothecin, a specific inducer of apoptosis. In this study, prolactin was shown to be anti-apoptotic in Sparus sarba branchial cells as co-treatment with ovine prolactin (oPRL) and camptothecin has been observed to attenuate the elevated caspase-3 activity in gill cell primary cultures. Also, prolactin was found to protect the branchial cells from apoptosis by maintaining the hsp70 level in the cells treated with camptothecin.The objectives of the present study were to investigate the roles of prolactin in salinity adaptation, hsp70 expression and apoptosis in silver sea bream (Spaurs sarba). Firstly, specific peptide-based indirect ELISAs were developed for pituitary and serum prolactin of Sparus sarba. These assays had been validated by parallelism between the dilution response curves using serially diluted pituitary homogenate and serum sample with the standard curves of the synthetic peptide derived from the amino acid sequence of black sea bream (Acanthopagrus schlegelii ) prolactin.Ng, Ho Yuen Andus."September 2007."Adviser: N. Y. S. Woo.Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4567.Thesis (Ph.D.)--Chinese University of Hong Kong, 2007.Includes bibliographical references (p. 143-189).Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Abstracts in English and Chinese.School code: 1307