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Identifier 000391332
Title Μolecular and endocrine regulation of the stress response during early developmental stages in European sea bass (Dicentrarchus labrax)
Alternative Title Μοριακή και ενδοκρινική ρύθμιση της απόκρισης στην καταπόνηση κατά τα πρώτα αναπτυξιακά στάδια στο λαβράκι (Dicentrarchus labrax)
Author Τσαλαφούτα, Αλέκα
Thesis advisor Παυλίδης, Μιχάλης
Reviewer Δερμών, Κατερίνα
Τζαμαρίας, Δημήτρης
Abstract The aims of this dissertation were to study the ontogeny of the endocrine stress response, to characterize the molecular programming of the Hypothalamus-Pituitary- Interrenal (HPI) axis, and to determine the impact of long term chronic mild stress applied early in life on the performance of fish at subsequent stages of development, in a Mediterranean marine teleost, the European sea bass (Dicentrarchus labrax). Sea bass embryos, pre-larvae and larvae at specific points of development were exposed to acute stressors and the temporal patterns of cortisol and α-MSH whole body concentrations and the expression of genes involved in corticosteroid biosynthesis, degradation and both cortisol and α-MSH signaling were determined. Expression of genes involved into the corticoid response regulation (gr1, gr2, mr, crf) combined with histological data indicated that, although a cortisol stress response is evident for the first time around first feeding, a pattern becomes progressively established in larvae at flexion until the formation of all fins. Moreover, mRNA transcript levels of 11β-hydroxylase and 11β-hsd2 which are involved in cortisol synthesis and deactivation/metabolism, respectively, showed a strong correlation with the whole body cortisol concentrations. An α-MSH stress response, an additional to cortisol pathway regulating stress in teleosts, is evident for the first time in the early development of European sea bass at the stage of mouth opening showing a specific pattern characterized by elevated levels that becomes established around the formation of all fins. mRNA transcript levels of pomc and mc2r were altered after the acute stress application in a consistent elevated pattern especially as development proceeds, at the stages of flexion and after the formation of all fins, showing at the 2 same time a similar pattern with the whole body α-MSH concentrations. The acute stress application had no effect on the expression of mc1r but in the case of mc4r resulted in an increased transcription even as early as at the stage of mouth opening. In fish, stress research is focused on the effects of acute or chronic severe noxius stimuli of physical, chemical and husbandry nature applied in juveniles or adult individuals, and there is no information on the effects of early exposure to long term chronic mild stressors on the development and performance of fish at subsequent phases of the life-cycle, but also no valid chronic low intensity stress protocol exists for fish at early development. To this end an unpredictable chronic low intensity stress (UCLIS) protocol was developed and evaluated for the first time in early development of E. sea bass. UCLIS protocol was based on the unpredictability, variety, frequency and moderate intensity of the applied stressors, providing a relatively realistic model of everyday aquaculture husbandry practices. The UCLIS application lasted for 14 consecutive days, starting at three different phases of early ontogeny (first feeding, flexion and development of all fins). Evaluation of the UCLIS protocol was performed through the determination of water-born cortisol concentrations of the larvae rearing tanks at regular intervals, recording of mortality and measurements of growth performance. In addition, its effects on subsequent developmental phases were evaluated by measurement of growth characteristics and by the determination of plasma cortisol in juvenile fish, prior and 1h after the application of an acute stressor. Our data show that European sea bass larvae are sensitive to mild husbandry stimuli with consequences even at subsequent phases of the life-cycle, with the stages of first feeding and all fins being the most critical, pointing out the necessity to reconsider common rearing practices. In particular, UCLIS application resulted in higher water 3 cortisol release rates in all groups where the stress was applied compared to the controls, proving to be a reliable non-invasive indicator of stress even during early ontogeny. Performance of fish in terms of growth rate was also affected by application of the stress protocol, as larvae that had been exposed to UCLIS at the beginning of first feeding and the formation of all fins displayed worst performance than fish exposed to UCLIS at flexion and controls. Early life stress did not affect plasma cortisol levels of juveniles exposed to additional acute stressors. However, fish were very sensitive to common handling practices and in addition, significant higher plasma cortisol concentrations were found in juveniles exposed to UCLIS at the stages of first feeding and the formation of all fins, compared to the other two groups, in accordance with the differences observed in growth rates. Concluding, the data obtained from this study provide a better insight into the onset and regulation of the stress response in early development of E. sea bass and show for the first time that early life stress, in the form of common husbandry practices, has an impact both on larvae performance and also on later stages of the life-cycle in this species, as life history affected the growth performance and the stress response in juvenile fish.
Language English
Subject Chronic acute
Χρόνιο οξύ
Issue date 2015-03-05
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Biology--Doctoral theses
  Type of Work--Doctoral theses
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