Μolecular and endocrine regulation of the stress response during early developmental stages in european sea bass (Dicentrarchus Labrax)

by Alexandra Tsalaouta

Institution: University of Crete (UOC); Πανεπιστήμιο Κρήτης
Year: 2015
Keywords: Καταπόνηση; Stress
Record ID: 1155523
Full text PDF: http://hdl.handle.net/10442/hedi/35371


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 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…