Development Of European Sea Bass Research Articles

Metabolomics analysis of the effects of temperature on the growth and development of juvenile European seabass (Dicentrarchus labrax)

Temperature variations have significant impacts on the growth and development of fish. In this study, the effects of temperature on the growth and development of European seabass (Dicentrarchus labrax) were investigated using ultra-performance liquid chromatography–tandem mass spectrometry-based metabolomics. Three groups of fish were exposed to various temperatures for 60 days: T1-E (10 °C), T2-E (15 °C), and T3-E (20 °C). Afterward, the temperature of all groups was increased to 20 °C and maintained for 62 days (T1-S, T2-S, T3-S). The livers were extracted for subsequent analysis. In the first stage of the experiment, the growth rate was highest in the T3-E group, followed by the T1-E and T2-E groups. The following metabolites identified by comparative analysis were found to be elevated: L-thyroxine, cysteamine, uridine diphosphate (UDP)-glucose, α-ketoglutaric acid, carbamoyl phosphate, and guanidine acetic acid of the T1-E group. Pathway analysis of the altered metabolites suggested changes in glucose metabolism, arginine and proline metabolism, the tricarboxylic acid cycle, the ornithine cycle, histidine metabolism, and taurine metabolism, which were involved with growth and development. Meanwhile, partial compensatory growth was observed in fish in the T1-S and T2-S groups. Metabolites identified as potential markers of growth included L-cysteine, taurocholic acid, UDP-glucose, and L-thyroxine. The significantly changed metabolic pathways were cysteine and methionine metabolism, bile secretion, tyrosine metabolism, and hypotaurine metabolism. We screened out the marker metabolites and metabolic pathway could provide important insights into the potential mechanisms of temperature affects the growth and development of European seabass. All in all, our research can provide theoretical basis and technical guidance for efficiently culturing European seabass.

\u03b1-MSH and melanocortin receptors at early ontogeny in European sea bass (Dicentrarchus labrax, L.)

Temporal patterns of whole-body α-MSH concentrations and of transcripts of melanocortin receptors during early development as well as the endocrine response (α-MSH, cortisol, MCR mRNAs) to stress at the end of the larval period were characterized in Dicentrarchus labrax. Immunohistochemistry showed α-MSH positive cells in the pituitary pars intermedia in all stages examined. As development proceeds, α-MSH content gradually increases; mRNA levels of mc2r and mc4r remain low until first feeding where peak values are observed. Mc1r expression was constant during development, pomc mRNA levels remain low until the stage of flexion after which a significant increase is observed. At the stage of the formation of all fins, whole-body cortisol and α-MSH concentrations responded with peak values at 2 h post stress. Additionally, the stress challenge resulted in elevated transcript levels of pomc, mc2r and mc4r but not in mc1r, with a pattern characterized by peak values at 1 h post stress and a strong correlation with whole body α-MSH concentrations was found. Our data provide for the first time a view on the importance of the α-MSH stress response in early development of European sea bass, an additional and relatively poorly understood signal involved in the stress response in teleosts.

Early life stress and effects at subsequent stages of development in European sea bass (D. labrax)

Abstract To investigate the effects of exposure to long term chronic mild stressors during early development on larvae and juvenile performance and cortisol stress response, an unpredictable chronic low intensity stress (UCLIS) protocol was developed for the first time and evaluated in European sea bass, Dicentrarchus labrax . 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. UCLIS lasted for 14 consecutive days, starting at different phases of early ontogeny (first feeding, flexion and development of all fins). Evaluation 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 30 min 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 stages of development, with the stages of first feeding and all fins being the most critical, providing the necessity to reconsider common rearing practices. In particular, UCLIS application resulted in higher water cortisol release rates in all groups compared to the controls proved to be a reliable non-invasive indicator of stress even during early ontogeny. Performance of fish in terms of survival, total length and wet weight was also affected by 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 compared to fish exposed to UCLIS at flexion and compared to the 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 practice and in addition, significant higher plasma cortisol concentrations were found in juveniles exposed to UCLIS at the stages of first feeding and onwards to flexion and the formation of all fins and onwards to the development of melanophores, compared to the other two groups in accordance with the differences observed in growth rates. Concluding, our data show for the first time that common husbandry practices during early development have an impact both on larvae performance and at later stages of development, as life history affected growth and the stress response in juvenile fish.

Whole body cortisol and expression of HSP70, IGF-I and MSTN in early development of sea bass subjected to heat shock

Whole body cortisol levels were determined during early larval developmental stages of sea bass ( Dicentrarchus labrax) subjected to a heat shock with the aim to investigate the correlation between the stress event and the activation of the hypothalamic–pituitary–interrenal axis. Moreover, the mRNA expression of inducible heat shock protein 70 (HSP70), insulin-like growth factor I (IGF-I) and myostatin (MSTN) was also detected. Whole body cortisol was determined by a radio-immunoassay (RIA) technique whereas the expression of HSP70, IGF-I and MSTN mRNAs was quantified by Real-Time PCR. Cortisol was detectable in all the larvae from hatching but its level increased significantly in larvae submitted to heat shock from 2-day post hatching onwards. An effect of the sole transfer on cortisol levels was detectable at day 10, indicating an increase of the hypothalamic–pituitary–interrenal axis sensitivity from this stage of sea bass development. In animals exposed to heat shock, the expression of inducible HSP70 resulted in a marked increase of mRNA levels already at hatching. This increase was significantly higher from 6 days onwards if compared to controls. Moreover, heat shock resulted in a decrease (although not significant) in IGF-I mRNA expression of stressed larvae if compared to controls. On the contrary, heat shock did not influence the expression of MSTN mRNA in all groups. The results indicate a very early activation of the hypothalamic–pituitary–interrenal axis and in general of the stress response during the development of European sea bass. Moreover, these results suggest the importance of cortisol and inducible HSP70 as bioindicators of stress in aquaculture and confirm the role of IGF-I and MSTN as regulatory factors during development and growth of fish.

Mechanisms of oocyte development in European sea bass (Dicentrarchus labrax L.): investigations via application of unilateral ovariectomy

Unilateral ovariectomy (ULO) was performed in European sea bass (Dicentrarchus labrax L.) during late pre-vitellogenesis/early vitellogenesis. Plasma steroid levels and the expression of a suite of potential oogenesis-relevant genes in the ovary, brain, and pituitary were evaluated with the aim of understanding their involvement in the compensatory oocyte development occurring within the remaining ovarian lobe. After 69 days of surgery the remaining ovarian lobe in ULO fish was gravimetrically equivalent to an intact-paired ovary of sham operated, control fish. This compensatory ovarian growth was based on an increased number of early perinucleolar oocytes and mid-late stage vitellogenic follicles without an apparent recruitment of primary oocytes into the secondary growth phase. Plasma steroid levels were similar in ULO and control females at all time points analyzed, suggesting an increased steroid production of the remaining ovarian lobe in hemi-castrated females. Results of the gene expression survey conducted indicate that the signaling pathways mediated by Fsh and Gnrh1 constitute the central axes orchestrating the observed ovarian compensatory growth. In addition, steroid receptors, Star protein, Igfs, and members of the transforming growth factor beta superfamily including anti-Mullerian hormone and bone morphogenetic protein 4 were identified as potentially relevant players within this process, although their specific actions and interactions remain to be established. Our results demonstrate that ULO provides an excellent in vivo model for elucidating the interconnected endocrine and molecular mechanisms controlling oocyte development in European sea bass.

Imbalanced dietary ascorbic acid alters molecular pathways involved in skeletogenesis of developing European sea bass ( Dicentrarchus labrax)

The influence of dietary ascorbic acid (AA) on growth and morphogenesis during the larval development of European sea bass ( Dicentrarchus labrax) was evaluated until 45 days post hatching. Diets incorporated 0, 5, 15, 30, 50 or 400 mg AA per kg diet to give AA-0, AA-5, AA-15, AA-30, AA-50 and AA-400 dietary treatments, respectively. Dietary AA levels lower than 15 mg/kg reduced larval growth and survival was affected in specimens fed diets devoid of AA. Globally, disruption of the expression of genes involved in AA and calcium absorption in the intestine (SVCT-1, TRPV-6), skeletogenesis (BMP-4, IGF-1, RARγ) and bone mineralization (VDRβ, osteocalcin) were observed in groups fed doses lower and higher than 50 mg AA/kg diet. Such disturbances detected at molecular level were associated with disruptions of the ossification process and the appearance of skeletal abnormalities.

Dietary vitamin D 3 affects digestive system ontogenesis and ossification in European sea bass ( Dicentrachus labrax, Linnaeus, 1758)

The influence of dietary vitamin D 3 (VD 3) on survival, growth and morphogenesis during the larval development of European sea bass ( Dicentrarchus labrax) was evaluated until 45 days post hatching. Diets contained 4% of the standard vitamin mix (VM) recommended by the National Research Council (NRC) and incorporated 0, 19.2, 38.4, or 140 IU of VD 3 per gram of diet to give VD-0, VD-1, VD-2 and VD-3 dietary treatments, respectively. The present study revealed for the first time an impact of dietary VD 3 on the sea bass digestive system ontogenesis that consequently conditioned the ossification process and morphogenesis. All dietary VD 3 levels were in the “adequate range” based on larval survival. Nevertheless, growth, intestinal maturation and ossification at the end of the larval stage were harmed by the minimum dose of VD 3 tested and resulted in the appearance of malformations. VD-2 and VD-3 groups showed satisfactory growth and ossification levels at the end of the larval period. However, results of enzymatic activity and expression of genes involved in the VD 3 pathway (bone morphogenetic protein 4, osteocalcin, vitamin D receptors and transient receptor potential cation channel-subfamily V, member 6-) gave evidence of complications during the ossification process as revealed by the high percentage of deformed larvae. A VD 3 level of 19.2 IU/g diet appeared necessary to obtain harmonious larval morphogenesis.

Gene Expression Patterns During the Larval Development of European Sea Bass (Dicentrarchus Labrax) by Microarray Analysis

During the larval period, marine teleosts undergo very fast growth and dramatic changes in morphology, metabolism, and behavior to accomplish their metamorphosis into juvenile fish. Regulation of gene expression is widely thought to be a key mechanism underlying the management of the biological processes required for harmonious development over this phase of life. To provide an overall analysis of gene expression in the whole body during sea bass larval development, we monitored the expression of 6,626 distinct genes at 10 different points in time between 7 and 43 days post-hatching (dph) by using heterologous hybridization of a rainbow trout cDNA microarray. The differentially expressed genes (n = 485) could be grouped into two categories: genes that were generally up-expressed early, between 7 and 23 dph, and genes up-expressed between 25 and 43 dph. Interestingly, among the genes regulated during the larval period, those related to organogenesis, energy pathways, biosynthesis, and digestion were over-represented compared with total set of analyzed genes. We discuss the quantitative regulation of whole-body contents of these specific transcripts with regard to the ontogenesis and maturation of essential functions that take place over larval development. Our study is the first utilization of a transcriptomic approach in sea bass and reveals dynamic changes in gene expression patterns in relation to marine finfish larval development.

Temporal profile of brain and pituitary GnRHs, GnRH-R and gonadotropin mRNA expression and content during early development in European sea bass ( Dicentrarchus labrax L.)

A likely endocrine control mechanism for sexual differentiation in size-graded populations of European sea bass ( Dicentrarchus labrax) is proposed by evaluating the brain expression and pituitary content of two forms of gonadotropin-releasing hormone (GnRH), namely sea bream (sbGnRH) and salmon (sGnRH), the pituitary expression of one subtype of GnRH receptor (dlGnRH-R-2A) and the three gonadotropin (GtH) subunits, namely glycoprotein α (GPα), follicle-stimulating hormone β (FSHβ) and luteinizing hormone β (LHβ), as well as the pituitary and plasma LH levels between 50 and 300 days post-hatching (dph). Four gradings were conducted between 2 and 8 months after hatching, resulting in a population of large and small individuals, having 96.5% females (female-dominant population) and 69.2% males (male-dominant population), respectively, after the last grading. The onset of gonadal differentiation was different in the two sexes, and coincided with a peak of expression of sbGnRH or sGnRH. Furthermore, the expression of these GnRHs was correlated with the expression of dlGnRH-R-2A. Sex-related differences in the brain and pituitary content of sbGnRH were also found at the time of sexual differentiation. Moreover, the observed sexual dimorphism at the transcriptional or synthesis level of these GnRH forms suggests that a different neuro-hormonal regulation is operating according to sex. At the onset of sex differentiation, FSHβ transcriptional activity reached maximal values, which were maintained until the completion of the process. The present study suggests a role for sbGnRH, sGnRH and the dlGnRH-R-2A during gonadal differentiation, possibly through enhancement of FSHβ gene expression. In males, a different endocrine regulation seems to exist also during spermiogenesis and spermiation, when gene transcription, peptide synthesis and release of LH are of greater importance.

Drinking and Na +/K + ATPase activity during early development of European sea bass, Dicentrarchus labrax: Ontogeny and short-term regulation following acute salinity changes

The short-term osmoregulatory capacity of sea bass ( Dicentrarchus labrax) larvae and juveniles at consecutive developmental stages was evaluated by an analysis of drinking rates and whole-body and branchial Na +/K + ATPase activity. The effect of acute salinity stress on those parameters was assessed from hatching to the juvenile stage. Drinking rate normalised to body weight (DR bw) decreased throughout postembryonic development. DR bw was not affected by salinity in yolk sac larvae. However, significant differences were observed in older larvae and in juveniles submitted to hypo- and hyperosmotic challenges. Post yolk sac larvae and juveniles always drink, but at a lower rate in hypoosmotic media compared to hyperosmotic media. A correlation was established between DR bw and blood osmolality during the postembryonic development of the sea bass. Na +/K + ATPase specific and total activity in whole larval homogenates decreased from hatching to the 5-mm yolk sac larva stage and increased in 10-mm stage larvae. The enzyme specific activity in the gills, from post yolk sac larvae to juveniles, decreased whereas the total activity increased during the same period. Developing sea bass have a better capacity to cope with hypoosmotic than hyperosmotic media.