Juvenile Sea Bream Research Articles

A long-term growth hormone treatment stimulates growth and lipolysis in gilthead sea bream juveniles

The enhancement of the endocrine growth hormone (GH)/insulin-like growth factor I (IGF-I) system by the treatment with a sustained release formulation of a recombinant bovine GH (rBGH), is a good strategy to investigate growth optimization in aquaculture fish species. To further deepen into the knowledge of rBGH effects in fish and to estimate the growth potential of juveniles of gilthead sea bream, the present work evaluated rBGH injection on growth, GH/IGF-I axis and lipid metabolism modulation, and explored the conservation of GH effects provoked by the in vivo treatment using in vitro models of different tissues. The rBGH treatment increased body weight and specific growth rate (SGR) in juveniles and potentiated hyperplastic muscle growth while reducing circulating triglyceride levels. Moreover, the results demonstrated that the in vivo treatment enhanced also lipolysis in both isolated hepatocytes and adipocytes, as well as in day 4 cultured myocytes. Furthermore, these cultured myocytes extracted from rBGH-injected fish presented higher gene expression of GH/IGF-I axis-related molecules and myogenic regulatory factors, as well as stimulated myogenesis (i.e. increased protein expression of a proliferation and a differentiation marker) compared to Control fish-derived cells. These data, suggested that cells in vitro can retain some of the pathways activated by in vivo treatments in fish, what can be considered an interesting line of applied research. Overall, the results showed that rBGH stimulates somatic growth, including specifically muscle hyperplasia, as well as lipolytic activity in gilthead sea bream juveniles.

Is dietary taurine required for white seabream (Diplodus sargus) juveniles?

This study assessed the effect of supplementation of low-fishmeal (FM) diets with taurine in white seabream (Diplodus sargus) juveniles. Four isoproteic (36% CP) and isolipidic (18% CL) diets were formulated to include 15%FM or 5%FM, supplemented or not with 1% of Taurine (TAU). Twelve groups of 15 fish (IBW = 58 g) were fed each diet to near satiation for 10 weeks. Growth performance, feed intake, and feed efficiency were not affected by dietary FM level. Nevertheless, dietary TAU supplementation increased growth performance and feed efficiency. Nitrogen and energy retention were improved by both dietary FM level and TAU supplementation. Plasma cholesterol, lactate, and bilirubin did not differ among dietary treatments, but dietary TAU supplementation decreased plasma glucose and triglycerides levels. Decrease of FM level reduced total bile salts while TAU supplementation had the opposite effect. No differences were noticed in innate immune parameters assessed. Overall, results indicate that white seabream can be fed with diets almost devoid of FM, and that dietary TAU supplementation increases growth performance and feed efficiency. Moreover, results suggest that dietary TAU was limiting both in 15% and 5% FM diets.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes.

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1–6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.

Soybean meal replacement by corn distillers dried grains with solubles (DDGS) and exogenous non-starch polysaccharidases supplementation in diets for gilthead seabream (Sparus aurata) juveniles

A growth trial was conducted to evaluate the effect of dietary plant-protein replacement by corn distillers dried grains with solubles (DDGS), and of exogenous carbohydrases supplement (Natugrain®TS, BASF) in gilthead seabream (Sparus aurata) juveniles. For that purpose, a basal diet was formulated with 35% of fish meal and 20% soybean meal (SBM) as main protein sources. Two other diets were formulated incorporating 15 or 35% of DDGS, replacing 37.5% or 100% of SBM (diets DDGS15 and DDGS35, respectively). Another diet was formulated similar to diet DDGS35 and supplemented with 0.1% of a commercial non-starch polysaccharidases complex, Natugrain®TS, BASF (CHOase; diet DDGS35ENZ). Triplicate groups of fish (IBW = 15 ± 1 g) were fed the experimental diets for 67 days at 22 °C. At the end of the trial, growth performance, voluntary feed intake, feed efficiency, protein and energy retention were not affected by dietary DDGS incorporation. Dietary CHOase supplementation also did not affect growth performance, but increased feed efficiency, nitrogen and energy retention. Dietary inclusion of DDGS tended to decrease production cost (€ per kg of fish), and dietary CHOase supplementation further reduced production cost, which was significantly lower with diet DDGS35ENZ than with the basal diet. Whole-body composition, hepatosomatic and visceral indexes were not affected by the dietary inclusion of DDGS, though a trend was noticed for a decrease of whole-body lipid, energy, and visceral index with the increase dietary DDGS. Plasma glucose, protein, albumin, and globulins levels were similar among diets, whereas plasma triglycerides increased, and cholesterol decreased with the increase of dietary DDGS. Hepatic glycolytic enzymes activities (hexokinase and glucokinase) were similar among groups, while gluconeogenic (fructose biphosphatase) activity, GDH and ASAT activities decreased with the increase of dietary DDGS. The hepatic activity of oxidative stress-related enzymes catalase and superoxide dismutase were not affected by dietary treatments, but G6PDH and GR activities decreased, and liver lipid peroxidation increased with dietary DDGS level. Dietary CHOase supplementation decreased overall lipid peroxidation.Overall, results of this study indicate that total replacement of SBM by DDGS in diets for gilthead seabream did not compromise growth performance or feed utilization efficiency, while supplementation of DDGS-based diet with exogenous carbohydrases improved feed utilization efficiency and economic efficiency ratio.

Effects of dietary tryptophan and chronic stress in gilthead seabream (Sparus aurata) juveniles fed corn distillers dried grains with solubles (DDGS) based diets

Distillers' dried grains with solubles (DDGS) has low tryptophan (Trp) relatively to the branched-chain amino acids (BCAA) levels, and this may reduce transport of Trp through the blood-brain barrier due to competition for the same transport carrier. This may affect synthesis and release of serotonin, with negative consequences in stress tolerance. In the present study, it is hypothesized that a Trp/BCAA unbalance in high DDGS diets may impair the capacity of gilthead seabream (Sparus aurata) juveniles to cope with chronic stress induced by high stocking density. Three DDGS-based diets (30%DDGS+13%FM) were formulated and supplemented with Trp at 0, 0.13, and 0.25% of the diet and tested in triplicate, at two initial stocking densities (5 and 16 kg m−3), in a 2 × 3 total randomized factorial design. The growth trial was performed with 12 g fish and lasted 64 days. Irrespective of the diet, high stocking density reduced growth performance and feed intake, but not feed efficiency. Plasma protein, triglycerides, and cholesterol levels; whole-body lipid, hepatosomatic index, and liver glycogen; hepatic activity of key-enzymes of glycolysis and lipogenesis were also reduced. Moreover, plasma glucose level and hepatic activity of key-enzymes gluconeogenesis were increased.Irrespective of stocking density, diets supplementation with Trp did not affect growth and feed efficiency, but increased hepatic lipase activity and reduced liver lipids, plasma triglycerides and cholesterol levels, and hepatic activity of key-enzymes of amino acid catabolism. Moreover, dietary Trp supplementation restored plasma glucose levels of fish kept at high stocking density to levels similar to that of fish kept at low stocking density.Overall, present results indicate that high stocking density reduced growth performance without affecting feed efficiency of gilthead seabream. Dietary Trp supplementation did not counteract the negative effect of stocking density on growth performance but seemed to mitigate stress response of gilthead seabream juveniles kept at high stocking density.

Ghrelin and Its Receptors in Gilthead Sea Bream: Nutritional Regulation.

Ghrelin is involved in the regulation of growth in vertebrates through controlling different functions, such as feed intake, metabolism, intestinal activity or growth hormone (Gh) secretion. The aim of this work was to identify the sequences of preproghrelin and Ghrelin receptors (ghsrs), and to study their responses to different nutritional conditions in gilthead sea bream (Sparus aurata) juveniles. The structure and phylogeny of S. aurata preproghrelin was analyzed, and a tissue screening was performed. The effects of 21 days of fasting and 2, 5, 24 h, and 7 days of refeeding on plasma levels of Ghrelin, Gh and Igf-1, and the gene expression of preproghrelin, ghsrs and members of the Gh/Igf-1 system were determined in key tissues. preproghrelin and the receptors are well conserved, being expressed mainly in stomach, and in the pituitary and brain, respectively. Twenty-one days of fasting resulted in a decrease in growth while Ghrelin plasma levels were elevated to decrease at 5 h post-prandial when pituitary ghsrs expression was minimum. Gh in plasma increased during fasting and slowly felt upon refeeding, while plasma Igf-1 showed an inverse profile. Pituitary gh expression augmented during fasting reaching maximum levels at 1 day post-feeding while liver igf-1 expression and that of its splice variants decreased to lowest levels. Liver Gh receptors expression was down-regulated during fasting and recovered after refeeding. This study demonstrates the important role of Ghrelin during fasting, its acute down-regulation in the post-prandial stage and its interaction with pituitary Ghsrs and Gh/Igf-1 axis.

Dietary krill meal inclusion contributes to better growth performance of gilthead seabream juveniles

There is a need to find sustainable alternatives to fishmeal (FM) and fish oil (FO) in feed formulations to support the continued growth of aquaculture. FM is mostly produced from mass-caught pelagic species, but the production has been relatively constant for several decades. The aim of this study was to investigate the potential of dietary krill meal (KM) inclusion as a sustainable alternative to FM. In view of that, a feeding trial with gilthead seabream juveniles was conducted to evaluate whether dietary KM at 3%, 6% and 9% inclusion improves growth performance in comparison with a control diet. At the end of the study, fish in the 9% KM group showed significantly higher body weight (32.76 g) compared with fish fed the control diet (30.30 g). Moreover, FM replacement by 9% KM indicated a reduction in the accumulation of lipid droplets in the hepatocytes and around the pancreatic islets. In summary, this study suggests that FM can be reduced in diets for seabream without negatively affecting growth performance, when KM is added. On the contrary, KM enhances gilthead seabream growth and reduces lipid accumulation and damage of hepatocytes, which will open an interesting innovation line to completely replace FM by alternative terrestrial protein sources and the partial inclusion of KM.

Genetics of resistance to photobacteriosis in gilthead sea bream (Sparus aurata) using 2b-RAD sequencing

BackgroundPhotobacteriosis is an infectious disease developed by a Gram-negative bacterium Photobacterium damselae subsp. piscicida (Phdp), which may cause high mortalities (90–100%) in sea bream. Selection and breeding for resistance against infectious diseases is a highly valuable tool to help prevent or diminish disease outbreaks, and currently available advanced selection methods with the application of genomic information could improve the response to selection. An experimental group of sea bream juveniles was derived from a Ferme Marine de Douhet (FMD, Oléron Island, France) selected line using ~ 109 parents (~ 25 females and 84 males). This group of 1187 individuals represented 177 full-sib families with 1–49 sibs per family, which were challenged with virulent Phdp for a duration of 18 days, and mortalities were recorded within this duration. Tissue samples were collected from the parents and the recorded offspring for DNA extraction, library preparation using 2b-RAD and genotyping by sequencing. Genotypic data was used to develop a linkage map, genome wide association analysis and for the estimation of breeding values.ResultsThe analysis of genetic variation for resistance against Phdp revealed moderate genomic heritability with estimates of ~ 0.32. A genome-wide association analysis revealed a quantitative trait locus (QTL) including 11 SNPs at linkage group 17 presenting significant association to the trait with p-value crossing genome-wide Bonferroni corrected threshold P ≤ 2.22e-06. The proportion total genetic variance explained by the single top most significant SNP was ranging from 13.28–16.14% depending on the method used to compute the variance. The accuracies of predicting breeding values obtained using genomic vs. pedigree information displayed 19–24% increase when using genomic information.ConclusionThe current study demonstrates that SNPs-based genotyping of a sea bream population with 2b-RAD approach is effective at capturing the genetic variation for resistance against Phdp. Prediction accuracies obtained using genomic information were significantly higher than the accuracies obtained using pedigree information which highlights the importance and potential of genomic selection in commercial breeding programs.

Net-chasing training improves the behavioral characteristics of hatchery-reared red sea bream (Pagrus major) juveniles

The low return rate of fish released for stock enhancement has often been attributed to hatchery-reared fish having inferior behavioral characteristics. We tried to improve the behavioral characteristic of red sea bream (Pagrus major) juveniles by using a net-chasing treatment. The fish were provided with 2 min of net chasing twice daily for 3 weeks, following which their behavioral characteristics (emergence from a start area, avoidance response to novel stimulus, and foraging following transfer between tanks) were individually tested and compared with a control group. A predator exposure test was then conducted using marbled rockfish (Sebastiscus marmoratus). Net-chased fish exhibited a shorter latency to emergence, a higher avoidance rate, and an earlier foraging time than the control fish, indicating that the net-chasing treatment may improve adaptability for environmental change and alertness to a novel object. The net-chased fish also exhibited a better survival rate than the control fish, with an odds ratio of 6.76. We suggest that net-chasing training represents an easy and efficient method for improving the behavior of fish for stock enhancement.

Feed pellets containing chitosan nanoparticles as plasmid DNA oral delivery system for fish: In vivo assessment in gilthead sea bream (Sparus aurata) juveniles

The aim of this study was the assessment of preloaded feed pellets as a delivery system for plasmid DNA (pDNA), with the purpose of evaluating the potential administration of DNA vaccines orally in aquacultured fish. Pellets were made up by usual feed ingredients, which were mixed with chitosan nanoparticles entrapping a model plasmid (pCMVβ) expressible in eukaryotic cells before being elaborated. The plasmid is characterized by the insertion of the reporter gene lacZ, encoding for the bacterial enzyme β-galactosidase (β-gal). The possible in vivo expression of the exogenous gene was measured in different fish tissues of gilthead sea bream (Sparus aurata) juveniles by two different procedures. On the one hand, the activity of the enzyme β-gal was detected and quantified in muscle, liver and intestine; on the other, specific IgM against β-gal antigen was titrated in blood samples. Intramuscular (i.m.) injection of equal amounts of plasmid was also carried out for the purpose of comparison with oral administration. The expression of the reporter gene was detected in fish tissues following both oral and i. m. administration of pDNA up to 60 days. However, organ distribution of the gene expression was more evident after oral (β-gal activity measured in gut, liver and muscle) than after parenteral administration (restricted to adjacent muscle tissues). In agreement, specific IgM titration indicated that humoral immune response was more intense and sustained throughout the experimental period after oral than after i. m. delivery of equal amounts of pDNA. These results suggest that feed pellets containing chitosan nanoparticles might enable efficient oral delivery of pDNA, a fact that might imply valuable applications in terms of on-farm mass immunization purposes, especially with regard to DNA-based vaccines and small size fish, in which i. m. administration remains unfeasible.

Acoustic Conditioning System Development and Conditioning Experiments on Black Seabreams in the Xiangshan Bay Sea Ranch

Attracting released hatchery-reared fish to designated areas during the growth process is vital to realize the objectives of sea ranching. Based on the bottom artificial reefs and surface kelp culture facilities in the Xiangshan Bay sea ranch, we proposed systematic techniques related to acoustic conditioning of the black seabream (Sparus macrocephalus). Experiments conducted in 12 m × 10 m × 1.6 m ponds on Xixuan Island showed that black seabream was positively sensitive to 500–600 Hz periodic signals. Conditioned responses were apparent after 8 d. Two to three days were required for recovery of the memory of a conditioned response after a 20-day interval. According to the practical application requirements in the open sea, unattended acoustic conditioning equipment was developed. The ranching equipment was used in 12 m × 12 m × 2.5 m cages, and the behavior of black seabream juveniles was successfully guided after 7 days. Of the 16000 released fish, 82.5% of them were conditioned with a flexible grading net. To avoid inducing a stress response, the juveniles were released into the sea ranch in situ from the net cage. The acoustic conditioning equipments were moved into the open sea and the aggregation phenomenon of the released fish was observed when the sound was played. After 6 months of investigation and based on Sr+ marking, only one acoustically conditioned fish was found outside the 3.5-km2 sea ranch area, thereby reached the goal of guiding activity. The practical effect in the Xiangshan Bay sea ranch showed the validity of the acoustic conditioning system, which may contribute to improve the operation of the sea ranches in the East China Sea.

Inclusion of poultry by-product meal in the diet of Sparidentex hasta: Effects on production performance, digestibility and nutrient retention

A 60-day experiment was conducted to evaluate the effect of replacement of fish meal (FM) with poultry by-product meal (PBM) on growth performance and feed utilization of juvenile sobaity sea bream (Sparidentex hasta). PBM replaced 0, 15, 25, 35, 45 and 55% of dietary FM in the isoproteic (500 g kg−1) and isocaloric (21 kj g−1) experimental diets. Sobaity sea bream with an average initial weight of 29.27 ± 0.06 g were randomly assigned to 18 tanks (6 treatments with triplicates each) at an initial stocking density of 20 fish per tank. The final body weight, weight gain, specific growth rate, protein efficiency ratio and nitrogen retention efficiency were higher in fish fed PBM15, 25 and 35 diets than in fish fed the control, PBM45 and 55 diets. Feed conversion ratio, nitrogen and phosphorus wastage did not show significant differences in PBM0, 35, 45 and 55. Increased retention of arginine, lysine, methionine, histidine and taurine was observed at lower dietary content of the respective amino acids. The morphometric indices, body proximate composition and amino acid profile were not significantly affected by the dietary treatments. Apparent digestibility coefficients (ADC) of dry matter, lipid and calcium in fish fed PBM diet did not show significant differences with PBM0. Protein ADC was significantly decreased with increased PBM level from 35%. Our results indicated that using fish meal and PBM in combination lead to improved growth and feed utilization of sobaity sea bream when compared to treatments using FM alone as the dietary protein source. Fish meal protein could be replaced up to 55% by PBM in the formulated diets of S. hasta juveniles without any negative effects on growth performance, feed utilization and whole body amino acid profile.

Effect of Dietary Essential Oils Supplementation on Growth Performance, Nutrient Utilization, and Protein Digestibility of Juvenile Gilthead Seabream Fed a Low‐Fishmeal Diet

AbstractThe present study aimed to assess the efficacy of supplemental plant essential oils (PEOs) on the growth performance and digestive processes of juvenile gilthead seabream. Three experimental diets were tested: (1) a control (CTRL) diet formulated with low marine‐derived protein level (19%); (2) CTRL diet supplemented with a blend of anise, citrus, and oregano essential oils at 1.2 g/kg (diet Phyto C); and (3) CTRL diet supplemented with a similar blend at 0.2 g/kg, but in encapsulated form (diet Phyto E). Triplicate groups of 20 fish (mean initial body weight = 27.9 ± 2.1 g) were fed the experimental diets over 63 d. Results showed that specific growth rate, voluntary feed intake, feed conversion ratio, and protein efficiency ratio were not significantly affected by the two dietary supplements. The commercial blend of PEOs tested here can be successfully incorporated into a low‐fishmeal diet to maximize protein and fat retention and to minimize nitrogenous losses in seabream juveniles. Phyto E presented a decrease in nitrogenous metabolic and fecal losses. The practical implications of including this plant‐based blend in aquafeeds can potentially include faster fish growth and improved production time, but these remain to be tested in a longer experimental trial.

Disposition of a Glucose Load into Hepatic Glycogen by Direct and Indirect Pathways in Juvenile Seabass and Seabream

In carnivorous fish, conversion of a glucose load to hepatic glycogen is widely used to assess their metabolic flexibility towards carbohydrate utilization, but the activities of direct and indirect pathways in this setting are unclear. We assessed the conversion of an intraperitoneal glucose load (2 g.kg−1) enriched with [U-13C6]glucose to hepatic glycogen in juvenile seabass and seabream. 13C-NMR analysis of glycogen was used to determine the contribution of the load to glycogen synthesis via direct and indirect pathways at 48-hr post-injection. For seabass, [U-13C6]glucose was accompanied by deuterated water and 2H-NMR analysis of glycogen 2H-enrichment, allowing endogenous substrate contributions to be assessed as well. For fasted seabass and seabream, 47 ± 5% and 64 ± 10% of glycogen was synthesized from the load, respectively. Direct and indirect pathways contributed equally (25 ± 3% direct, 21 ± 1% indirect for seabass; 35 ± 7% direct, 29 ± 4% indirect for seabream). In fasted seabass, integration of 2H- and 13C-NMR analysis indicated that endogenous glycerol and anaplerotic substrates contributed an additional 7 ± 2% and 7 ± 1%, respectively. In fed seabass, glucose load contributions were residual and endogenous contributions were negligible. Concluding, direct and indirect pathways contributed equally and substantially to fasting hepatic glycogen repletion from a glucose load in juvenile seabream and seabass.

Gut microbiota and gut morphology of gilthead sea bream (Sparus aurata) juveniles are not affected by chromic oxide as digestibility marker

The present work aimed to evaluate whether the use of chromic oxide (Cr2O3) as dietary inert marker in fish digestibility studies interferes with gut microbial community modulation and gut morphology. To assess the effects of Cr2O3 under potential diverse microbiota populations, dietary Cr2O3 was tested using challenging plant feedstuffs (PF)-based diets supplemented or not with prebiotics, as prebiotics are expected to modify gut microbiota populations. For that purpose, three diets were formulated to include circa 20:80 fish meal and PF as protein sources, without (CTR) or with prebiotic supplementation (10 g/kg XOS or GOS). These diets did not include Cr2O3 (−Cr2O3 diets). Three similar additional diets were formulated to include 5 g/kg Cr2O3 (+Cr2O3 diets). Cr2O3 effects on gut microbiota were assessed for the first time in the allochthonous (digesta) and autochthonous (mucosa) community by a culture-independent molecular approach, using denaturing gradient gel electrophoresis (DGGE). No differences in gut bacterial profiles (number of operational taxonomic units, microbiota richness, diversity and similarity indices) were observed between dietary treatments. No significant alterations in submucosa layer structure, enterocytes and eosinophilic granular cells structure, goblet cells and leucocytes quantity were detected in the distal intestine among diets. In conclusion, data indicate that dietary inclusion of 5 g/kg Cr2O3 does not interfere with gilthead sea bream (Sparus aurata) gut microbiota and gut morphology, suggesting that a dietary incorporation level of 5 g/kg Cr2O3 can safely be used as inert marker in digestibility studies.

Intraspecific cleaning by juvenile Cape white seabream Diplodus capensis (Sparidae) off eastern South Africa

Juveniles of the Cape white seabream Diplodus capensis were observed cleaning adult conspecifics in a large tidepool off Sodwana Bay, South Africa. Although nine other tropical fish species were present and interacted with a nearby pair of Labroides cleaner wrasses, only adults of D. capensis posed for and were cleaned by the D. capensis juveniles. Such cleaning interactions have not been reported previously for this species or among marine fishes off South Africa, and thus add to the growing list of facultative cleaners globally.

Evaluation of defatted krill meal as partial and total fishmeal replacement in diets for gilthead seabream (Sparus aurata) juveniles

Evaluation of defatted krill meal as partial and total fishmeal replacement in diets for gilthead seabream (Sparus aurata) juveniles

Effect of colored light regimes on the stress response and RNA/DNA ratio of juvenile red sea bream, Pagrus major

We hypothesized that fish with red-sensitive retina would be stressed by red light and thus inhibited in somatic growth. Red sea bream (Pagrus major) juveniles (total length =3 cm) with red-sensitive retina were chosen to test this hypothesis. We examined the effect of different color lights (red with λmax 605 nm; green with λmax 540 nm; blue with λmax at 435 nm; and white with full spectrum) on unfed juveniles in laboratory tanks. Stress level was measured by the plasma cortisol and glucose concentrations, and nutritional status by muscle RNA/DNA ratio. Under red light, plasma cortisol and glucose, and muscle RNA/DNA were significantly higher than under green, blue, or white light. Our hypothesis was partly supported by previous findings on the effects of the color environment and spectral sensitivity of reared fishes. However, the levels of cortisol, glucose, and RNA/DNA in this study were low compared to published values. It seems that hatchery-bred juvenile red sea bream have adapted to red-rich surface light and are able to cope with the stress of living in surface floating cages which is so different from their deep-water habitats.

Inorganic, organic, and encapsulated minerals in vegetable meal based diets for Sparus aurata (Linnaeus, 1758).

Substituting fishmeal (FM) with vegetable meal (VM) can markedly affect the mineral composition of feeds, and may require additional mineral supplementation. Their bioavailability and optimal supplementation levels depend also on the form of delivery of minerals. The aim of the study was to determine the effect of different delivery forms of three major trace elements (Zn, Mn and Se) in a marine teleost. Gilthead sea bream juveniles of 22.5 g were fed a VM-based diet for 12 weeks that was either not supplemented with these minerals or supplemented with inorganic, organic, or encapsulated inorganic forms of minerals in triplicate and compared to a FM-based diet. Our results showed that mineral delivery form significantly affected the biochemical composition and morphology of posterior vertebrae. Supplementation of VM-based diets with inorganic forms of the target minerals significantly promoted growth, increased the vertebral weight and content of ash and Zn, enhanced bone mineralization and affected the vertebral shape. Conversely, encapsulation of inorganic minerals reduced fish growth and vertebral mineral content, whereas supplementation of organic minerals, enhanced bone osteogenesis by upregulating bone morphogenetic protein 2 (bmp2) gene and produced vertebrae with a larger length in relation to height. Furthermore, organic mineral forms of delivery downregulated the expression of oxidative stress related genes, such as Cu/Zn superoxide dismutase (Cu/Zn sod) and glutathione peroxidase 1 (gpx-1), suggesting thus that dietary minerals supplemented in the organic form could be reasonably considered more effective than the inorganic and encapsulated forms of supply.

Preliminary studies on haematological and plasmatic parameters in gilthead sea bream (Sparus aurata) held under day/night temperature variations

This study aimed to evaluate to what extent diel water temperature oscillations over a short period of time (41h) affected haematologic and plasmatic parameters of gilthead sea bream. Sea bream juveniles (160 fish; 177.2±20.9g) were divided in two homogenous groups, experimental and control. The experimental group was exposed to water at 22.3±0.6°C between 5a.m. and 5p.m. and to colder water from 5p.m. to 5a.m. (temperature variation of 8.6±0.3°C) during 41h period, whereas for the control group, water temperature was maintained constant (22.4±0.7°C) for the same period. Fish were fed three times per day (10:30a.m., 2p.m., 4p.m.). Blood was collected from fish caudal veins (n=6) at different time points (10a.m., 1p.m., 5p.m., 6:30p.m., 8p.m. and 10a.m. of the following day) from each group, for haematologic (haematocrit and haemoglobin) and plasmatic (glucose, cortisol, triglycerides and total protein) determinations. All parameters studied tended to vary throughout the study period, both for experimental and control groups. Significant differences were observed between the two groups for all the studied parameters at different sampling points. These differences were observed near the influence of the cold-water period or during the cooling-water period. Results suggested that colder water temperature cycles depressed fish metabolic activity and affected the levels of the analysed blood-circulating metabolites. Overall, results suggested that stress response was similar for experimental and control groups and that gilthead sea bream were able to cope with diel water temperature variations.