Intestinal l-methionine transport in the cultured gilthead bream (Sparus aurata)

• 1.1. The influx and transepithelial movements of l-methionine and its effects on the electrophysiology and Na-Cl-transport in upper and lower intestine of the cultured fish, Spanis aurata, were measured.
• 2.2. The K_m and V_max of l-methionine influx into the tissues were higher in lower intestine than in upper intestine. A prominent diffusion-like transport component was also measured in both segments during influx experiments.
• 3.3. Net transepithelial fluxes of l-methionine (1 mM) were observed in both upper and lower intestine, this transport being Na⁺-dependent.
• 4.4. The two intestinal segments exhibited an electrical potential difference (PD) and a short circuit current (I_sc) serosa negative or near zero. Tissue conductance (G_t) was higher in posterior than in lower intestine.
• 5.5. Addition of l-methionine to the mucosal side of lower or upper intestine did not induce changes in PD in either part.
• 6.6. Isotopic fluxes of Cl⁻ or Na⁺ measurements under short circuit conditions showed that there were no net Cl⁻ or Na⁺ transport in either part.
• 7.7. l-Methionine additions to the mucosa did not induce changes in unidirectional fluxes of Cl⁻ or Na⁺ or in the (I_sc) in either the anterior or posterior intestine.

     

Retinal development in the gilthead seabream Sparus aurata

The retinal development of the gilthead seabream Sparus aurata has been analysed from late embryonic development to juvenile stages using classical histological and immunohistological methods. Five significant phases were established. Phases 1 and 2 comprise the late embryonic and hatching stages, respectively. The results indicate that during these early stages the retina is composed of a single neuroblastic layer that consists of undifferentiated retinal progenitor cells. Phase 3 (late prolarval stage) is characterized by the emergence of the retinal layers and the appearance of neurochemical profiles in differentiating photoreceptors, amacrine and ganglion cells. Phases 4 and 5 comprise the late larval and juvenile stages. In these stages, all the retinal cell types can be detected immunohistochemically. All the maturational events described are first detected in the central retina and, as development progresses, spread to the rest of the retina following a central‐to‐peripheral gradient. The results of this study suggest that S. aurata is an altricial teleost species that hatches with a morphologically undifferentiated retina. The most relevant processes involved in retinogenesis occur during the late prolarval stage (phase 3).     

Intestinal glucose and galactose transport in the cultured gilthead bream (Sparus aurata)

1. Electrical parameters and transepithelial glucose and galactose transport were determined in vitro across anterior and posterior intestine of the culture fish Sparus aurata. 2. Electrical potential difference (PD) and short-circuit current (Isc) were serosa-positive in anterior intestine, while they were serosa-negative or near zero in posterior intestine. 3. Tissue conductance (Gt) was higher in posterior than in anterior intestine. In both parts it was decreased when the Na ion was omitted in mucosal and serosal reservoirs. 4. Addition of glucose or galactose to the mucosal side of intestine caused an increase in PD and Isc in posterior intestine but did not significantly change PD and Isc in anterior intestine. 5. Isotopic flux of glucose and galactose measurements in short-circuit conditions showed a net active glucose and galactose absorption in posterior intestine, while in anterior intestine active transport of glucose or galactose was not observed. 6. The net transport of glucose and galactose in posterior intestine was decreased to zero in the absence of Na in mucosal and serosal reservoirs or in the presence of ouabain (1 mM) in serosal solution.     

Genetic structure of gilthead seabream, Sparus aurata, in the Central Mediterranean Sea

The gilthead seabream, Sparus aurata, represents an important economic resource for Mediterranean aquaculture. In spite of its wide geographic distribution and economic importance, only recently studies have been carried out on the genetic composition of natural populations, which have revealed a picture of a heterogeneous degree of genetic differentiation among S. aurata populations. In this study an allozyme analysis of samples from six different collecting sites along the Italian and Croatian coasts was carried out, covering an area in the Central Mediterranean sea that has yet to be investigated through gene-enzyme systems. Data on 26 gene loci, 10 of which are polymorphic, indicate a slight but significant genetic structure (F_ST = 0.0167) of the species. A hierarchical analysis of population subdivision made it possible to identify three different assemblages found in the Adriatic Sea, Tyrrhenian Sea and Sardinian Channel, though an isolation by distance model can be rejected. The results are discussed in the light of previous literature and taking conservation into consideration.     

Hormonal mechanisms regulating hepatic vitellogenin synthesis in the gilthead sea bream,Sparus aurata

Experiments were carried out to study invitro the effects of 17-estradiol (E₂), homologouspituitary homogenate (HPH), and recombinant red sea bream growthhormone (sbGH) on vitellogenin (VTG) secretion from cultured sea breamliver fragments. Basal secretion of VTG was found to be significantlyhigher in the prespawning period, compared with sea bream liver in thespawning and postspawning periods. Similarly, the sea bream liverobtained during the prespawning period responded more significantly totreatments with E₂, HPH, or sbGH compared with sea breamliver during spawning. In the postspawning period, treatments withE₂, HPH, or sbGH were without significant effect on VTGsecretion level in sea bream liver. The level of E₂receptors was also analyzed by Western blot analysis. The resultdemonstrates a significantly higher level of E₂ receptors in the sea bream liver at the prespawning stage compared with those atthe spawning and postspawning stages. The findings support thehypothesis that homologous upregulation of estrogen receptors plays animportant role in the estrogen-sensitive control of VTG synthesis inthe sea bream liver.

     

Selected plasma biochemistry parameters in gilthead seabream (Sparus aurata) juveniles

The aim of this study was to assess plasma biochemistry parameters with the potential of being used as indicators of the nutritional status for healthy gilthead seabream juveniles. Triplicate groups of 18 seabream (body weight of 58 g) were kept unfed for 24 h, 7 or 14 days. Nine fish per treatment were then sampled randomly for blood collection and the following parameters analyzed in the plasma using standard clinical methods: glucose; protein; triglycerides; cholesterol; calcium; magnesium; inorganic phosphorus; alkaline phosphatase (ALP); aspartate aminotransferase (AST); lactate dehydrogenase (LDH); gamma‐glutamyl transferase (GGT); creatine phosphokinase (CPK); and lipase. Biochemical parameters showed lower variability among individuals than did enzymatic parameters. Plasma glucose, protein, cholesterol, calcium and inorganic phosphorus levels were inversely related to the duration of starvation. On the contrary, plasma triglycerides decreased significantly during the first week of starvation and remained stable in the second week. Plasma ALP, AST and LDH decreased significantly after 1 week of starvation and then remained constant. In healthy seabream juveniles, plasma glucose, protein, cholesterol, calcium and inorganic phosphorus are responsive to starvation and may be useful indicators of the nutritional status of the animals. Indicative baseline reference values for gilthead seabream juveniles starved for 24 h and held at optimum temperature are: protein, 3.7–4.9 g dl^?1; cholesterol, 341–407 mg dl^?1; calcium, 13.1–8.0 mg dl^?1; and inorganic phosphorus, 10–14.2 mg dl^?1. Plasma triglycerides, along with plasma enzyme activities, may be useful as indicators of short term starvation. For these parameters baseline values after 1 week of starvation were: triglycerides: 138–230 mg dl^?1; ALP: 58–125 U L^?1; AST: 15–127 U L^?1; and LDH 61–677 U L^?1. Plasma glucose is only responsive to longer starvation periods, remaining relatively stable during the first week of starvation, and ranging from 59 to 196 mg dl^?1.     

Gill area and dimensions of gilthead sea bream Sparus aurata L.

Detailed measurements of gill area and constituent variables (total filament length, lamellar frequency and bilateral area) were performed on both hemibranchs of all eight arches in six specimens of gilthead sea bream Sparus aurata (mean ±s.e . 49·9 ± 0·2 g). Shrinkage was also quantified and results were corrected accordingly. Filament number decreased from the first to the fourth gill arch, and average bilateral area of secondary lamellae was higher in the second and third arches. Total and mean filament length, total number of secondary lamellae and total gill area (A_TG) were lower in posterior than in anterior hemibranchs of the second, third and fourth gill arches; while the opposite was observed for the first arch. Lamellar frequency was increased in posterior hemibranchs of all arches compared to that in anterior hemibranchs, especially at the fourth arch. Comparison of the actually measured A_TG and constituent variables with estimates revealed that the third gill arch is the most representative for appropriate measurements and that any of its components (even one hemibranch) approximates the best A_TG (within the range of 0·2–4·3%, P > 0·05) and related dimensions. Consequently, necessary measurements were restricted to the posterior hemibranch of the third gill arch, and A_TG and dimensions (y) were estimated in 21 specimens (23·5–217·6 g) and correlated to body mass (M) according to the allometric equation y = aM^b. As fish increased in size, A_TG (b= 0·664), total (b= 0·425) and mean (b= 0·323) filament length, total number of filaments (b= 0·103) and secondary lamellae (b= 0·377), as well as average lamellar bilateral area (b= 0·288), increased, while the opposite was observed for lamellar frequency (b=?0·049) and mass‐specific area (b=?0·336). Data obtained are discussed in relation to S. aurata activity and living ethology.     

Influence of cortisol on osmoregulation and energy metabolism in gilthead seabream Sparus aurata

Gilthead seabream Sparus aurata were injected intraperitoneally with slow-release implants of coconut oil alone or containing cortisol (50 and 100 microg x g(-1) body weight), and sampled after two, five, and seven days to assess the simultaneous effects of cortisol on both osmoregulation and energy metabolism. Plasma cortisol levels increased in treated fish to 50-70 ng x ml(-1). An enhanced hypoosmoregulatory capacity of cortisol-implanted fish is suggested by the increase observed in gill Na+, K+-ATPase activity, and the decrease observed in plasma ion concentration (Na+ and Cl-) and osmolality. Cortisol also elicited metabolic changes in liver (increased gluconeogenic potential suggested by elevated FBPase activity, and decreased potential of glycolysis and pentose-phosphate shunt, suggested by the decreased activities of both PK and G6PDH) supporting changes in levels of plasma metabolites suitable for use in other tissues. Thus in this study, we demonstrate for the first time in fish that cortisol treatments elicit changes in the use of exogenous glucose in gills (decreased HK activity) and an increased glycolytic and glycogenic potential in brain (increased GPase, PK and PFK activities).     

Distribution of deformities among cultured Sparus aurata marketed in Istanbul,Turkey

Deformities/anomalies in fish body shapes have important implications on the marketability of the fish and thus can affect particularly the consumer perception of aquaculture-produced fish, raising concerns on animal welfare. The aim of this study was to detect the distribution of deformities in cultivated Sparus aurata that were raised to market size and sold in Istanbul Gürpınar Wholesale Fish Market in 2017–2018. We used external examination methods and X-ray imaging techniques to detect body deformities. Various types of deformities were found such as lordosis, cranial malformations, malpigmentation and change in the number of vertebrae. In most cases the same fish exhibited several malformations.     

Characterization of digestive carbohydrase activity in the gilthead seabream (Sparus aurata)

Six species of Phallodrilinae are reported from Hainan Island in southern China. The mesopsammic Aktedrilus yiboi sp. nov. is new to science. It is characterized by a combination of (1) small, straight, conical, strongly cuticularized penis sheaths, (2) posterior prostate glands being associated with the most ectal parts of the atria, and (3) small spermathecal ampulla. Bathydrilus ampliductus Erséus, 1997 is recorded for the first time since it was originally described from Australia's Northern Territory.     

Evaluation of gilthead sea bream, Sparus aurata, sperm quality after cryopreservation in 5 ml macrotubes

Cryopreservation produces several types of damage in spermatozoa, leading to fertility impairment. The reduction arises both from a lower viability post-thaw and from sublethal dysfunctions in some of the surviving cells. In the present study, we have analysed the effect of cryopreservation in 5 ml macrotubes on the quality of post-thawed gilthead sea bream sperm. Several standard sperm quality parameters were determined: pH and osmolarity of seminal plasma, sperm concentration, and motility. An exhaustive determination of sperm quality before and after cryopreservation was investigated. Several parameters related with spermatozoal status were determined: ATP content, plasma membrane integrity and functionality, mitochondrial functionality, and sperm fertility. Our results demonstrated that gilthead sea bream spermatozoa suffer several types of damage after freezing/thawing. The percentage of viable cells slightly decreased after cryopreservation, however plasma membrane was affected by cryopreservation, since cells could not resist the hyperosmotic shock. Mitochondrial status was affected by cryopreservation since there was a decrease in the parameters of sperm motility, ATP content (3.17 nmol ATP/10(5) spermatozoa to 1.7 nmol ATP/10(5) spermatozoa in 1:20 frozen samples) and an increase of the percentage of cells with mitochondrial depolarized membranes (11% for fresh and 27% for 1:20 frozen samples). Fertility rate was similar either using fresh or frozen/thawed sperm (77 and 75% hatched larvae, respectively).     

Induced swimming modified the antioxidant status of gilthead seabream (Sparus aurata)

Swimming has relevant physiological changes in farmed fish, although the potential link between swimming and oxidative stress remains poorly studied. We investigated the effects of different medium-term moderate swimming conditions for 6 h on the antioxidant status of gilthead seabream (Sparus aurata), analyzing the activity of enzymes related to oxidative stress in the liver and skeletal red and white muscle. Forty fish were induced to swim individually with the following conditions: steady low (SL, 0.8 body length (BL)·s⁻¹), steady high (SH, 2.3 BL·s⁻¹), oscillating low (OL, 0.2–0.8 BL·s⁻¹) and oscillating high (OH, 0.8–2.3 BL·s⁻¹) velocities, and a non-exercised group with minimal water flow (MF, < 0.1 BL·s⁻¹). All swimming conditions resulted in lower activities of superoxide dismutase (SOD), glutathione reductase (GR), and glutathione-S-transferase (GST) in the liver compared to the MF group, while steady swimming (SL and SH) led to higher reduced glutathione/oxidized glutathione ratio (GSH/GSSG) compared to the MF condition. Swimming also differently modulated the antioxidant enzyme activities in red and white muscles. The OH condition increased lipid peroxidation (LPO), catalase (CAT) and glutathione peroxidase (GPx) activities in the red muscle, decreasing the GSH/GSSG ratio, whereas the SL condition led to increased GSH. Oscillating swimming conditions (OL and OH) led to lower CAT activity in the white muscle, although GPx activity was increased. The GSH/GSSG ratio in white muscle was increased in all swimming conditions. Liver and skeletal muscle antioxidant status was modulated by exercise, highlighting the importance of adequate swimming conditions to minimize oxidative stress in gilthead seabream.     

Radiological characterization of gilthead seabream (Sparus aurata) by X-ray computed tomography

In recent years, the increasing use of fish as new animal models in scientific research and the growth of fish farming (mainly for human consumption) have highlighted the need for advanced technology to deepen our knowledge of fish biology. Hence, the present study was carried out to radiologically analyse the whole body of gilthead seabream (Sparus aurata) specimens using X-ray computed tomography (CT). Images were acquired in an Albira SPECT/PET/CT tri-modal preclinical-scanner. Segmentation, measurements and three-dimensional reconstruction were made using the Carestream Molecular imaging Albira CT system in conjunction with Pmod, AMIDE and Amira software packages. The results showed that the density values of gilthead seabream are in the range −700 to +2500 HU for the whole body. We also determined the density ranges that topographically coincide with the swim bladder, soft tissues, fat, skin and skeleton. This work describes, validates and demonstrates the application of a fully automated image analysis technique to study and quantify fish body composition, whether segmented or as a whole. In addition, the basis for applying this image technique in other in vivo studies is established.     

Water temperature affects osmoregulatory responses in gilthead sea bream (Sparus aurata L.)

Sea bream (Sparus aurata Linneaus) was acclimated to three salinity concentrations, viz. 5 (LSW), 38 (SW) and 55psμ (HSW) and three water temperatures regimes (12, 19 and 26 °C) for five weeks. Osmoregulatory capacity parameters (plasma osmolality, sodium, chloride, cortisol, and branchial and renal Na⁺,K⁺-ATPase activities) were also assessed. Salinity and temperature affected all of the parameters tested. Our results indicate that environmental temperature modulates capacity in sea bream, independent of environmental salinity, and set points of plasma osmolality and ion concentrations depend on both ambient salinity and temperature. Acclimation to extreme salinity resulted in stress, indicated by elevated basal plasma cortisol levels. Response to salinity was affected by ambient temperature. A comparison between branchial and renal Na⁺,K⁺-ATPase activities appears instrumental in explaining salinity and temperature responses. Sea bream regulate branchial enzyme copy numbers (V_max) in hyperosmotic media (SW and HSW) to deal with ambient temperature effects on activity; combinations of high temperatures and salinity may exceed the adaptive capacity of sea bream. Salinity compromises the branchial enzyme capacity (compared to basal activity at a set salinity) when temperature is elevated and the scope for temperature adaptation becomes smaller at increasing salinity. Renal Na⁺,K⁺-ATPase capacity appears fixed and activity appears to be determined by temperature.     

Ontogenesis of opercular deformities in gilthead sea bream Sparus aurata: a histological description

The aim of this study was to characterize histological changes during opercular osteogenesis in farmed gilthead sea bream Sparus aurata larvae from 7 to 69 days post hatching (dph) and compare normal osteogenesis with that of deformed opercles. Mild opercular deformities were first detected in 19 dph larvae by folding of the opercle's distal edge into the gill chamber. Here, the variation in the phenotype and the irregular bone structure at the curled part of the opercles is described and compared with the histology of normal opercles. Results indicated that deformed opercles still undergo bone growth with the addition of new matrix by osteoblasts at the opercular surface, especially at its edges. No significant difference was found in bone thickness between deformed and normal opercles. In addition to differences in bone architecture, differences in collagen fibre thickness between normal and deformed opercles were also found.     

Quantitative trait loci affecting morphology traits in gilthead seabream (Sparus aurata L.)

We report a quantitative trait loci (QTL) mapping study on 18 morphometric characters in gilthead seabream based on a total of 74 informative microsatellite markers genotyped in 409 offspring coming from 10 paternal half‐sib families. Statistical analysis was carried out using a linear regression approach, and various suggestive and significant morphology QTL were detected in three (9, 21 and 25) of nine linkage groups examined. Fitting body weight as a covariate reduced the significance of some QTL but revealed three new QTL in other linkage groups (LG6 and LG10). Current results combined with those obtained from previous studies underline highly significant loci affecting overall growth and morphology in S. aurata.     

Cytochemical characterization of leucocytes from the seawater teleost,gilthead seabream (Sparus aurata L.)

The cytochemical characterization of head-kidney and peripheral blood leucocytes of gilthead seabream (Sparus aurata L.) was studied by light and electron microscopy. Neutrophilic granulocytes show some cytoplasmic granules, which are positive for alkaline phosphatase and peroxidase but acid phosphatase negative. The scarce granules found in the cytoplasm of the circulating neutrophils and their cytochemical features seem to be indicative of an immature stage. Acidophils are also alkaline phosphatase and peroxidase positive at pH 11.0. They are strongly positive for acid phosphatase and acid phosphatase activity may thus be considered a cytochemical marker to characterize and differentiate neutrophilic from acidophilic granulocytes in this fish species. Three granule populations are characterized in the cytoplasm of the gilthead seabream acidophils: the first is positive only for peroxidase and the second contains a dense core with acid and alkaline phosphatase activities, surrounded by a thin peroxidase positive electron-dense halo. The third granule type contains an eccentric core, which is strongly positive for acid and alkaline phosphatase and peroxidase. As regards their cytochemical features, the first and second granule types seem to correspond respectively to the azurophilic and specific granules found in acidophils of mammals and could be involved in phagocytic processes, thus playing an important microbicidal role in this species. The monocytes, monocyte-macrophages and macrophages show different cytochemical features. The first have scarce acid phosphatase-positive lysosomes, while blood monocyte-macrophages and macrophages are positive for acid and alkaline phosphatases and for peroxidase; the monocyte-macrophages show scarce lysosomes.