Effect of two sulfur-containing amino acids, taurine and hypotaurine in European sea bass (Dicentrarchus labrax) sperm cryopreservation.

In the present work, taurine and hypotaurine were evaluated as potential additives to improve European sea bass (Dicentrarchus labrax) sperm quality after cryopreservation. For cryopreservation, three different extenders were used: control extender (NAM), supplemented with 1mM taurine or supplemented with 1mM hypotaurine, all of them containing 10% Me2SO as cryoprotectant. To evaluate sperm quality of fresh and thawed sperm, motility (CASA: computer assisted sperm analysis), viability (SYBR Green/propidium iodide), lipid peroxidation (malondialdehyde level), protein oxidation (carbonyl content), glutathione peroxidase, glutathione reductase and superoxide dismutase activities and DNA fragmentation (comet assay) were quantified. The result demonstrated that 1 mM hypotaurine supplemented extender increased total motility (30.1 ± 3.2%), and that 1 mM taurine extender produced higher velocity (18.1 ± 2.6 µm/s) and linearity (46.0 ± 4.8%) than the control extender (21.8 ± 3.2%, 15.5 ± 1.3 µm/s, 41.8 ± 2.4%, respectively). Cell viability, lipid peroxidation and protein oxidation were not statistically different between treatments. Similar results were obtained for glutathione peroxidase and superoxide dismutase activities. Only glutathione reductase showed differential activity before and after freezing, increasing its activity in thawed sperm. Regarding the comet assay results, taurine and hypotaurine significantly reduced DNA fragmentation (52.8 ± 0.9% and 51.8 ± 0.9%, respectively) in comparison to the control (55.7 ± 0.8%). In conclusion, for European sea bass sperm cryopreservation, extenders supplemented with 1 mM taurine and 1 mM hypotaurine improved some parameters of sperm quality after thawing, resulting in better motility and lower DNA damage than the control, two very important factors related to fertilization success.

Sea bass sperm freezability is influenced by motility variables and membrane lipid composition but not by membrane integrity and lipid peroxidation.

Cryopreserved sperm quality depends on the characteristics of fresh sperm. Thus, it is necessary to establish a group of variables to predict the cryopreservation potential of the fresh samples with the aim of optimizing resources. Motility, viability, lipid peroxidation and lipid profile of European sea bass (Dicentrarchus labrax) sperm were determined before and after cryopreservation to establish which variables more accurately predict the sperm cryopreservation potential in this species. Cryopreservation compromised sperm quality, expressed as a reduction of motility (46.5 ± 2.0% to 35.3 ± 2.5%; P<0.01) and viability (91.3 ± 0.7% to 69.9 ± 1.6%; P<0.01), and produced an increase in lipid peroxidation (2.4 ± 0.4 to 4.0 ± 0.4 µmoles MDA/mill spz; P<0.01). Also, significant changes were observed in the lipid composition before and after freezing, resulting in a reduction in the cholesterol/phospholipids ratio (1.4 ± 0.1 to 1.1 ± 0.0; P<0.01), phosphatidylcholine (47.7 ± 0.8% to 44.2 ± 0.8%; P<0.01) and oleic acid (8.7 ± 0.2% to 8.3 ± 0.2%; P<0.05) in cryopreserved sperm, as well as an increase in lysophosphatidylcholine (4.4 ± 0.3% to 4.8 ± 0.3%; P<0.01) and C24:1n9 fatty acid (0.5 ± 0.1% to 0.6 ± 0.1%; P<0.05). Motility, velocity, cholesterol/phospholipids ratio, monounsaturated fatty acids and the n3/n6 ratio were positively correlated (P<0.05) before and after freezing, whereas, viability and lipid peroxidation were not correlated. Motility and the cholesterol/phospholipids (CHO/PL) ratio were negatively correlated (P<0.05) with each other and the CHO/PL ratio was positively correlated (P<0.05) with lipid peroxidation. Therefore, the results demonstrated that motility and plasma membrane lipid composition (CHO/PL) were the most desirable variables determined in fresh samples to predict cryo-resistance in European sea bass sperm, taking into account the effect of both on cryopreserved sperm quality.

Incorporation of ascorbic acid and α-tocopherol to the extender media to enhance antioxidant system of cryopreserved sea bass sperm.

Despite the overwhelming application of sperm cryopreservation in aquaculture and broodstock management, its detrimental effects on sperm quality must be taken into account. Imbalance of reactive oxygen species is considered one of the main triggers of cell damage after cryopreservation, because the spermatozoa antioxidant system is decimated during this process, mainly because the natural antioxidants present in seminal plasma diminish when sperm is diluted in extenders. It has been demonstrated that the addition of antioxidants to the extender improves the quality of thawed sperm. Thus, the aim of the present work was to evaluate the status of the antioxidant system in cryopreserved sea bass sperm, and the possibility of enhancing this system to reduce oxidation of the membrane compounds by extender supplementation with vitamins. To do this, sperm from European sea bass (Dicentrarchus labrax) was cryopreserved using an extender control (NAM), supplemented with 0.1 mm α-tocopherol or 0.1 mm ascorbic acid. Sperm motility (computer assisted sperm analysis (CASA) parameters), viability (SYBR Green/propidium iodide (PI)), lipid peroxidation (malondialdehyde (MDA) levels) and protein oxidation (DNPH levels) were analyzed, as well as the status of the sperm antioxidant system by determining glutathione peroxidase, glutathione reductase and superoxide dismutase (GPX, GSR and SOD) activity. The results demonstrated that extenders containing vitamins significantly increased sperm motility. Total motility, velocity and linearity increased from 31.2 ± 3.0 µm/sec, 18.3 ± 1.7 µm/sec and 46.9 ± 2.0% in extender containing 0.1 mm α-tocopherol or 30.6 ± 3.9 µm/sec, 19.5 ± 1.6 µm/sec and 47.9 ± 2.2% in extender containing 1 mm ascorbic acid respect to the extender control (20.7 ± 3.3 µm/sec, 13.8 ± 1.7 µm/sec and 37.3 ± 4.1%). However, viability and levels of lipid peroxidation and protein oxidation were not affected by the presence of these antioxidants, suggesting that membrane impairment could be more associated to osmotic shock or membrane destabilization than oxidative damage. The increased activity of both GPX and GSR after cryopreservation showed that the antioxidant system of sea bass sperm must play an important role in preventing oxidation of the membrane compounds. In conclusion, the addition of α-tocopherol and ascorbic acid to the extender media, together with the antioxidant system of the spermatozoa improved sea bass sperm motility, which is one of the impairment parameters most affected by cryopreservation.

Iodine and selenium supplementation increased survival and changed thyroid hormone status in Senegalese sole (Solea senegalensis) larvae reared in a recirculation system.

To test how iodine and both iodine and selenium supplementation affected the thyroid status as well as growth and survival in Senegalese sole, larvae were reared in a recirculation system from 15 to 34 DAH. Sets of three tanks were assigned to each of the following three diets: control (C), iodine (I) and iodine and selenium (I + Se). Samples were collected at 15, 27 and 34 DAH to determine dry weight, iodine and selenium levels, GPx and ORD activities, thyroid hormone levels and thyroid follicles histology. At 34 DAH, fish from the control (C) treatment suffered from hyperplasia of the thyroid follicles (goitre), whereas iodine-treated larvae did not (I and I + Se). Lower survival rates in the C groups were probably a consequence of the hyperplasia. Moreover, there was an improvement in thyroid hormone status in I- and I + Se-treated larvae, showing that further supplementation of live feed with iodine can be crucial for fish at early life stages, as it seems to sustain normal larval development, when reared in a recirculation system. Selenium did not affect the results. Together with previous results, this indicates selenium supplement is more important at younger life stages.

Changes in Solea senegalensis sperm quality throughout the year.

Some of the Senegalese sole (Solea senegalensis) broodstock reproductive constraints are related to sperm quality. Although they present two defined spawning season (spring and autumn), males gave semen during all the year thus an exhaustive annual sperm analysis is important to determine the seasonal changes in semen quality. Sampling was performed monthly during one year, analyzing different cellular parameters to better understand sperm quality limitations obstructing sole mass production. The percentage of progressive motile cells and their linear velocity showed a decrease from March (beginning of the first spawning season) to July (when the highest temperatures were observed), followed by a slight increase in August and October (second spawning season). DNA fragmentation values showed highest values between the two spawning seasons and decreased to the end of the year. The percentage of apoptotic cells was lowest in March (beginning of the first spawning season) and the highest in November. The percentage of cells resistant to seawater exposure presented two peaks related with both spawning seasons. There was a tendency for the semen to attain a quality peak between the beginning and the middle of the first spawning season (March-May), followed by a pronounced decrease, achieving the lowest values during the months with the highest temperature. Also, the different males present in the broodstocks reach their sperm quality peak at different times, which will result in an unequal contribution for the next generation.

The influence of certain aminoacids and vitamins on post-thaw fish sperm motility, viability and DNA fragmentation.

During cryopreservation, dilution in the extender media reduces the seminal plasma constituents being cells more vulnerable to oxidative stress. Vitamins (C and E) and the amino acids taurine and hypotaurine are powerful antioxidants naturally present in seminal plasma. Whether their effect may improve sperm quality and reduce sperm DNA damage after cryopreservation in fish sperm still remains unclear. Thus, the aim of the present work was to analyse the effect of extender supplementation with several antioxidant components on post-thawed sperm motility, viability and DNA integrity of two commercial species, gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax). Sperm collected from ten to twelve individuals was cryopreserved in ten different extenders containing: taurine and hypotaurine (1 and 10mM), ascorbic acid (1 and 10mM), α-tocoferol (0.1 and 0.5 mM) or 1 ml/l of a commercial cell antioxidant supplement. Cell viability, motility and DNA fragmentation were determined in post-thawed samples. Addition of antioxidants (vitamins and amino acids) to D. labrax and S. aurata extenders did not significantly increase the parameters of motility (TM, PM, VCL, VSL and Lin) or viability, although 1mM taurine slightly increased the percentage of motile cells (TM) in S. aurata. DNA fragmentation (DNA in tail and Olive tail moment) in D. labrax sperm was higher in treatments containing vitamins than amino acids or control. However in S. aurata sperm, antioxidants especially taurine and hypotaurine, significantly reduced both DNA fragmentation parameters, protecting DNA against strand breaks. These results suggest a species-specific effect depending on the type of antioxidants used.

Endocrine and milt response of Senegalese sole, Solea senegalensis, males maintained in captivity.

Improving fertilization success in captive Senegalese sole broodstocks has been a challenge in the last years. Recent reports suggest that low sperm volume and quality could be one of the reasons leading to poor fertilization rates, although further studies are needed to reach a conclusive explanation. Here, we report on several experiments focused on this issue. Seasonal profiles of plasma androgen levels (testosterone and 11-ketotestosterone) and sperm production and quality parameters were assessed, although no statistical correlations among them were identified. The response of males to female presence/absence was also analyzed. Long-term isolation from females decreased male androgen levels at the peak of the reproductive period, suggesting some kind of disrupting effects on the endocrine system. On the other hand, short-term exposure of previously isolated males to ripe females decreased androgen levels, possibly reflecting a rapid steroidogenic shift promoting final maturation of spermatozoa, and increased sperm viability, motility and velocity, thus, supporting the concept of positive effects of female contact on male sole performance. Further evidence sustaining the relevant female-to-male communication in sole reproduction was obtained after treating the females with progestagen 17α,20ß-dihydroxy-4-pregnen-3-one (regarded as pre-ovulatory pheromone in fish) and registering a significant increase in sperm viability, velocity and motility in surrounding males. Finally, we found that a single administration of a 20 µg/kg GnRH analogue in males was effective in stimulating androgen release and sperm quality, although the effects were transient and thus, the use of sustained hormone delivery methods were suggested for improving efficiency. Our results point to velocity, viability, and motility as the most sensitive parameters in sole sperm, although further studies will have to evaluate whether these parameters have any relation with fertilization success in captive broodstocks of this important aquaculture species.

Sperm quality evaluation in Solea senegalensis during the reproductive season at cellular level.

Sperm quality seems to be one of the reasons for the reproduction constraints faced by Senegalese sole (Solea senegalensis) aquaculturists. Previous studies in this species indicated that the sperm quality of individuals kept in culture varies throughout the year and that different sperm subpopulations can be identified in ejaculates according to the motility pattern of spermatozoa. Aiming to better understand factors affecting sole sperm quality in captivity, sperm of 11 males was assessed during the reproductive season using different parameters: motility characteristics using CASA analysis; cell plasma membrane resistance to seawater hyperosmolarity; DNA fragmentation with single-cell gel electrophoresis; and early apoptosis, labeled with Annexin-V FITC. Computer-assisted sperm analyses motility data were treated using multivariate analysis to identify the presence of different spermatozoa subpopulations according to their motility pattern. Four distinct sperm subpopulations were obtained: Subpop1, which includes fast linear spermatozoa; Subpop2, made up of fast nonlinear spermatozoa; Subpop3, which includes slow linear spermatozoa; and Subpop4, which contains slow nonlinear spermatozoa. The sperm subpopulation structure varied with time after activation and with male. Low cell resistance to the seawater hyperosmotic conditions was noticed. The Annexin-V assay allowed the identification of an apoptotic population ranging from 6% to 20%. A high percentage of cells (64.1%) showed a DNA fragmentation level below 30%, but these values varied significantly between males. DNA fragmentation appears to be related to cell membrane resistance to hyperosmotic conditions faced by the cells when in contact with seawater. This condition seems to modulate the composition of the motile sperm population and performance after activation. This phenomenon could be related to the spermatozoa maturation process.

Lunar and daily spawning rhythms of Senegal sole Solea senegalensis.

A periodicity of 29 days was observed in spawning rhythms in Senegal sole Solea senegalensis, with an acrophase around the last quarter and the new moon. In both spring and autumn, a very marked nocturnal spawning rhythm was registered, with spawning beginning after dusk and the acrophase occurring around 2300 hours. When the photoperiod was artificially extended (from 10L:14D to 14L:10D), S. senegalensis synchronized to the new photoperiod: spawning took place after the new 'dusk', the beginning gradually shifting from 2100 to 2300 hours and the acrophase from 2325 to 0032 hours. Under continuous light conditions, fish sustained rhythmicity for 2 days, with an acrophase at 2249 hours, which suggested the existence of an endogenous pacemaker controlling the daily spawning rhythm. These findings provided new insights for better understanding the reproductive physiology of this species and for optimizing the timing protocols of egg collection and larvae production in S. senegalensis aquaculture.

Metabolism of tryptophan, methionine and arginine in Diplodus sargus larvae fed rotifers: effect of amino acid supplementation.

Dietary amino acids imbalances have been described when fish larvae are fed rotifers, what may lead to a reduction in growth rate. The tube-feeding technique can be used to assess the effect of free amino acid short term supplementation. In this study supplementation of tryptophan, methionine and arginine were tested in Diplodus sargus. Single crystalline (14)C amino acids as well as a mix of (14)C amino acids were used as tracers to compare results of individual amino acids metabolism with the average of all amino acids. The results show low absorption efficiencies for tryptophan (70%) and arginine (80%) and similar absorption for methionine (90%) when compared with the average of all amino acids. Supplementation of these amino acids seems to be viable but it did not result in higher retention compared to the amino acid mix. This means that tryptophan, methionine and arginine are probably not the limiting amino acid when Diplodus sargus larvae are fed rotifers. However, supplementation in these IAA may be required for their roles as precursors of important molecules other than proteins, in order to improve larval quality and/or performance.

Stress response and changes in amino acid requirements in Senegalese sole (Solea senegalensis Kaup 1858).

Fish in aquaculture are often exposed to various stressors that may change their ability to survive or limit growth. Amino acids are used for processes other than growth, including stress response. This study intended to analyse how repeated acute handling stress can affect growth and amino acid requirements in fish. Senegalese sole juveniles were weekly held in the air during 3 min (Handling) for 9 weeks; Control groups were left undisturbed. Growth and plasma levels of stress indicators and of free amino acids were assessed at the end of the experiment. Plasma cortisol and osmolality levels showed that fish in the Handling treatment were stressed, but growth was unaffected. Plasma amino acid concentrations indicate that their requirements in stressed fish were altered, which probably reflects the synthesis of proteins or other specific compounds related to stress response.

Dietary neutral lipid level and source in Senegalese sole (Solea senegalensis) larvae: effect on growth, lipid metabolism and digestive capacity.

Contrary to larval essential fatty acid (EFA) requirements, the effect of dietary neutral lipid supply has been little investigated in marine fish larvae. The present work investigates the effect of feeding Senegalese sole larvae on Artemia enriched with higher or lower doses of lipid emulsion. Two lipid sources - soybean oil and fish oil - were compared. From 16 days after hatching (DAH) onwards, larvae were fed one of four experimental treatments: Artemia enriched on a high or low dose of soybean oil emulsion (HS and LS) or Artemia enriched on a high or low dose of fish oil emulsion (HF and LF). In terms of growth, the dietary lipid level did not have a significant effect while the soybean oil treatments induced a lower growth than the fish oil-enriched Artemia. The fatty acid (FA) composition of the larvae closely reflected the dietary quantitative and qualitative FA profile. Only slight dietary effects were noted in the activity of trypsin, lipase and alkaline phosphatase. A higher amount of lipid droplets was noticeable in the posterior intestine epithelia and in the hepatocytes of larvae fed Artemia enriched with higher lipid doses, while LS-Artemia induced the lower lipid accumulation on the basal zone of the enterocytes, in accordance with the lowest total lipid level measured in this treatment. These results suggest an important effect of dietary total lipid level on lipid accumulation in the enterocytes and on FA absorption. At 33 DAH a tube feeding trial was conducted with 14C-labelled oleic acid (OA) or triolein (TRI), showing that the lower accumulation of lipid droplets in the larvae fed LS was associated with a significantly higher absorption and retention in the gut and body tissues of the TRI label. For OA no significant differences between treatments were found. TRI label was considerably more evacuated than OA, indicating that sole larvae may have a lower capacity to incorporate a triacylglycerol, which needs to be digested. Finally, OA appears to be preferentially utilized for energy production, accumulating more in larval tissues when absorbed in higher amounts.

Evaluation of candidate probiotic strains for gilthead sea bream larvae (Sparus aurata) using an in vivo approach.

AIMS: The aim of this study was to evaluate the effect of six bacterial strains on gilthead sea bream larvae (Sparus aurata). METHODS AND RESULTS: Six bacterial strains isolated from well-performing live food cultures were identified by sequencing fragments of their 16s rDNA genome to the genus level as Cytophaga sp., Roseobacter sp., Ruergeria sp., Paracoccus sp., Aeromonas sp. and Shewanella sp. Survival rates of gilthead sea bream larvae transferred to seawater added these bacterial strains at concentrations of 6 +/- 0.3 x 10(5) bacteria ml(-1) were similar to those of larvae transferred to sterilized seawater and showed an average of 86% at 9 days after hatching, whereas, survival rates of larvae transferred to filtered seawater were lower (P < 0.05), and showed an average of 39%, 9 days after hatching. CONCLUSION: Several bacterial strains isolated from well-performing live food cultures showed a positive effect for sea bream larvae when compared with filtered seawater. SIGNIFICANCE AND IMPACT OF THE STUDY: The approach used in this study could be applied as an in vivo evaluation method of candidate probiotic strains used in the rearing of marine fish larvae.

Dietary TAG source and level affect performance and lipase expression in larval sea bass (Dicentrarchus labrax).

The influence of dietary TAG source (fish oil, triolein, and coconut oil) and level (7.5 and 15% of the diet) on growth, lipase activity, and mRNA level was studied in sea bass larvae, from mouth opening until day 24 and from day 37 to 52. Fish oil and triolein induced better growth in both experiments, this being significant at a higher dietary level. Coconut oil significantly decreased growth at the higher level, possibly as the result of an excessive supply of medium-chain TAG. Growth was not related to lipase specific activity, suggesting a production in excess to dietary needs. Body lipid content was positively related to dietary lipid level and was affected by lipid quality. In addition, larval FA composition generally reflected that of the diet. The source of dietary lipid, but not the quantity, was shown to affect lipase activity significantly. Coconut oil diets induced the highest lipase activity, whereas the effect of fish oil was age dependent-it was similar to coconut oil at day 24 but induced the lowest lipase activity in 52-d-old larvae. The differential lipase response was probably caused by differences in the FA composition of the diet, related to the specificity of lipase toward FA differing in chain length and degree of saturation. No significant differences were found in lipase/glyceraldehyde-3-phosphate dehydrogenase mRNA, which suggests the existence of a posttranscriptional regulation mechanism.

Assimilation and catabolism of dispensable and indispensable free amino acids in post-larval Senegal sole (Solea senegalensis).

The postprandial metabolism of dietary free amino acids (AA) was studied in post-larval Senegal sole, Solea senegalensis, aged 32 days after hatching (DAH). The diet was administered as a single pulse (36 nl, 43.1 mmol/l) using a micro tube-feeding technique and a dissolved mixture of crystalline AA. In four separate treatments the diet contained L [U-(14)C] tracer for two indispensable AA (IAA), lysine and arginine or two dispensable amino acids (DAA), glutamate and alanine. The post-larva absorbed all tested AA from the diet with similar efficiency (97.5%). A small fraction of the IAA was catabolised (11.5+/-1.1 and 15.1+/-3.3%, for lysine and arginine, respectively) and a high proportion was retained in the body (86.7+/-1.3 and 81.6+/-4.1%). For the DAA more were catabolised (64.9+/-5.3% and 41.4+/-7.2% for glutamate and alanine, respectively) and less were retained (32.9+/-5.1% and 56.3+/-7.2%). On this basis, it appears that post-larval Senegal sole use DAA in preference to IAA as energy substrates while the retention (assimilation efficiency) is better for the IAA. These results support other recent studies that early stages of fish have a better capacity to regulate AA catabolism than previously believed and that indispensable AA are saved for body growth.

Glyconjugates in epidermal, branchial and digestive mucous cells and gastric glands of gilthead sea bream, Sparus aurata, Senegal sole, Solea senegalensis and Siberian sturgeon, Acipenser baeri development.

Epidermal, branchial and digestive mucous cells, and the gastric glands of larvae/postlarvae (from hatching until 45 days posthatching) of three fish species (two teleostean and a chondrostean) were investigated using conventional histochemical methods (periodic acid schiff -PAS-, diastase-PAS; alcian blue pH 0.5, 1 and 2.5) in order to distinguish neutral and acidic (carboxylated and sulphated) glycoconjugates, as well as bromophenol blue reaction for identification of proteins. Additionally, the presence and distribution of sugar residues in the oligosaccharide side chains of glycoconjugates were investigated using horseradish peroxidase (HPR)-conjugated lectins (Con A, DBA, WGA and UEA-I). Most mucous cells (digestive, epidermal and branchial) of Siberian sturgeon, Acipenser baeri, sea bream, Sparus aurata and Senegal sole, Solea senegalensis larvae were PAS- and alcian blue- (pH 2.5 and 0.5) positive, with small variations between organs/tissues and species. Bromophenol blue reaction (general proteins) was positive in a minority of the mucous cells, usually in those cells which were PAS-negative. Proteins rich in sulphydryl (-SH) and/or disulphide (-S-S-) groups related with the glycoprotein nature of the glycoconjugates present in mucous cells were also observed. Epidermal, branchial and digestive mucous cells of all studied larvae did not contain glycogen or lipids. Con A lectin staining was negative in all mucous cells types of sea bream and sole, but oesophageal mucous cell of sturgeon were reactive to different lectin reactions, suggesting the presence of mannose -Man- and/or glucose -Glc-, L-fucose -Fuc- ; N-acetyl-D-galactosamine -GalNAc-, as well as N-acetyl-D-glucosamine- GlcNAc - and/or sialic acid -NANA- residues. Digestive mucous cells of all studied larvae were positive to WGA and DBA lectins. Epidermal and branchial mucous cells of sea bream and sole were Con A, DBA and UEA-I unreactive. However, mucous cells of sturgeon larvae were stained with UEA-I lectin. Gastric glands appear very early in sturgeon stomach larvae development (between 5-6 days posthatching) but rather late (around 40 days) during the ontogeny of sole and sea bream larvae. These glands contain neutral glycoproteins with Man and/or Glc, Fuc, GlcNAc- and/or sialic acid and rich in GalNAc- sugar residues, as well as proteins moderately rich in arginine, and others particularly rich in tyrosine and tryptophan.

Free amino acids are absorbed faster and assimilated more efficiently than protein in postlarval Senegal sole (Solea senegalensis).

To improve the formulation of diets for the early stages of marine fish, assimilation rates of free amino acids (FAA) and protein in postlarval Senegal sole (Solea senegalensis) were determined. Fish (2.45 +/- 0.87 mg dry weight) were tube fed 36 nL of a diet of FAA containing L-[(35)S] methionine (FAA diet) or bovine serum albumin, containing L-[methylated-(14)C]bovine serum albumin (Prot-diet), both at a concentration of 4.08 g/L. A time series was performed, and the amounts of label in incubation water, liver, gut and body carcass were quantified. The FAA diet was absorbed with a 3.5-times-higher transfer rate (P < 0.001) from the gut into the larval body tissues compared with the Prot-diet. The FAA diet also was assimilated with greater efficiency than the Prot-diet (80% versus 58%, P: = 0.001). If we assume that the label present in the gut represents amino acids incorporated into the intestinal tissue, the assimilation efficiencies for the two diets were 89 and 64%. Therefore, FAA seems to be superior to protein as a dietary source of amino acids in Senegal sole postlarvae. However, because the absorption dynamics of protein and FAA differ, care should be taken when using the sources together to avoid amino acid imbalance.

Histomorphological and histochemical characteristics of the intestine of the Senegal sole, Solea senegalensis.

The Senegal sole, Solea senegalensis has been exploited extensively in aquaculture from different countries; at present an intensive production of larvae and adults is being achieved with some nutritional problems. Since this species displays very different life styles and feeding habits at different stages of its life history (larvae, metamorphosis, adults), and because digestive mucins are implicated in different physiological processes including: increase of digestive efficiency, promotion of macromolecules-absorption, buffering of intestinal fluid, prevention of proteolytic damage to the epithelium and defence against bacteria, etc., we studied the histomorphological aspects, as well as the histochemical distribution of carbohydrates, (PAS, Alcian Blue), proteins (Bromophenol Blue), lipids (Oil Red O, Black Sudan B) and glycoproteins (Horseradish peroxidase-conjugated lectins) in the intestinal epithelium of adult Solea senegalensis specimens. Our data are compared with those obtained in larvae and adults of this and other fish species. Primary and secondary folds, microvilli of the intestinal enterocytes, as well as mucous or goblet cells were observed with a scanning electron microscope. Enterocytes and mucocytes of the intestine of adult Solea senegalensis were characterized by a rich supply of sugar and oligosaccharides. Carbohydrates (glycogen and mucins), proteins and lipids were present in cytoplasm and microvilli--brush border--of the enterocytes, which contain GalNAc, GlcNAc, Man, Glc and sialic acid-N-acetyl-D-galactosamine glycoconjugates. Intestinal mucous cells were strongly or weakly stained with Alcian Blue (pH 2.5 and 1). PAS reactivity was intense in numerous goblet cells, but some cells were PAS unreactive or weakly stained. Some goblet cells were positive for Bromophenol Blue but numerous cells were unstained; thus many proteins and possibly lipids may be conjugated with sugars. A similar reactivity to WGA and to neuraminidase-WGA was identified in some intestinal goblet, which were Con A unreactive, indicating the absence of Man and/or Glc and NANA glycoconjugates. GalNAc residues were only scarcely present in glycoproteins of some goblet cells.

Immunocytochemical distribution of cytochrome P4501A (CYP1A) in developing gilthead seabream, Sparus aurata.

CYP1A is a major inducible enzyme in the metabolism of xenobiotic substrates. In this paper we investigate by means of immunohistochemistry, the tissue distribution of constitutive cytochrome P4501A (CYP1A) during the period of endogenous nutrition (from hatching until day 4) in developing gilthead seabream, Sparus aurata larvae. For this purpose, a polyclonal antiserum (BN-1, Biosense Laboratories) directed against conserved piscine CYP1A sequences was used on paraffin-embedded sections from seabream larvae. From hatching onward, CYP1A immunoreactivity was observed in the following tissues and cells: syncytial, oil-globule envelopes and matrix of the yolk-sac, kidney (epithelia of renal tubules), cardiac muscle cells, skin epidermal cells, troncal musculature, enterocytes of different intestinal regions, goblet cells of the bucco-pharyngeal region, gill epithelial cells and the endothelia of the vascular system of various tissues (especially from liver and brain). Moreover, eye (retina), olfactory epithelium and some positive nerve fibers located in the proximity of the olfactory bulbs and running ventrally toward the posterior brain were strongly CYP1A immunoreactive. In general, the intensity of immunostaining increased with larval development.