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Climate change is reshaping our planet.Warming surface waters, acidification, and deoxygenation are the most critical effects of climate change in aquatic environments. Increasing mean water temperatures modify species distribution, alters their basal metabolic rates, the occurrence and intensity of marine diseases, and the timing of pivotal biological events, among others. Ocean acidification results in physiological stress and inhibits the growth and calcification of endo- and exo-skeletons, while ocean deoxygenation, and particularly hypoxic events, may alter the distribution, aerobic scope, and survival of organisms (Reid et al., 2019). As climate change is projected to continue over this century and beyond, it is expected that the above-mentioned stressors will be intensified, further altering the structure, and functioning of marine ecosystems (Benedetti et al., 2021). Understanding and predicting the effects of climate change is one of the most pressing challenges in marine science, since this knowledge has an impact on fisheries, aquaculture, conservation, and applied ecology. Under this scenario, this Research Topic was conceived for updating and increasing the knowledge of ocean water rise on the biology and physiology of aquatic species, resulting in a Research Topic of four works on crustaceans, fish, and phytoplankton.

Gilthead seabream (Sparus aurata) tend to increase fat deposition during summer farming conditions in the Mediterranean, which may negatively affect productive performance and consumers' quality perception of the final product. Therefore, this study evaluated the impacts of protein to lipid ratios in low fishmeal/fish oil diets on growth performance, body composition, feed conversion and nutrient utilization of seabream on-grown during summer temperature conditions. The experimental diets contained low levels of fishmeal, fish oil, and crude protein (39%), differing in crude lipid content: 16% (MF diet) or 12% (LF diet). A growth trial was per-formed with seabream (initial weight: 100 & PLUSMN; 7 g) from August to October (water temperature: 23.1 & PLUSMN; 2.2 & DEG;C). A digestibility trial was also performed (at 23 & DEG;C). Key performance indicators, whole-body composition and ac-tivities of digestive enzymes were evaluated at the end of the experiment (64 days). Low dietary lipid levels negatively affected lipid, energy, and amino acid digestibility, and as a result, fish fed the LF diet presented higher nitrogen faecal losses. Still, the decrease in nutrient digestibility was not related to dietary effects on the digestive enzyme activities. The experimental diets did not compromise the activity of pancreatic, gastric, and intestinal digestive enzymes nor feed utilization, but a slight growth impairment was observed in fish fed the LF diet, probably due to the lower amino acid and lipid digestibility. However, a potential benefit of this dietary treatment towards reducing fat accumulation in seabream during summer was observed. Nevertheless, the environmental impact of the nitrogen losses during seabream on-growing should be considered when estimating the sustainability of the production. This study demonstrated that the optimisation of diet formulations should account for the environmental conditions, especially in Mediterranean aquaculture, so the economic and envi-ronmental impacts may be correctly evaluated towards a more sustainable fish production. LA/P/0101/2020 info:eu-repo/semantics/publishedVersion

A two-month feeding trial was conducted to evaluate the effect of partial replacement of fish meal (FM) by soybean protein (SP) alone or in combination with lysine (Lys) and methionine (Met) supplementation in practical diets for silvery-black porgy juveniles (16.7±0.1 g). Seven isoproteic (ca. 50% crude protein) and isoenergetic (ca. 22.4 MJ kg-1) diets were formulated in which 45% (SP45), 60% (SP60) and 75% (SP75) of FM protein were replaced by SP and the control diet (FM) was prepared with FM as the major source of protein. In SP45+, SP60+ and SP75+ diets, 45 to 75% of FM was replaced by SP with supplementing blends of Lys and Met. Growth performance, feed utilization, and protein and lipid digestibility decreased with increasing dietary SP levels (p

Human activities such as trade and transport have increased considerably in the last decades, greatly facilitating the introduction and spread of non-native species at a global level. In the Iberian Peninsula, Fundulus heteroclitus, a small euryhaline coastal fish with short dispersal, was found for the first time in the mid-1970s. Since then, F. heteroclitus has undergone range expansions, colonizing the southern region of Portugal, southwestern coast of Spain and the Ebro Delta in the Mediterranean Sea. Cytochrome b sequences were used to elucidate the species invasion pathway in Iberia. Three Iberian locations (Faro, Cádiz and Ebro Delta) and 13 other locations along the native range of F. heteroclitus in North America were sampled. Results revealed a single haplotype, common to all invasive populations, which can be traced to the northern region of the species’ native range. We posit that the origin of the founder individuals is between New York and Nova Scotia. Additionally, the lack of genetic structure within Iberia is consistent with a recent invasion scenario and a strong founder effect. We suggest the most probable introduction vector is associated with the aquarium trade. We further discuss the hypothesis of a second human-mediated introduction responsible for the establishment of individuals in the Ebro Delta supported by the absence of adequate muddy habitats linking Cádiz and the Ebro Delta. Although the species has a high tolerance to salinity and temperature, ecological niche modelling indicates that benthic habitat constraints prevent along-shore colonisation suggesting that such expansions would need to be aided by human release.

Pseudoplatystoma punctifer posee un gran potencial para la acuicultura, pero la alta tasa de canibalismo existente durante su etapa temprana de vida dificulta por ahora su cultivo a gran escala. Una nutrición adecuada reduce significativamente la incidencia de canibalismo y el conocimiento de la ontogenia funcional del sistema digestivo es esencial para adaptar el protocolo de alimentación a las capacidades digestivas de esta especie y así aumentar la producción de semilla. Por tanto, el objetivo del presente estudio fue analizar la expresión de los principales genes implicados en la digestión (amilasa, tripsina, quimotripsina, pepsinógeno, fosfolipasa, lipoproteína lipasa y neuropéptido Y) durante el desarrollo larvario y juvenil temprano de P. punctifer. Los resultados mostraron que esta especie cuenta con la maquinaria enzimática necesaria para digerir el alimento exógeno antes de la primera alimentación (4 dpf). La expresión de los genes siguió el perfil común de una especie carnívora con un aumento significativo en la expresión de pepsinógeno a partir de los 10 dpf para pasar de una digestión proteica básica en el intestino (tripsina, quimotripsina) a una digestión proteica ácida más eficiente en el estómago (pepsina). Por tanto, P. punctifer está preparada para ser destetada con dietas complejas a partir de 10 dpf. Los resultados también mostraron que el cambio de dieta durante la etapa juvenil moduló la actividad enzimática a nivel transcripcional, por lo que el análisis de la expresión de los precursores enzimáticos digestivos será de utilidad en estudios nutricionales dirigidos a establecer la composición nutricional óptima para esta especie.

The effect of dietary partial replacement of fish meal (FM) by soybean protein (SP) alone or in combination with lysine (Lys) and methionine (Met) supplementation were tested in a 60-days feeding trial for silvery-black porgy (Sparidentex hasta) juveniles. Seven isoproteic (ca. 50% crude protein) and isoenergetic (ca. 22.4 MJ/kg) diets were formulated in which 45% (SP45), 60% (SP60) and 75% (SP75) of FM protein were replaced by SP and the control diet (FM) was prepared with FM as the major source of protein. In SP45+, SP60+ and SP75+ diets, 45 to 75% of FM was replaced by SP with supplementing blends of Lys and Met (98% of purity). The activities of the trypsin, lipase and α-amylase were higher in fish fed SP diets with crystalline amino acids supplementation than in the other groups (P < 0.05). Fish fed SP75 and SP75+ diets had the lowest red blood cell count and hematocrit level (P < 0.05). The results of the current study indicated that anti-nutritional factors in a soy-protein based diet rather than lysine and methionine deficiencies may have adverse effects on digestive enzymes activities and health condition in silvery-black porgy juveniles. info:eu-repo/semantics/publishedVersion

Farmed Senegalese sole (Solea senegalensis) still show a high incidence of vertebral anomalies that limit its intensive production and hamper its economic profitability. A great effort towards understanding how fish species develops and grows in captivity has been undertaken in the last decade, with particular emphasis to how different biotic and abiotic factors affect its skeletal development. Although some work has been performed on its skeletal development and expression patterns of key genes in developmental signaling pathways, a detailed description of the above-mentioned processes is still lacking. Here, the progression of skeletal development of cranial, appendicular and axial skeleton has been described through the implementation of an acid free double staining protocol; while the gene expression pattern of vitamin A (VA) and thyroid hormones (THs) signaling pathways were assessed through quantitative PCR (qPCR) during larval fish development under a standard larval rearing protocol and in Senegalese sole larvae fed with increased dietary VA levels (8-fold increase) during the Anemia feeding phase (from 6 to 27 dph). The ontogenetic study allowed us to identify the onset and follow-up the development of most skeletal structures in this fish species, and to gather some insights on the potential onset of deformities originated at the larval to juvenile transition affecting Senegalese sole rearing. The pro-meta-morphosis stage is when the caudal fin vertebrae are formed, where the most common skeletal deformities are found in Senegalese sole. A highly coordinated expression of VA- and TH-related genes has been revealed during larval to juvenile transition, while a comparative gene expression analysis in larvae fed control and high dietary VA content identified the specific timing of VA and THs signaling disruption through which VA and THs directly or indirectly might increase the incidence of skeletal deformities in this species. The present research work represents an important step forward towards the proper identification of the onset of some skeletal deformities and urge the investigation of nutritional and rearing conditions during the switch of larval behavior - from pelagic to benthonic - in order to overcome them in this important species for southwestern European aquaculture.

The present study describes morphological development of the skeleton in the Persian sturgeon Acipenser persicus and discusses the hypothesis that expression of genes encoding vitamin K‐dependent proteins (VKDP) might be correlated with the mineralization of skeletal tissues during early development in sturgeons. Results showed that development of cartilage started just after hatching (mean ± S.D., 10·9 ± 0·7 mm in total length, LT) in the head and notochord, whereas the first signs of mineralization occurred in the dentary and in the dermopalatine and palatopterygoid elements of the upper jaw, coinciding with the onset of exogenous feeding (20·1 ± 1·5 mm LT). All branchial arch elements developed between 19·3 and 22·3 mm LT, whereas mineralization was only observed in tooth plates associated with the hypobranchial 1 and gill rakers at 20·8 ± 1·5 mm LT and 48·4 ± 6·4 mm LT, respectively. Quantitative real‐time PCR showed that transcripts of VKDP genes including bone Gla protein (bgp), matrix Gla protein (mgp) and Gla rich protein (grp) genes were significantly up‐regulated during the transition to exogenous feeding, supporting hypotheses about relevance of the above‐mentioned genes in chondrogenesis at early developmental stages. The strong mineralization of skeletal elements from 21·5 to 27·3 mm LT (20 days post hatch) was in accordance with the maximal levels of bgp, mgp and grp expression indicating a correlation between development of the skeleton and the expression of VKDP genes. These data are important for evaluating A. persicus larval quality, understanding the influence of rearing biotic and abiotic factors on skeletogenesis and recognizing the occurrence of skeletal deformities in this species. info:eu-repo/semantics/acceptedVersion

Flatfish can provide a reliable model to study developmental disorders in bone tissues occurring during morphogenesis in response to nutritional imbalances. To date, most studies dealing with the effect of dietary essential fatty acids (EFA) on skeletogenesis in fish have focused their investigation on the role of docohexanoic (22:6n−3, DHA) and eicosapentaenoic (20:5n–3, EPA) acids, but only a few have focused on investigating the effects of arachidonic acid (20:4n–6, ARA) on bone during fish larval development. Bone development and composition at larval stage have been demonstrated to be highly sensitive to dietary levels of EFA, in particular the EPA and ARA acids, both precursors for highly bioactive eicosanoids presenting opposite effects on bone metabolism. Since fish are not able to synthesize EFA, they need to obtain them from the diet. However, dietary imbalances in EPA and ARA in flatfish larvae may disrupt bone formation and osteoblast differentiation in skeletal tissues, leading to the incidence of skeletal deformities, reduced mineralization and problems of bone remodelling in the cranial region associated with impaired eye migration. These anomalies in skeletal structures are one of the most important factors that affect flatfish larval quality and hamper their production. Thus, we have reviewed the current state of knowledge about the effects of dietary ARA contents on skeletogenesis in Senegalese sole (Solea senegalensis), one of the main flatfish species cultured in Europe. Their larval quality still suffers for a high incidence of skeletal anomalies induced by dietary imbalances during metamorphosis.

Terrestrial animal byproduct meals, including nonruminant blood meal and blood products, represent the largest and largely untapped safe source of animal protein available within the international market for the aquafeed industry. Spray-dried blood and spray-dried plasma (SDP) proteins have long been recognized as high-quality feed ingredients for farmed animals. In this study, we evaluated the inclusion of SDP from porcine blood (SDPP) in growing diets for gilthead sea bream. Three isonitrogenous (CP = 51.2%) and isolipidic (fat = 12.4%) diets manufactured by cold extrusion (0.8 to 1.5 mm pellet size) were prepared by substituting high-quality fish meal with 0, 3, and 6% SDPP. The diets were tested for a period of 60 d at 22°C with 4 replicates each (400-L cylindroconical tanks, 150 fish per tank, and initial density = 0.5 kg/ m3). The SDPP inclusion in diets for gilthead sea bream fingerlings were evaluated in terms of growth performance, feed utilization, histological organization of the intestinal mucosa, activity of oxidative stress enzymes (catalase, glutathione S-transferase, glutathione peroxidase, and glutathione reductase) in the intestine, and nonspecific serum immune parameters (lysozyme and bactericidal activity). Results from this study indicated that dietary SDPP promoted fish growth in terms of BW and length; fish fed 3% SDPP were 10.5% heavier (P < 0.05) than those fed the control diet. Spray-dried plasma from porcine blood modulated the activity of the antioxidative defenses in the intestine (P < 0.05) and increased the density of goblet cells in the intestine (P < 0.05) and benefited the host by providing an effective immune barrier against gut pathogenic microbiota. The nonspecific serum immune response in fish fed diets with SDPP was greater (P < 0.05) than in fish fed the control diet. These results indicated that the inclusion of SDPP in gilthead sea bream feed could be beneficial for the fish by enhancing intestinal and serum innate immune function and the activity of antioxidative stress enzymes of the intestine and promoting growth performance. info:eu-repo/semantics/publishedVersion

The aim of the study was to evaluate the influence of different dietary protein and lipid levels and their ratios on larval growth, survival and the incidence of cannibalism in Pseudoplatystoma punctifer. Larvae were raised in a recirculation system from 3 to 26days post-fertilization (dpf) (2-25days post hatching, dph) at an initial density of 40 larvae L-1, 27.8 +/- 0.65 degrees C and 0L:24D photoperiod. Larvae were fed from 4 to 12 dpf with Artemia nauplii and weaned onto four different compound diets from 13 dpf within 3days, then fed exclusively with these diets until 26 dpf. These diets contained 30:15, 30:10, 45:15 or 45:10 protein:lipid (P:L) (in % of dry matter) levels. A control group was fed Artemia nauplii until 17 dpf and weaned thereafter with the 45P:10L compound diet. The experiment was carried out in triplicate. Results showed higher growth and survival rates and lower incidence of cannibalism in the group fed the 45P:15L diet than in the other treatments. Differences in larval survival and growth performance were associated with the higher protein and lipid content rather than the protein:lipid ratio of this diet. When comparing diets with the same protein level, the increase in dietary lipid led to an improvement in growth, suggesting that energy from lipids spares protein for growth in P.punctifer fingerlings. An Artemia feeding period longer than 12 dpf did not improve larval growth or survival.

Biology of European Seabass presents up-to-date reviews on key topics of seabass biology, written by leading scientific experts with extensive knowledge of seabass as well as their respective field of expertise. The book covers the biology and ecology of the different sea basses and the latest findings in molecular biology, physiology, and beh; International audience; Marine fish larval culture is one of the main bottlenecks in the aquaculture industry. At hatching, most of the organs of marine fish larvae are not fully developed, and developmental processes initiated during embryogenesis continue during larval development in order to ensure the proper ontogenesis of organs and associated physiological functions, essential for the survival of individuals. Consequently, during the first weeks of life, marine fish larvae undergo significant morphological and physiological modifications to acquire all the adult features by the end of the larval period. This phase is certainly the most critical in the life cycle of fish, not only in natural environments, but also under controlled conditions. In aquaculture, in spite of the many advances made to control environmental cues, this stage of production can still suffer from substantial mortality impaired larval quality, influencing the overall performance of the rearing production, whose final objective is the obtention of enough fry of good quantity and quality for on-growing purposes.

The effect of high dietary levels of arachidonic acid (ARA) on the eye migration and cranial bone remodelling processes in Senegalese sole Solea senegalensis early juveniles (age: 50_days post hatch) was evaluated by means of geometric morphometric analysis and alizarin red staining of cranial skeletal elements. The incidence of normally pigmented fish fed the control diet was 99·1_±_0·3% (mean_±_s.e.), whereas it was only 18·7_±_7·5% for those fed high levels of ARA (ARA-H). The frequency of cranial deformities was significantly higher in fish fed ARA-H (95·1_±_1·5%) than in those fed the control diet (1·9_±_1·9%). Cranial deformities were significantly and negatively correlated with the incidence of normally pigmented animals (r2 = _0·88, P < 0·001, n = 16). Thus, fish displaying pigmentary disorders differed in the position of their eyes with regard to the vertebral column and mouth axes, and by the interocular distance and head height, which were shorter than in fish not displaying pigmentary disorders. In addition to changes in the positioning of both eyes, pseudoalbino fish showed some ARA-induced osteological differences for some of the skeletal elements from the splanchnocranium (e.g. right premaxillary, dentary, angular, lacrimal, ceratohyal and branchiostegal rays) and neurocranium (e.g. sphenotic, left lateral ethmoid and left frontal) by comparison to normally pigmented specimens. Pseudoalbino fish also had teeth in both lower and upper jaws. This is the first study in Pleuronectiformes that describes impaired metamorphic relocation of the ocular side eye, the right eye in the case of S. senegalensis, whereas the left eye migrated into the ocular side almost normally

The appearance of the pseudo-albino phenotype was investigated in developing Senegalese sole (Solea senegalensis, Kaup 1858) larvae at morphological and molecular levels. In order to induce the development of pseudo-albinos, Senegalese sole larvae were fed Artemia enriched with high levels of arachidonic acid (ARA). The development of their skin pigmentation was compared to that of a control group fed Artemia enriched with a reference commercial product. The relative amount of skin melanophores, xanthophores and iridophores revealed that larval pigmentation developed similarly in both groups. However, results from different relative proportions, allocation patterns, shapes and sizes of skin chromatophores revealed changes in the pigmentation pattern between ARA and control groups from 33 days post hatching onwards. The new populations of chromatophores that should appear at post-metamorphosis were not formed in the ARA group. Further, spatial patterns of distribution between the already present larval xanthophores and melanophores were suggestive of short-range interaction that seemed to be implicated in the degradation of these chromatophores, leading to the appearance of the pseudo-albino phenotype. The expression profile of several key pigmentation-related genes revealed that melanophore development was promoted in pseudo-albinos without a sufficient degree of terminal differentiation, thus preventing melanogenesis. Present results suggest the potential roles of asip1 and slc24a5 genes on the down-regulation of trp1 expression, leading to defects in melanin production. Moreover, gene expression data supports the involvement of pax3, mitf and asip1 genes in the developmental disruption of the new post-metamorphic populations of melanophores, xanthophores and iridophores.

To improve the understanding of the incidence of skeletal deformities in Senegalese sole (Solea senegalensis), a feeding trial was carried out to evaluate the effect of increasing dietary arachidonic acid (ARA) levels during the Artemia feeding period on larval growth and skeletogenesis. Larvae were fed from 8 to 50 days post hatching (dph) with Artemia nauplii enriched with three different levels of ARA: ARA-Low, ARA-Medium and ARA-High (1.0, 4.5 and 7.0% ARA of total fatty acids, respectively). Increasing levels of dietary ARA did not affect significantly the survival. However, it influenced growth; larvae from the ARA-M group presented the highest values of final standard length and dry weight (11.36 +/- 0.47 mm and 5.86 +/- 1.06 mg at 50 dph, respectively) and larvae from the ARA-H group the lowest ones (9.53 +/- 0.27 mm and 2.47 +/- 0.26 mg at 50 dph). The skeleton of larvae fed the ARA-M diet tended to be more calcified at 15 dph than that of larvae fed ARA-L and ARA-H diets. Larvae from the ARA-M group tended to show a higher incidence of fusion of hypurals 3 and 4 (34.4 +/- 3.1%) at 50 dph than the larvae from the other groups (18.7 +/- 1.6%, in average). The latter results reflected a trend to a higher degree of skeletal development rather than a deformity, this being in agreement with the higher larval growth of this group. Besides, ARA levels did not affect significantly the incidence of total skeletal deformities (41.4 +/- 1.5% in average). Larvae from all dietary treatments mostly displayed fusions of the vertebra 43 and 44 (32.2 +/- 1.3% in average). The amount of 4.5% of total fatty acid of dietary ARA during Artemia feeding period promoted the best growth and proper skeletogenesis in Senegalese sole larvae.

Initially we characterised growth responses to altered nutritional input at the transcriptional and tissue levels in the fast skeletal muscle of juvenile gilthead sea bream. Fish reared at 21-22 degrees C (range) were fed a commercial diet at 3% body mass d(-1) (non-satiation feeding, NSF) for 4 weeks, fasted for 4d (F) and then fed to satiation (SF) for 21d. 13 out of 34 genes investigated showed consistent patterns of regulation between nutritional states. Fasting was associated with a 20-fold increase in MAFbx, and a 5-fold increase in Six1 and WASp expression, which returned to NSF levels within 16h of SF. Refeeding to satiation was associated with a rapid (

How lipid content and composition in the diet is utilized by the various organs and tissues of fish is reflected in their structure, such as the intestine through which dietary lipids are digested and absorbed, the vascular system which is involved in their transport, and the liver where lipids are stored and metabolized. However, no study has been conducted to compare the effect of different diets containing different levels of highly unsaturated fatty acids (HUFA) and essential fatty acids (EFA) on lipid deposition in fish larvae and early juveniles. Thus, we evaluated the effects of six isolipidic diets (enriched Artemia sauna), differing in their fatty acid profile, on the lipid accumulation patterns in selected target tissues (intestine, liver and vascular system) in Senegalese sole (Solea senegalensis) larvae and early juveniles. Results showed that the profile of fat accumulation in these three tissues was significantly affected by the dietary treatments, the developmental stage of the fish (premetamorphosis, metamorphosis or postmetamorphosis), as well as by the interaction between these two factors that were responsible for changes in the histological organization of the tissues. Histological results revealed that a slight variation in the EFA levels (e.g. EPA, DHA or ARA) or in their ratios (EPA/DHA, ARA/EPA, ARA/DHA, (n-3)/(n-6) HUFA, OA/PUFA) modified the metabolism of lipids and disrupted the pattern of lipid accumulation in the target tissues, leading to intestinal and hepatic steatosis.

Several methods and procedures exist for the diagnosis of skeletal disorders in fish. X-ray is one of the most reliable diagnosis technologies for medium-sized and large animals, whereas external examination is only of value in animals with extreme and prominent deformities. In small fish (e.g. juveniles or larvae), whole mount staining with alizarin red and/or alcian blue is advisable, although soft-tissue X-ray may be also used. Under this context, the study of the fish skeleton and its morphological and developmental disorders requires an accurate visualization of three-dimensional structures, but few widely applicable methods exist for non-destructive whole-volume imaging of animal tissues. In this sense, computed tomography (CT) has been recently suggested as an alternative or complementary imaging method for the early diagnosis of skeletal deformities, as well as a valuable tool for the current research on the causes and prevention of these anatomical disorders. In this study, we have analysed the skeleton of a 9.3 kg meagre (Argyrosomus regius) by means of standard X-rays (SEDECAL APR-VET 20 KW) and computerized X-ray tomography (HiSpeed Zx/i, General Electric Healthcare) and compared both imaging methods. The vertebral column of the examined specimen was composed by 24 vertebral bodies (including the urostyle) with a regional variation in the morphology of centrums along the vertebral axis. Both imaging methodologies allowed the clear visualization and identification of bony structures composing the skeleton of the meagre. In addition, the CT also allowed performing axial cuts of the meagre in which it was possible to differentiate tissues of different density (e.g. muscle, fat, bone), due to their different attenuation of the X-rays measured in Hounsfield scale. A general view of the potential of such imaging techniques, considering both their advantages and limitations is discussed.

Retinoic acid (RA) is a potent morphogenetic nutrient that plays an essential role in the processes of morphogenesis, skeletogenesis and pigmentation of fishes by activating the expression of over 500 genes. However, still little is known about the transcriptional cascades mediated by RA in flatfish species. Therefore, the aim of this study was to evaluate the effects of RA during the larval development and metamorphosis of Senegalese sole and to determine the transcriptional responses of genes involved in RA metabolism and action. In a first experiment, pre-metamorphic larvae (7 days after hatching, dah) were treated with an inhibitor of RA synthesis (DEAB) until the end of metamorphosis (20dah). In a second experiment, post-metamorphic larvae pretreated for 3 days with DEAB and DMSO (solvent of DEAB) were subdivided into three additional tanks to which all-trans RA (ATRA) and TTNPB (rar agonist) were added. In each experiment, samples were taken at different times to quantify the expression of genes involved in RA synthesis (rdh10a, raldh2), degradation (cyP26a1), metabolism (rbp1, rbp4, crabp1a), mediators of its action (retinoic acid nuclear receptors, rarα1, rarα2, rarγ##, rxrα, rxrβ1, rxrβ2, rorβ, rarres3) and other RA-related pathways (thrαa, thrαb, thrβ). Retinoic acid (RA) is a potent morphogenetic nutrient that plays an essential role in the processes of morphogenesis, skeletogenesis and pigmentation of fishes by activating the expression of over 500 genes. However, still little is known about the transcriptional cascades mediated by RA in flatfish species. Therefore, the aim of this study was to evaluate the effects of RA during the larval development and metamorphosis of Senegalese sole and to determine the transcriptional responses of genes involved in RA metabolism and action. In a first experiment, pre-metamorphic larvae (7 days after hatching, dah) were treated with an inhibitor of RA synthesis (DEAB) until the end of metamorphosis (20dah). In a second experiment, post-metamorphic larvae pretreated for 3 days with DEAB and DMSO (solvent of DEAB) were subdivided into three additional tanks to which all-trans RA (ATRA) and TTNPB (rar agonist) were added. In each experiment, samples were taken at different times to quantify the expression of genes involved in RA synthesis (rdh10a, raldh2), degradation (cyP26a1), metabolism (rbp1, rbp4, crabp1a), mediators of its action (retinoic acid nuclear receptors, rarα1, rarα2, rarγ##, rxrα, rxrβ1, rxrβ2, rorβ, rarres3) and other RA-related pathways (thrαa, thrαb, thrβ). &nbsp

The presence of sublethal morphological deformities represents one of the main bottleneck of the industrial finfish hatchery production, resulting in major economic loss due to reduced growth and marketing ability of the final product, that has to be transformed (filets) or sold for fish flour. Furthermore, the elimination of deformed fishes from the productive cycle needs for periodic selections at present carried out by manual sorting. This represents an additional economic cost, and a stress for fishes. This work benefits from participation in LARVANET COST action FA0801.