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The increasing expansion of the invasive Asian alga Rugulopteryx okamurae along the Andalusian coasts is a major challenge to marine biodiversity, and urgent coordinated measures are required for its removal or elimination. Among the different actions, the biotechnological valorisation could be a strategy for the management of alien biomass within the frame of the Blue Economy. This work evaluates the potential of R. okamurae biomass, either raw or processed by biotechnological treatments based on enzymatic hydrolysis and fermentation processes, to be used as a dietary ingredient in juvenile seabass (Dicentrarchus labrax). These treatments, intended primarily to improve the nutrient availability, might also decrease the content of undesirable and potentially harmful algal metabolites, such as the diterpenoid dilkamural. To this end, a 90-day feeding trial was carried out using four experimental diets containing 5% (w/w) crude or processed R. okamurae biomass. The results obtained revealed that the inclusion in the diet of raw R. okamurae caused adverse effects on fish growth, yielding lower values than those of the control group (p < 0.05), although this detrimental effect was negligible when the algae was processed prior to its inclusion in the experimental feeds. In terms of muscle composition, diets supplemented with the algal biomass induced an increase in protein content, especially in fish fed with pre-treated biomass. Qualitative differences (p < 0.05) were also found in muscle fatty acid profile, with a significant increase in ARA and DHA contents in fish fed on algae-supplemented diets. A significant reduction (p < 0.05)in muscle and liver lipid oxidation was evidenced in fish fed the algae-enriched diets, especially with treated biomass. Finally, 5% R. okamurae raw biomass caused negative effects on gut functionality, although these effects were not observed when the algal biomass was previously processed. In conclusion, the results revealed the potential

Chelon labrosus represents a promising species for current aquaculture to lean towards a more sustainable model. The control of reproduction in captivity is essential to develop the industrial production of new species. This work adds to the knowledge of the reproductive aspects of males and females of this species. We aim to (1) develop a methodology for sex identification of reproductive and prereproductive specimens of the studied species based on the plasma levels of steroid hormones—estradiol (E2) and 11-ketotestosterone (11-KT); (2) determine the maturity evolution of the females throughout the spawning season by gonadal biopsy; and (3) describe sperm quality throughout the breeding season (volume, motility, density). The results show that an 11-KT/E2 ratio > 0.4 is 100% effective in distinguishing males from females, provided that individuals present a size greater than that of first sexual maturity. A double trend was observed in the development of oocytes, with an increase in the initial diameter until the middle of the spawning season, followed by a divergence of the group, with some females continuing the maturation process and others going into regression. Sperm data show stable quality at the beginning and in the middle of the spawning season and a significant loss of quality at the end of the reproductive period. The present study also shows that, between the beginning and the middle of the reproductive season, males of this species can recover sperm volume removed by stripping.

[EN] Different strategies have been followed to improve the aquaculture of main European farmed fish, such as genetic selection, refinements in culture conditions or enhanced feed formulation and management. However, more knowledge is required to exploit fish phenotypic plasticity to obtain those that better match aquaculture or market conditions. The overall objective of this mini-review is to identify the latest productive traits recently performed, mainly in commercial carnivorous species, and underlying biological processes that would be susceptible to improve the competitivity of aquaculture sector through nutritional issues. Thus, this work is framed within the concepts of Circular Economy and Blue Growth, where it is intended to point out the use of natural compounds extracted from seaweeds, microalgae and by-products of the industry for their inclusion in aquafeeds, allowing a more efficient use of more sustainable vegetable protein sources, and also to evaluate if these nutraceutical compounds counteract detrimental effects observed by nutritional interventions or environmentally challenged., [ES] La producción acuícola ha seguido diferentes estrategias para su optimización a lo largo de las últimas décadas, como el desarrollo de la selección genética, la mejora de las condiciones de cultivo, o el avance en la formulación y gestión de los piensos. Sin embargo, se requiere más conocimiento para explotar la plasticidad fenotípica de los peces para obtener aquellos que se ajusten mejor a las condiciones de la acuicultura o del mercado. El objetivo general de esta mini-revisión es identificar los últimos avances realizados recientemente, principalmente en especies carnívoras comerciales, y los procesos biológicos subyacentes que serían susceptibles de mejorar la competitividad del sector acuícola a través de intervenciones nutricionales. Así, este trabajo se enmarca dentro de los conceptos de Economía Circular y Crecimiento Azul, donde se pretende señalar el uso de compuestos naturales extraídos de algas, microalgas y subproductos de la industria para su inclusión en alimentos acuícolas, permitiendo un uso más eficiente de fuentes de proteínas vegetales más sostenibles, y también evaluar si estos compuestos nutracéuticos son capaces de contrarrestar los efectos perjudiciales observados por las formulaciones inadecuadas o desafiados por factores ambientales estresantes.

Growth rate in farmed fish is the phenotypic trait of major relevance for the aquaculture industry. Several strategies have been followed to increase growth rate in fish such as genetic selection and improvements in diet formulation. Somatic growth in fish, as in other vertebrates, is mainly controlled by the growth hormone (GH) / insulin-like growth factor I (IGF-I) axis. The molecular and physiological features of this axis have been thoroughly studied in several vertebrates. In fish, GH/IGF-I axis functionality in fish depends on endogenous and environmental factors such as genetic polymorphisms and nutritional status. There are now several evidences that fish GH-IGF-I axis can be modulated also by epigenetic mechanisms such as DNA methylation. However, the role of epigenetics in regulating this axis in fish is far from being understood as results, in addition to sparse, are poorly consistent among species regarding genes affected. The present study aimed to evaluate ex-vivo models for epigenetic studies in Sparus aurata and to provide the first assessment in this species of the putative role of DNA methylation on the modulation of GH/IGF-I axis.

Temperature is a key factor for achieving optimum fish growth and keep the welfare of the culture. Indeed, an incorrect temperature can affect ingestion, transit, digestion, assimilation and metabolism. Furthermore, this is magnified in a fastgrowing fish such as the greater amberjack (Seriola dumerili). The culture of this species is becoming more and more important in the Mediterranean coasts mainly because of its fast development, its meat quality and its good acceptance in the market. For all these reasons, it is of utmost importance to establish a proper temperature, especially in RAS systems where this parameter can be modified quite easily, although its monitoring is especially important to avoid secondary artifacts that could compromise the metabolic and intestinal well-being of cultured fish. Taking all this into account, the aim of this study was to establish the consequences of water temperature on welfare, metabolic orchestration and intestinal integrity of greater amberjack juveniles accompanying the observed differences in growth performance (Yúfera et al., this conference).

[EN] Aquaculture is the best bet for the future to face the great challenge of providing food to a population that will reach 9 billion people in 2050. However, to increase the production performance of aquaculture in a sustainable way, it is necessary to develop strategies, such as species diversification or the use of more sustainable diets. In this respect, the greater amberjack (Seriola dumerili) is a good candidate both for its high biological and economic potential. However, as a carnivorous species, it has high protein requirements, most of which from fish meal. Therefore, it is essential to replace ingredients of animal origin with more sustainable ones such as plant raw materials. However, diets with a high content of vegetable ingredients can affect the bioavailability and digestibility of nutrients causing negative effects on fish growth and health. Nevertheless, the use of biotechnological pretreatments of plant ingredients and the inclusion of nutraceutical compounds have allowed to improve the use of these nutrients, providing good growth and health status of a highly carnivorous species such as greater amberjack., [ES] La acuicultura es la mejor apuesta de futuro para hacer frente al gran desafío de proporcionar alimentos a una población que superará los 9 billones de personas en 2050. Sin embargo, para incrementar el rendimiento de la producción acuícola de manera sostenible es necesario desarrollar estrategias como la diversificación de especies o el uso de dietas más sostenibles. En este sentido, la seriola o pez limón (Seriola dumerili), es un buen candidato tanto por su gran potencial biológico como económico. Sin embargo, como especie carnívora, presenta unos altos requerimientos de proteínas, procedentes la mayor parte de las harinas de pescado. Por tanto, es imprescindible la sustitución de ingredientes de origen animal por otros más sostenibles como las materias primas vegetales. Aun así, dietas con un alto contenido de ingredientes vegetales pueden afectar a la biodisponibilidad y digestibilidad de los nutrientes causando efectos negativos sobre el crecimiento y la salud de los peces. Sin embargo, el uso de pretratamientos biotecnológicos de los ingredientes vegetales y la inclusión de compuestos nutraceúticos han permitido un buen uso de los nutrientes presentes en estas dietas, proporcionando un buen crecimiento y estado de salud en una especie altamente carnívora como la seriola.

A good knowledge of the potential effects of water temperature on feeding and on-growing process is of primary importance to optimize the fish production. Temperature modulates ingestion, transit, digestion, assimilation, metabolism and ultimately feed utilization and growth rate. These two last parameters, together with the cost of feeds and energy, are necessary data for producers to make decisions. The production in indoor facilities with temperature control is depending on energy cost while in outdoor facilities (ponds and cages) it depends on environmental temperature. The effect of temperature is more noticeable in fast growing fish, as the greater amberjack (Seriola dumerili), a species of great interest for the aquaculture industry worldwide. Currently, its cultivation is expanding in the Mediterranean countries. Therefore, it constitutes a good model to study the consequences of an increased temperature. In this study, we examined the ingestion, digestive enzyme activities, metabolites in plasma and liver, antioxidant response in the liver and the integrity and electrogenic amino acid transport in the intestine, in greater amberjack juveniles growing at three different temperatures. The final aim was to elucidate the mechanisms behind feed utilization that justify the growth differences and to provide a useful informative basis to the productive sector.

This study aimed to verify the effect of different feeding and stocking conditions during 14 days on the gene expression of several hormones and enzymes related to the stress cascade and metabolic parameters in silver catfish Rhamdia quelen under the following experimental conditions: 1) fed at low stocking density (2.5 kg m-3, LSD-F); 2) fed at high stocking density (32 kg m-3, HSD-F); 3) food-deprived at LSD (LSD-FD); and 4) food-deprived at HSD (HSD-FD). Fish from LSD-F and HSD-F groups were fed daily (1 % of their body mass), while fish from food-deprived groups (LSD-FD and HSD-FD) were not fed during the experimental time. Plasma metabolic parameters (glucose, lactate, triglycerides, and proteins) and hepatosomatic index (HSI) were evaluated. In addition, mRNA expression of genes related to the stress axis (crh, pomca, pomcb, nr3c2, star, hsd11b2 and hsd20b), heat shock protein family (hsp90 and hspa12a), sodium-dependent noradrenaline transporter (slc6a2), and growth axis (gh and igf1) were also assessed. Specific growth rate and HSI decreased in food-deprived fish regardless of stocking density. The HSD-FD group showed weight loss compared to the HSD-F, LSD-F, and LSD-FD groups. Plasma glucose and triglycerides were reduced in food-deprived groups, while lactate and protein levels did not change. The expression of key players of the stress response (crh, pomca, pomcb, hsd11b2, nr3c2, and hsp90b) and growth (gh and igf1) pathways were differently regulated depending on the experimental condition, whereas no statistical difference between treatments was found for hsd20b, scl6a2, hspa12a, and star mRNAs expression. This study suggests that LSD acts as a stressor affecting negatively the physiological status of fed fish, as demonstrated by the reduction in growth rates, altered metabolic orchestration, and a higher crh mRNA expression. In addition, food deprivation also increased mRNA expression of other assessed genes (nr3c2, hsp90b, pomca, and pomcb) in fish fr

In keeping with the premises of Blue Circular Economy in the European Union, the present study explored the possibility of using the invasive brown alga Rugulopteryx okamurae in aquafeeds for European sea bass (Dicentrarchus labrax). Assuming the raw algae biomass could negatively impact animal performance, four experimental formulations were prepared, by including macroalgae material at 5%, using crude (CR), enzymatically hydrolysed and fermented (EF), enzymatically hydrolysed (E), or fermented (F) R. okamurae biomass, which we tested against a control feed (CT). To evaluate the effects of the experimental diets, besides animal growth performance and biometric parameters, we devised a toolbox focused on the intestine and intestinal function: i) ex-vivo epithelial resistance and permeability in Ussing chambers; ii) microbiota composition through NGS; iii) expression profiles of selected markers for epithelial integrity, transport, metabolism, and immune response, by qPCR. Our results show differentiated allometric growth among diets, coupled with intestinal epithelium alterations in permeability, integrity, and amino acid transport. Additionally, evidence of microbiota dysbiosis and contrasting immune responses between experimental diets, i.e. pro-inflammatory vs. anti-inflammatory, are also described. In conclusion, we believe that R. okamurae could be a suitable resource for aquafeeds for the European sea bass, although its use requires a pre-treatment before inclusion. Otherwise, while the fish still have a positive growth performance, the gastrointestinal tract pays a toll on the integrity, transport, and inflammatory processes.