Tissue-Specific Orchestration of Gilthead Sea Bream Resilience to Hypoxia and High Stocking Density

Differential Reshaping of Skin and Intestinal Microbiota by Stocking Density and Oxygen Availability in Farmed Gilthead Sea Bream (Sparus aurata): A Behavioral and Network-Based Integrative Approach

Fish were kept for six weeks at three different initial stocking densities and water O2 concentrations (low-LD, 8.5 kg/m3 and 95-70% O2 saturation; medium-MD, 17 kg/m3 and 55-75% O2 saturation; high-HD, 25 kg/m3 and 60-45% O2 saturation), with water temperature increasing from 19 °C to 26-27 °C. The improvement in growth performance with the decrease in stocking density was related to changes in skin and intestinal mucosal microbiomes. Changes in microbiome composition were higher in skin, with an increased abundance of Alteromonas and Massilia in HD fish. However, these bacteria genera were mutually exclusive, and Alteromonas abundance was related to a reactive behavior and systemic growth regulation via the liver Gh/Igf system, while Massilia was correlated to a proactive behavior and a growth regulatory transition towards muscle rather than liver. At the intestinal level, microbial abundance showed an opposite trend for two bacteria taxa, rendering in a low abundance of Reyranella and a high abundance of Prauserella in HD fish. This trend was correlated with up-regulated host gene expression, affecting the immune response, epithelial cell turnover, and abiotic stress response. Most of the observed responses are adaptive in nature, and they would serve to infer new welfare indicators for increased stress resilience.

The Expansion of Sirtuin Gene Family in Gilthead Sea Bream (Sparus aurata)-Phylogenetic, Syntenic, and Functional Insights across the Vertebrate/Fish Lineage

The Sirtuin (SIRT1-7) family comprises seven evolutionary-conserved enzymes that couple cellular NAD availability with health, nutrition and welfare status in vertebrates. This study re-annotated the sirt3/5 branch in the gilthead sea bream, revealing three paralogues of sirt3 (sirt3.1a/sirt3.1b/sirt3.2) and two of sirt5 (sirt5a/sirt5b) in this Perciform fish. The phylogeny and synteny analyses unveiled that the Sirt3.1/Sirt3.2 dichotomy was retained in teleosts and aquatic-living Sarcopterygian after early vertebrate 2R whole genome duplication (WGD). Additionally, only certain percomorphaceae and gilthead sea bream showed a conserved tandem-duplicated synteny block involving the mammalian-clustered sirt3.1 gene (psmd13-sirt3.1a/b-drd4-cdhr5-ctsd). Conversely, the expansion of the Sirt5 branch was shaped by the teleost-specific 3R WGD. As extensively reviewed in the literature, human-orthologues (sirt3.1/sirt5a) showed a high, conserved expression in skeletal muscle that increased as development advanced. However, recent sirt3.2 and sirt5b suffered an overall muscle transcriptional silencing across life, as well as an enhanced expression on immune-relevant tissues and gills. These findings fill gaps in the ontogeny and differentiation of Sirt genes in the environmentally adaptable gilthead sea bream, becoming a good starting point to advance towards a full understanding of its neo-functionalization. The mechanisms originating from these new paralogs also open new perspectives in the study of cellular energy sensing processes in vertebrates.

Transcriptomic changes behind Sparus aurata hepatic response to different aquaculture challenges: An RNA-seq study and multiomics integration

Gilthead seabream (Sparus aurata) is an important species in Mediterranean aquaculture. Rapid intensification of its production and sub-optimal husbandry practices can cause stress, impairing overall fish performance and raising issues related to sustainability, animal welfare, and food safety. The advent of next-generation sequencing technologies has greatly revolutionized the study of fish stress biology, allowing a deeper understanding of the molecular stress responses. Here, we characterized for the first time, using RNA-seq, the different hepatic transcriptome responses of gilthead seabream to common aquaculture challenges, namely overcrowding, net handling, and hypoxia, further integrating them with the liver proteome and metabolome responses. After reference-guided transcriptome assembly, annotation, and differential gene expression analysis, 7, 343, and 654 genes were differentially expressed (adjusted p-value < 0.01, log2|fold-change| >1) in the fish from the overcrowding, net handling, and hypoxia challenged groups, respectively. Gene set enrichment analysis (FDR < 0.05) suggested a scenario of challenge-specific responses, that is, net handling induced ribosomal assembly stress, whereas hypoxia induced DNA replication stress in gilthead seabream hepatocytes, consistent with proteomics and metabolomics' results. However, both responses converged upon the downregulation of insulin growth factor signalling and induction of endoplasmic reticulum stress. These results demonstrate the high phenotypic plasticity of this species and its differential responses to distinct challenging environments at the transcriptomic level. Furthermore, it provides significant resources for characterizing and identifying potentially novel genes that are important for gilthead seabream resilience and aquaculture production efficiency with regard to fish welfare.

Understanding how high stocking densities and concurrent limited oxygen availability drive social cohesion and adaptive features in regulatory growth, antioxidant defense and lipid metabolism in farmed gilthead sea bream (Sparus aurata)

The study combined the use of biometric, behavioral, physiological and external tissue damage scoring systems to better understand how high stocking densities drive schooling behavior and other adaptive features during the finishing growing phase of farmed gilthead sea bream in the Western Mediterranean. Fish were grown at three different final stocking densities (LD, 8.5 kg/m3; MD, 17 kg/m3; HD, 25 kg/m3). Water oxygen concentration varied between 5 and 6 ppm in LD fish to 3-4 ppm in HD fish with the summer rise of water temperature from 19°C to 26°C (May-July). HD fish showed a reduction of feed intake and growth rates, but they also showed a reinforced social cohesion with a well-defined endogenous swimming activity rhythm with feeding time as a main synchronization factor. The monitored decrease of the breathing/swimming activity ratio by means of the AEFishBIT data-logger also indicated a decreased energy partitioning for growth in the HD environment with a limited oxygen availability. Plasma glucose and cortisol levels increased with the rise of stocking density, and the close association of glycaemia with the expression level of antioxidant enzymes (mn-sod, gpx4, prdx5) in liver and molecular chaperones (grp170, grp75) in skeletal muscle highlighted the involvement of glucose in redox processes via rerouting in the pentose-phosphate-pathway. Other adaptive features included the depletion of oxidative metabolism that favored lipid storage rather than fatty acid oxidation to decrease the oxygen demand as last electron acceptor in the mitochondrial respiratory chain. This was coincident with the metabolic readjustment of the Gh/Igf endocrine-growth cascade that promoted the regulation of muscle growth at the local level rather than a systemic action via the liver Gh/Igf axis. Moreover, correlation analyses within HD fish displayed negative correlations of hepatic transcripts of igf1 and igf2 with the data-logger measurements of activity and respiration, whereas the opposite was found for muscle igf2, ghr1 and ghr2. This was indicative of a growth-regulatory transition that supported a proactive instead of a reactive behavior in HD fish, which was considered adaptive to preserve an active and synchronized feeding behavior with a minimized risk of oxidative stress and epidermal skin damage.

Hypoxia stress induces hepatic antioxidant activity and apoptosis, but stimulates immune response and immune-related gene expression in black rockfish Sebastes schlegelii

Dissolved oxygen concentrations both in the open ocean and coast have been declining due to the interaction of global climate change and human activity. Fish have evolved different adaptative strategies to cope with possibly damage induced by hypoxic environments. Black rockfish as important economic fish widely reared in the offshore sea cage, whereas related physiological response subject to hypoxia stress remained unclear. In this study, hepatic anti-oxidant enzymes (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GSH-Px]), aminotransferase (AST) and alanine aminotransferase (ALT) activities, lipid peroxidation (LPO), malondialdehyde (MDA) and glutathione (GSH) content, immunological parameters and the expression of apoptosis (bax, bcl2, p53, caspase3, xiap) and immune-related genes (c3, il-1β, ccl25, saa, hap, isg15) of black rockfish were determined during hypoxia and reoxygenation to illustrate the underlying defense response mechanisms. Results showed that hypoxia stress remarkably increased hepatic LPO and MDA content, AST and ALT activity and proportion of pyknotic nucleus. Hepatic SOD, CAT and GSH-Px activity manifested similar results, whereas GSH levels significantly decreased under hypoxia stress. The apoptosis rate of hepatocyte increased during hypoxia stress and reoxygenation. Meanwhile, p53, caspase3, bax and xiap mRNAs and bax/bcl2 rations were significantly up-regulated under hypoxia stress. However, bcl2 mRNA was significantly down-regulated. Interestingly, hypoxia stress significantly increased NBT-positive cell percent, phagocytic index, respiratory burst and ACH50 activity, and lysozyme activity. The mRNA levels of c3, ilβ, ccl25, saa, hap and isg15 were significantly up-regulated in the liver, spleen and head-kidney under hypoxia stress. The above parameters recovered to normal status after reoxygenation for 24 h Thus, hypoxia stress impairs hepatic antioxidant capacity, induces oxidative damage and apoptosis via the xiap-p53-bax-bcl2 and the caspase-dependent pathways, but enhances host immunity by regulating nonspecific immune indices and related genes expression to maintain homeostasis in black rockfish. These findings will help fully understand the hypoxia tolerance mechanisms of black rockfish and provide more data for offshore open ocean farming.

Metabolomics and Transcriptomics Reveal the Response Mechanisms of Mikania micrantha to Puccinia spegazzinii Infection

Mikania micrantha is one of the 100 worst invasive species globally and can cause significant negative impacts on agricultural and forestry economics, particularly in Asia and the Pacific region. The rust Puccinia spegazzinii has been used successfully as a biological control agent in several countries to help manage M. micrantha. However, the response mechanisms of M. micrantha to P. spegazzinii infection have never been studied. To investigate the response of M. micrantha to infection by P. spegazzinii, an integrated analysis of metabolomics and transcriptomics was performed. The levels of 74 metabolites, including organic acids, amino acids, and secondary metabolites in M. micrantha infected with P. spegazzinii, were significantly different compared to those in plants that were not infected. After P. spegazzinii infection, the expression of the TCA cycle gene was significantly induced to participate in energy biosynthesis and produce more ATP. The content of most amino acids, such as L-isoleucine, L-tryptophan and L-citrulline, increased. In addition, phytoalexins, such as maackiain, nobiletin, vasicin, arachidonic acid, and JA-Ile, accumulated in M. micrantha. A total of 4978 differentially expressed genes were identified in M. micrantha infected by P. spegazzinii. Many key genes of M. micrantha in the PTI (pattern-triggered immunity) and ETI (effector-triggered immunity) pathways showed significantly higher expression under P. spegazzinii infection. Through these reactions, M. micrantha is able to resist the infection of P. spegazzinii and maintain its growth. These results are helpful for us to understand the changes in metabolites and gene expression in M. micrantha after being infected by P. spegazzinii. Our results can provide a theoretical basis for weakening the defense response of M. micrantha to P. spegazzinii, and for P. spegazzinii as a long-term biological control agent of M. micrantha.

Effects of Acute Hypoxic Stress on Physiological and Hepatic Metabolic Responses of Triploid Rainbow Trout (Oncorhynchus mykiss)

This experiment simulated the hypoxic environment caused by actual production operations in fish farming (i.e., catching, gathering, transferring, and weighting) to study the effects of acute hypoxic conditions on the physiological and metabolic responses of triploid rainbow trout (O. mykiss). Two groups of fish weighting 590 g were sampled in the normoxia group (dissolved oxygen above 7 mg/L) and hypoxia group (dissolved oxygen ranged from 2 to 5 mg/L for 10 min). The results showed that 1) regarding stress response, hypoxia increased plasma levels of cortisol, heat shock protein 70 (HSP-70), lysozyme, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and creatine phosphokinase (CPK); induced the expression of hepatic genes encoding nuclear factor erythroid 2 related factor 2 (Nrf2), interferon γ (IFN-γ) and interleukin-1β (IL-1β). 2) Regarding metabolism response, hypoxia increased plasma levels of globulin (GLOB), glucose (GLU), triglyceride (TG) and lactate dehydrogenase (LDH); upregulated the hepatic gene expression of phosphoenolpyruvate carboxykinase, (PEPCK), pyruvate dehydrogenase kinase (PDK1), acetyl-CoA carboxylase (ACC) and acetyl-CoA oxidase (ACO); downregulated the hepatic gene expression of carnitine palmitoyl transferase 1 (CPT1); and unchanged the expression of hepatic genes in glycolysis and autophagy. 3) In response to hypoxia-inducible factors (HIFs), the hepatic HIF-2α gene was activated in the hypoxia group, but HIF-1α gene expression remained unchanged. Thus, during acute hypoxic stress, triploid rainbow trout were in a defensive state, with an enhanced immune response and altered antioxidant status. Additionally, the hepatic mitochondrial oxidation of glucose- and lipid-derived carbon in trout was suppressed, and hepatic gluconeogenesis and lipid synthesis were activated, which might be regulated by the HIF-2α pathway.

Hypoxia stress affects the physiological responses, apoptosis and innate immunity of Kuruma shrimp, Marsupenaeus japonicus

For commercial aquatic animals, hypoxia phenomenon often occurs in live transport and aquaculture. In previous studies, much interest has been focused on antioxidant enzyme activities and could not present the complexities. The multifaceted responses, especially considering physiological indexes, histological structure, cell apoptosis, and immune pathways, are still unknown. In this study, we investigated the comprehensive hypoxic responses of Marsupenaeus japonicus. The results showed that the physiological indexes showed time-dependent changes upon hypoxia stress. Hypoxia stress led to significant tissue damage and cell apoptosis in the gill and hepatopancreas. Compared with the control group, the apoptosis index (AI) of the 12 h hypoxic treatment increased significantly (p < 0.05) in the gills and hepatopancreas. Comparative transcriptome analysis identified 900 and 1400 differentially expressed genes (DEGs) in the gill and hepatopancreas, respectively. Several DEGs were related to the lysosome, glycolysis/gluconeogenesis, citrate cycle, and apoptosis, and seven of them were validated using quantitative real-time PCR. This study provided valuable clues to understanding the mechanisms underlying the hypoxic responses of M. japonicus.

Mapping the Energetic Costs of Free-Swimming Gilthead Sea Bream (Sparus aurata), a Key Species in European Marine Aquaculture

Simple Summary

Assessment of the energetic costs of different living activities is of primary interest among fish biologists. However, assessing energy expenditure in free-swimming fish is challenging owing to the difficulty of performing such measurements in the field. Therefore, the use of implant fish with sensors that transmit signals that serve as a proxy for energy expenditure is a promising method to counter these limitations, allowing remote monitoring in tagged fish. The aim of this study was to correlate the acceleration recorded by the tag with the activities of the red and white muscles and the oxygen consumption rate (MO₂), which could serve as a proxy for energy expenditure, in gilthead sea bream (Sparus aurata), a key species in European marine aquaculture. The acceleration recorded by the tag was successfully correlated with MO₂. Additionally, through electromyographic analyses, we determined the activities of the red and white muscles, which are indicative of the contributions of aerobic and anaerobic metabolisms during swimming. Finally, the tag implantation did not affect the swimming performance, metabolic traits, and swimming efficiency of the sea bream. By obtaining insights into both aerobic and anaerobic metabolisms, sensor mapping with physiological indicators may be useful for the purposes of aquaculture health/welfare remote monitoring of gilthead sea bream.

Abstract

Measurement of metabolic rates provides a valuable proxy for the energetic costs of different living activities. However, such measurements are not easy to perform in free-swimming fish. Therefore, mapping acceleration from accelerometer tags with oxygen consumption rates (MO₂) is a promising method to counter these limitations and could represent a tool for remotely estimating MO₂ in aquaculture environments. In this study, we monitored the swimming performance and MO₂ of 79 gilthead sea bream (Sparus aurata; weight range, 219–971 g) during a critical swimming test. Among all the fish challenged, 27 were implanted with electromyography (EMG) electrodes, and 27 were implanted with accelerometer tags to monitor the activation pattern of the red/white muscles during swimming. Additionally, we correlated the acceleration recorded by the tag with the MO₂. Overall, we found no significant differences in swimming performance, metabolic traits, and swimming efficiency between the tagged and untagged fish. The acceleration recorded by the tag was successfully correlated with MO₂. Additionally, through EMG analyses, we determined the activities of the red and white muscles, which are indicative of the contributions of aerobic and anaerobic metabolisms until reaching critical swimming speed. By obtaining insights into both aerobic and anaerobic metabolisms, sensor mapping with physiological data may be useful for the purposes of aquaculture health/welfare remote monitoring of the gilthead sea bream, a key species in European marine aquaculture.

Deoxygenation reduces growth rates and increases assimilation of essential trace metals in gilthead seabream (Sparus aurata)

The widespread decline in oceanic dissolved oxygen (DO), known as deoxygenation, is a threat to many marine ecosystems, and fish are considered one of the more vulnerable marine organisms. While food intake and growth rates in some fish can be reduced under hypoxic conditions (DO ~ 60 μmol kg^-1), the dietary transfer of essential metals remains unclear. In this context, we investigated the influence of DO on the dietary acquisition of two essential metals (Zn and Mn) in the commercially important gilthead seabream (Sparus aurata) using radiotracer techniques. Fish were exposed to variable DO conditions (normoxia 100% DO, mild-hypoxia 60% DO, and hypoxia 30% DO), and fed a single radiolabeled food ration containing known activities of ⁵⁴Mn and ⁶⁵Zn. Depuration and assimilation mechanisms under these conditions were followed for 19 d. Based on whole body activity after the radio-feeding, food consumption tended to decrease with decreasing oxygen, which likely caused the significantly reduced growth (- 25%) observed at 30% DO after 19 d. While there was an apparent reduction in food consumption with decreasing DO, there was also significantly higher essential metal assimilation with hypoxic conditions. The proportion of ⁶⁵Zn remaining was significantly higher (~60%) at both low DO levels after 24 h and 19 d while ⁵⁴Mn was only significantly higher (27%) at the lowest DO after 19 d, revealing element specific effects. These results suggest that under hypoxic conditions, stressed teleost fish may allocate energy away from growth and towards other strategic processes that involve assimilation of essential metals.

Transcriptomic profiling of Gh/Igf system reveals a prompted tissue-specific differentiation and novel hypoxia responsive genes in gilthead sea bream

A customized PCR-array was used for the simultaneous gene expression of the Gh/Igf system and related markers of muscle growth, and lipid and energy metabolism during early life stages of gilthead sea bream (60–127 days posthatching). Also, transcriptional reprogramming by mild hypoxia was assessed in fingerling fish with different history trajectories on O₂ availability during the same time window. In normoxic fish, the expression of almost all the genes in the array varied over time with a prompted liver and muscle tissue-specific differentiation, which also revealed temporal changes in the relative expression of markers of the full gilthead sea bream repertoire of Gh receptors, Igfs and Igf-binding proteins. Results supported a different contribution through development of ghr and igf subtypes on the type of action of GH via systemic or direct effects at the local tissue level. This was extensive to Igfbp1/2/4 and Igfbp3/5/6 clades that clearly evolved through development as hepatic and muscle Igfbp subtypes, respectively. This trade-off is however very plastic to cope changes in the environment, and ghr1 and igfbp1/3/4/5 emerged as hypoxic imprinting genes during critical early developmental windows leading to recognize individuals with different history trajectories of oxygen availability and metabolic capabilities later in life.

Function of Chick Subcutaneous Adipose Tissue During the Embryonic and Posthatch Period

Since excess abdominal fat is one of the main problems in the broiler industry for the development of modern broiler and layer industry, the importance of subcutaneous adipose tissue has been neglected. However, chick subcutaneous adipose tissue appeared earlier than abdominal adipose tissue and more than abdominal adipose tissue. Despite a wealth of data, detailed information is lacking about the development and function of chick subcutaneous adipose tissue during the embryonic and posthatch period. Therefore, the objective of the current study was to determine the developmental changes of adipocyte differentiation, lipid synthesis, lipolysis, fatty acid β-oxidation, and lipid contents from E12 to D9.5. The results showed that subcutaneous adipose tissue was another important energy supply tissue during the posthatch period. In this stage, the mitochondrial copy number and fatty acid β-oxidation level significantly increased. It revealed that chick subcutaneous adipose tissue not only has the function of energy supply by lipidolysis but also performs the same function as brown adipose tissue to some extent, despite that the brown adipose tissue does not exist in birds. In addition, this finding improved the theory of energy supply in the embryonic and posthatch period and might provide theoretical basis on physiological characteristics of lipid metabolism in chicks.

Targeting the Mild-Hypoxia Driving Force for Metabolic and Muscle Transcriptional Reprogramming of Gilthead Sea Bream (Sparus aurata) Juveniles

Simple Summary

Reduced oxygen availability generates a number of adaptive features across all the animal kingdom, and the goal of this study was targeting the mild-hypoxia driving force for metabolic and muscle transcriptional reprogramming of gilthead sea bream juveniles. Attention was focused on blood metabolic and muscle transcriptomic landmarks before and after exhaustive exercise. Our results after mild-hypoxia conditioning highlighted an increased contribution of lipid metabolism to whole energy supply to preserve the aerobic energy production, a better swimming performance regardless of changes in feed intake, as well as reduced protein turnover and improved anaerobic fitness with the restoration of normoxia.

Abstract

On-growing juveniles of gilthead sea bream were acclimated for 45 days to mild-hypoxia (M-HYP, 40–60% O₂ saturation), whereas normoxic fish (85–90% O₂ saturation) constituted two different groups, depending on if they were fed to visual satiety (control fish) or pair-fed to M-HYP fish. Following the hypoxia conditioning period, all fish were maintained in normoxia and continued to be fed until visual satiation for 3 weeks. The time course of hypoxia-induced changes was assessed by changes in blood metabolic landmarks and muscle transcriptomics before and after exhaustive exercise in a swim tunnel respirometer. In M-HYP fish, our results highlighted a higher contribution of aerobic metabolism to whole energy supply, shifting towards a higher anaerobic fitness following normoxia restoration. Despite these changes in substrate preference, M-HYP fish shared a persistent improvement in swimming performance with a higher critical speed at exercise exhaustion. The machinery of muscle contraction and protein synthesis and breakdown was also largely altered by mild-hypoxia conditioning, contributing this metabolic re-adjustment to the positive regulation of locomotion and to the catch-up growth response during the normoxia recovery period. Altogether, these results reinforce the presence of large phenotypic plasticity in gilthead sea bream, and highlights mild-hypoxia as a promising prophylactic measure to prepare these fish for predictable stressful events.

Blood Will Tell: What Hematological Analyses Can Reveal About Fish Welfare

Blood analyses provide substantial information about the physiological aspects of animal welfare assessment, including the activation status of the neuroendocrine and immune system, acute and long-term impacts due to adverse husbandry conditions, potential diseases, and genetic predispositions. However, fish blood is still not routinely analyzed in research or aquaculture for the assessment of health and/or welfare. Over the years, the investigative techniques have evolved from antibody-based or PCR-based single-parameter analyses to now include transcriptomic, metabolomic, and proteomic approaches and from hematological observations to fluorescence-activated blood cell sorting in high-throughput modes. The range of testing techniques established for blood is now broader than for any other biogenic test material. Evaluation of the particular characteristics of fish blood, such as its cell composition, the nucleation of distinct blood cells, or the multiple isoforms of certain immune factors, requires adapted protocols and careful attention to the experimental designs and interpretation of the data. Analyses of fish blood can provide an integrated picture of the endocrine, immunological, reproductive, and genetic functions under defined environmental conditions and treatments. Therefore, the scarcity of high-throughput approaches using fish blood as a test material for fish physiology studies is surprising. This review summarizes the wide range of techniques that allow monitoring of informative fish blood parameters that are modulated by different stressors, conditions, and/or treatments. We provide a compact overview of several simple plasma tests and of multiparametric analyses of fish blood, and we discuss their potential use in the assessment of fish welfare and pathologies.

Effects of genetics and early-life mild hypoxia on size variation in farmed gilthead sea bream (Sparus aurata)

The present study evaluated, in an 18-month gilthead sea bream trial, the time course effects of genetics on individual size variation and growth compensation processes in families selected by heritable growth in the PROGENSA^® breeding program. Families categorized as fast, intermediate, and slow growing had different growth trajectories with a more continuous growth in fast growth families. This feature was coincident with a reduced size variation at the beginning of the trial that clustered together the half-sib families sharing the same father. Regression analysis evidenced that the magnitude of compensatory growth was proportional to the initial size variation with no rescaling of families at this stage. By contrast, the finishing growth depensation process can mask, at least partially, the previous size convergence. This reflects the different contribution across the production cycle of genetics in growth. How early-life experiences affect growth compensation at juvenile stages was also evaluated in a separate cohort, and intriguingly, a first mild-hypoxia pulse at 60-81 days post-hatching (dph) increased survival rates by 10%, preventing growth impairment when fish were exposed to a second hypoxia episode (112-127 dph). The early hypoxia experience did not have a negative impact on growth compensatory processes at juvenile stages. By contrast, a diminished capacity for growth compensation was found with repeated or late hypoxia experiences. All this reinforces the use of size variation as a main criterion for improving intensive fish farming and selective breeding.

Yucca schidigera Usage for Healthy Aquatic Animals: Potential Roles for Sustainability

Simple Summary

This review presents an updated and exclusive collection of results about yucca’s beneficial effects as phytogenic additives for clean aquaculture activity. The overall performances of aquatic organisms treated with yucca as dietary additives of water cleaners encourage performing further studies to prove its mode of action based on biochemical and biological techniques.

Abstract

In modern aquaculture systems, farmers are increasing the stocking capacity of aquatic organisms to develop the yield and maximize water resources utilization. However, the accumulation of ammonia in fishponds regularly occurs in intensive aquaculture systems, resulting in reduced growth rates and poor health conditions. The inclusion of yucca extract is recognized as a practical solution for adsorbing the waterborne ammonia. Yucca has abundant amounts of polyphenolics, steroidal saponins, and resveratrol and can be used as a solution or as a powder. In this context, this review aimed to investigate the possible regulatory roles of yucca extract on aquatic animals’ performances. Concurrently, the feed utilization, growth performance, and physiological status of aquatic species can be improved. Additionally, the yucca application resulted in enhancing the antioxidative, immunological, and anti-inflammatory responses in several aquatic animals. Exclusively, the present review proposed a protective solution through the application of yucca extract in the aquafeed and rearing water of aquatic animals suffering from ammonia accumulation. Furthermore, it shows how yucca could enhance the growth, survival rates, blood biochemical quality, immunological indices, and the antioxidative capacity of aquatic animals in light of the relevant published data.

GHRH-SST-GH-IGF axis regulates crosstalk between growth and immunity in rainbow trout (Oncorhynchus mykiss) infected with Vibrio anguillarum

An energy trade-off is existed between immunological competence and growth. The axis of growth hormone releasing hormone, somatostatin, growth hormone, insulin-like growth factor (GHRH-SST-GH-IGF axis) regulates growth performances and immune competences in rainbow trout (Oncorhynchus mykiss). The salmonid-specific whole genome duplication event is known to result in duplicated copies of several key genes in GHRH-SST-GH-IGF axis. In this study, we evaluated the physiological functions of GHRH-SST-GH-IGF axis in regulating crosstalk between growth and immunity. Based on principal components analysis (PCA), we observed the overall expression profiles of GHRH-SST-GH-IGF axis were significantly altered by Vibrio anguillarum infection. Trout challenged with Vibrio anguillarum showed down-regulated igf1s subtypes and up-regulated igfbp1a1. The brain sst genes (sst1a, sst1b, sst3b and sst5) and igfpbs genes (igfbp4s and igfbp5b2) were significantly affected by V. anguillarum infection, while the igfbp4s, igfbp5s, igfbp6s and igf2bps genes showed significant changes in peripheral immune tissues in response to V. anguillarum infection. Gene enrichment analyses showed functional and signaling pathways associated with apoptosis (such as p53, HIF-1 or FoxO signaling) were activated. We further proposed a possible model that describes the IGF and IGFBPs-regulated interaction between cell growth and programmed death. Our study provided new insights into the physiological functions and potentially regulatory mechanisms of the GHRH-SST-GH-IGF axis, indicating the pleiotropic effects of GHRH-SST-GH-IGF axis in regulating crosstalk between growth and immunity in trout.

The Relationship between the Expression of Fatty Acyl Desaturase 2 (fads2) Gene in Peripheral Blood Cells (PBCs) and Liver in Gilthead Seabream, Sparus aurata Broodstock Fed a Low n-3 LC-PUFA Diet

The principle aim of this study is to elucidate the relationship between the fatty acid desaturase 2 gene (fads2) expression pattern in peripheral blood cells (PBCs) and liver of gilthead seabream (GSB), Sparus aurata broodstock in order to determine the possible use of fads2 expression as a potential biomarker for the selection of broodstock. This selection could be utilized for breeding programs aiming to improve reproduction, health, and nutritional status. Passive Integrated Transponder (PIT)-tagged GSB broodstock (Male-1.22 ± 0.20 kg; 44.8 ± 2 cm and female-2.36 ± 0.64 kg; 55.1 cm) were fed a diet containing low levels of fish meal and fish oil (EPA 2.5; DHA 1.7 and n-3 LC-PUFA 4.6% TFA) for one month. After the feeding period, fads2 expression in PBCs and liver of both male and female broodstock were highly significantly correlated (r = 0.89; p < 0.001). Additionally, in male broodstock, liver fads2 expression was significantly correlated (p < 0.05) to liver contents in 16:0 (r = 0.95; p = 0.04) and total saturates (r = 0.97; p = 0.03) as well as to 20:3n–6/20:2n–6 (r = 0.98; p = 0.02) a Fads2 product/precursor ratio. Overall, we found a positive and significant correlation between fads2 expression levels in the PBCs and liver of GSB broodstock. PBCs fads2 expression levels indicate a strong potential for utilization as a non-invasive method to select animals having increased fatty acid bioconversion capability, better able to deal with diets free of fish meal and fish oil.

Environmental hypoxia causes growth retardation, osteoclast differentiation and calcium dyshomeostasis in juvenile rainbow trout (Oncorhynchus mykiss)

Hypoxia generally refers to a dissolved oxygen (DO) level that is less than 2-3 mg/L. With ongoing global warming and environment pollution, environmental or geological studies showed hypoxia frequently occurs in global aquatic systems including ocean, river, estuaries and coasts. A preliminary study was performed to evaluate hypoxia tolerant of rainbow trout (Oncorhynchus mykiss) with parameters of mortality, behavior, endocrine and metabolite, identifying three DO levels including normoxia (Ctrl, 7.0 mg/L), non-lethal hypoxia (NH, 4.5 mg/L) and lethal hypoxia (LH, 3.0 mg/L). Furthermore, trout was treated by Ctrl, NH and LH for six hours to mimic the acute hypoxia in wild and/or farming conditions. A significantly higher mortality was observed in LH group. Trout of NH and LH showed stressful responses with unnormal swimming, increased serum cortisol and up-regulated gill hif1α transcription. Despite trout of NH and LH increased the oxygen delivery abilities by increasing the serum hemoglobin levels, the anerobic metabolism were inevitably observed with increased lactate. This study also showed a prolonged influence of NH and LH on growth after 30-days' recovery. Based on RNA-Seq data, different expression genes (DEGs) associated with stress, apoptosis, antioxidant, chaperone, growth, calcium and vitamin D metabolism were identified. Enrichment analysis showed DEGs were clustered in osteoclast differentiation, apoptosis and intracellular signaling transduction pathways. Results further showed NH and LH significantly decreased bone calcium content and disrupted the growth hormone-insulin-like growth factor (GH-IGF) axis. Our study might contribute to a better understanding of the effects of hypoxia on rainbow trout.

Stearoyl-CoA desaturase (scd1a) is epigenetically regulated by broodstock nutrition in gilthead sea bream (Sparus aurata)

The aim of this study was to generate new knowledge on fish epigenetics, assessing the effects of linolenic acid (ALA) conditioning of broodstock in the offspring of the marine fish Sparus aurata. Attention was focused on gene organization, methylation signatures and gene expression patterns of fatty acid desaturase 2 (fads2) and stearoyl-CoA desaturase 1a (scd1a). Blat searches in the genomic IATS-CSIC database (www.nutrigroup-iats.org/seabreamdb) highlighted a conserved exon-intron organization, a conserved PUFA response region, and CG islands at the promoter regions of each gene. The analysed CpG positions in the fads2 promoter were mostly hypomethylated and refractory to broodstock nutrition. The same response was achieved after conditioning of juvenile fish to low water oxygen concentrations, thus methylation susceptibility at individual CpG sites seems to be stringently regulated in fish of different origin and growth trajectories. Conversely, the scd1a promoter was responsive to broodstock nutrition and the offspring of parents fed the ALA-rich diet shared an increased DNA-methylation, mainly in CpG sites neighbouring SP1 and HNF4α binding sites. Cytosine methylation at these sites correlated inversely with the hepatic scd1a expression of the offspring. Co-expression analyses supported that the HNF4α-dependent regulation of scd1a is affected by DNA methylation. The phenotypic output is a regulated liver fat deposition through changes in scd1 expression, which would also allow the preservation of fatty acid unsaturation levels in fish fed reduced levels of n-3 LC-PUFA. Collectively, these findings reveal a reliable mechanism by which parent's nutrition can shape scd1a gene expression in the fish offspring.

Microarray and metabolome analysis of hepatic response to fasting and subsequent refeeding in zebrafish (Danio rerio)

Background

Compensatory growth refers to the phenomenon in which organisms grow faster after the improvement of an adverse environment and is thought to be an adaptive evolution to cope with the alleviation of the hostile environment. Many fish have the capacity for compensatory growth, but the underlying cellular mechanisms remain unclear. In the present study, microarray and nontargeted metabolomics were performed to characterize the transcriptome and metabolome of zebrafish liver during compensatory growth.

Results

Zebrafish could regain the weight they lost during 3 weeks of fasting and reach a final weight similar to that of fish fed ad libitum when refed for 15 days. When refeeding for 3 days, the liver displayed hyperplasia accompanied with decreased triglyceride contents and increased glycogen contents. The microarray results showed that when food was resupplied for 3 days, the liver TCA cycle (Tricarboxylic acid cycle) and oxidative phosphorylation processes were upregulated, while DNA replication and repair, as well as proteasome assembly were also activated. Integration of transcriptome and metabolome data highlighted transcriptionally driven alterations in metabolism during compensatory growth, such as altered glycolysis and lipid metabolism activities. The metabolome data also implied the participation of amino acid metabolism during compensatory growth in zebrafish liver.

Conclusion

Our study provides a global resource for metabolic adaptations and their transcriptional regulation during refeeding in zebrafish liver. This study represents a first step towards understanding of the impact of metabolism on compensatory growth and will potentially aid in understanding the molecular mechanism associated with compensatory growth.

Effects of long-term crowding stress on neuro-endocrine-immune network of rainbow trout (Oncorhynchus mykiss)

Low levels of stresses cause eustress while high stressful situations result in distress. Female rainbow trout (Oncorhynchus mykiss) was reared under crowded conditions to mimic the stressful environment of intensive fishery production. Trout was stocked for 300 days with initial densities of 4.6 ± 0.02 (final: 31.1 ± 0.62), 6.6 ± 0.03 (final: 40.6 ± 0.77), and 8.6 ± 0.04 (final: 49.3 ± 1.09) kg/m³ as SD1, SD2 and SD3. We assessed molecular, cellular and organismal parameters to understand the flexibility of neuro-endocrine-immune network during stress. Trout with higher initial density (SD3) displayed the slightly activated hypothalamus-pituitary-interrenal (HPI) axis with positively increased antioxidant enzyme activities and anti-inflammatory cytokine transcriptions on day 60 or 120. These results indicated that low level of stress was capable of exerting eustress by activating neuro-endocrine-immune network with beneficial adaptation. Transition from eustress to distress was induced by the increased intensity and duration of crowding stress on day 240 and 300. The prolonged activation of HPI axis resulted in suppressed growth hormone-insulin-like growth factor (GH-IGF) axis, up-regulated cytokine transcriptions and severe reactive oxygen species stress. Stress means reset of neuro-endocrine-immune network with energy expenditure and redistribution. Digestive ability of trout with distress was also inhibited on day 240 and 300, indicating a decreased total energy supplement and energy distribution for functions are not necessary for surviving such as growth and reproduction. Consequently, we observed the dyshomeostasis of energy balance and neuro-endocrine-immune network of trout during long-term crowding conditions.