Asian Aquaculture Research Articles

Antibiotic residues from aquaculture farms and their ecological risks in Southeast Asia: a case study from Malaysia

ABSTRACT Background and Objectives: One major source of antibiotic contamination in the sea is from aquaculture. We monitored the concentration of commonly used antibiotic classes and antibiotic resistance genes (tet(M), sul1, sul2 and sul3) in aquaculture farms in Peninsular Malaysia. Methods: Antibiotic residues and resistance genes were quantified using high-performance liquid chromatography and real-time PCR respectively. Risk quotients in European technical guidance document on risk assessment was used to assess the potential environmental risk. Results: We detected 23 antibiotics with tetracyclines, sulfonamides and quinolones were the most frequently detected classes, indicating a wide distribution of antibiotics in Malaysian aquaculture farms. The dendrogram and heatmap revealed three groups of antibiotic concentration patterns but with no differences in the types of antibiotics usage among aquaculture farms. The ARGs (10−3 copies/16S) were detected in >90% of the sites except for sul3. Ciprofloxacin, enrofloxacin, norfloxacin and lincomycin posed risks to cyanobacteria and algae in Kelantan, Perak and Pahang. Conclusion: Relative to Asian aquaculture farms, the residues detected here were at low or moderate levels except for quinolones. This study will be useful to develop effective management of aquaculture wastewater in order to mitigate antibiotic pollution and transmission of ARGs to humans through the food chain.

Aerator energy use in shrimp farming and means for improvement

AbstractEstimates of aeration energy use in shrimp farming varied from 11.4 to 41.6 GJ/t shrimp (average = 19.8 GJ/t). Several opportunities for reducing energy use in aeration are available. Many farms adopt an excessive yield to installed aeration capacity ratio. Moreover, the proportion of installed aerator capacity in use and duration of aerator operation per day are often more than necessary during the initial two‐thirds of grow‐out, because adjustment is not made for the quantity of shrimp biomass. Farm‐made, long‐arm aerators used in Asia have several features leading to energy inefficiency and could be replaced by more efficient factory‐made, long‐arm aerators. Asian aquaculture aerator manufacturers should redesign aerators to include design features shown in research to improve efficiency. Dissolved oxygen concentration monitoring essential for verification of aeration performance is seldom performed by shrimp farmers. With good aeration technique, energy use for aeration should not exceed 10–15 GJ/t shrimp.

Identification of Pathogenic Bacteria from Diseased Thai Pangas Pangasius hypophthalmus with Their Sensitivity to Antibiotics

Thai Pangas (Pangasiaus hypophthalmus) has been emerging as an economically very important species due their faster growth, year round production and high productivity in South-East Asian aquaculture. It has good market value as a food fish due to its good taste and deliciousness with high protein, minerals and fat content. It is also popular as a game fish.
 Aims: The present study was conducted to identify bacterial pathogens in diseased P. hypophthalmus and evaluate their sensitivity to antibiotics.
 Methodology: To identify the causativeagent of diseased fish pure culture of bacteria using slant and streak plate techniques and different biochemical tests such as Gram’s Staining, Motility Test, Sugar Fermentation Test, MR-VP test, Indole Test etc. were performed. To assess the sensitivity of the isolated bacteria to antibiotics five antibiotics disks i.e. Ciprofloxacin (5μg), Azithromycin (15μg), Ampicillin/Sulbactam (20μg), Tetracycline (30μg) and Erythromycin (15μg) were used.
 Results: Three pathogenic bacteria i.e. Aeromonas hydrophila, Edwardsiella ictaluri and Pseudomonas sp. were identified in the studied diseased fish. Only Pseudomonas sp. were identified from Fresh fish. E. ictaluri was found only in diseased pangas which was the causative agent for thedisease, Bacillary Necrosis. The results of the antibiotic sensitivity test showed multi-resistances of the identified bacteria to the tested antibiotics. The identified bacteria were 100% sensitive to Ciprofloxacin (5μg), intermediate to Azithromycin (15μg) and Tetracycline (30μg), but resistant to Erythromycin (15μg) and Ampicilin/Sulbactam (20μg).
 Conclusion: Ciprofloxacin (5µg) could be used to control bacillary necrosis disease in Thai pangas. The results of this study will be helpful to the fish farmers for the management of bacterial diseases in fish.

A T3SS Regulator Mutant of Vibrio alginolyticus Affects Antibiotic Susceptibilities and Provides Significant Protection to Danio rerio as a Live Attenuated Vaccine.

Vibrio alginolyticus is a major cause of Vibriosis in farmed marine aquatic animals and has caused large economic losses to the Asian aquaculture industry in recent years. Therefore, it is necessary to control V. alginolyticus effectively. The virulence mechanism of V. alginolyticus, the Type III secretion system (T3SS), is closely related to its pathogenicity. In this study, the T3SS gene tyeA was cloned from V. alginolyticus wild-type strain HY9901 and the results showed that the deduced amino acid sequence of V. alginolyticus tyeA shared 75–83% homology with other Vibrio spp. The mutant strain HY9901ΔtyeA was constructed by Overlap-PCR and homologous recombination techniques. The HY9901ΔtyeA mutant exhibited an attenuated swarming phenotype and an ~40-fold reduction in virulence to zebrafish. However, the HY9901ΔtyeA mutant showed no difference in growth, biofilm formation and ECPase activity. Antibiotic susceptibility test was observed that wild and mutant strains were extremely susceptible to Amikacin, Minocycline, Gentamicin, Cefperazone; and resistant to oxacillin, clindamycin, ceftazidime. In contrast wild strains are sensitive to tetracycline, chloramphenicol, kanamycin, doxycycline, while mutant strains are resistant to them. qRT-PCR was employed to analyze the transcription levels of T3SS-related genes, the results showed that compared with HY9901 wild type, ΔtyeA had increased expression of vscL, vscK, vscO, vopS, vopN, vscN, and hop. Following vaccination with the mutant strain, zebrafish had significantly higher survival than controls following infection with the wild-type HY9901 (71.2% relative percent survival; RPS). Analysis of immune gene expression by qPCR showed that vaccination with HY9901ΔtyeA increased the expression of IgM, IL-1β, IL-6, and TNF-α in zebrafish. This study provides evidence of protective efficacy of a live attenuated vaccine targeting the T3SS of V. alginolyticus which may be facilitated by up-regulated pro-inflammatory and immunoglobulin-related genes.

Cloning and characterisation of type I interferon receptor 1 in orange-spotted grouper (Epinephelus coioides) for response to nodavirus infection

Grouper is known as a highly economical teleost species in the Asian aquaculture industry; however, intensive culture activities easily cause disease outbreak, especially viral disease. For the prevention of viral outbreaks, interferon (IFN) is among the major defence systems being studied in different species. Fish type I IFNs are known to possess antiviral properties similar to mammalian type I IFNs. In order to stimulate antiviral function, IFN will bind to its cognate receptor, the type I interferon receptor (IFNAR), composed of heterodimeric receptor subunits known as IFNAR1 and IFNΑR2. The binding of type I interferon to receptors assists in the transduction of signals from the external to internal environments of cells to activate biological responses. In order to study the function of IFN, we first need to understand IFN receptors. In this study, we cloned and identified IFNAR1 in orange-spotted grouper (osgIFNAR1) and noted the up-regulated mRNA expression of the receptor and downstream effectors in the head kidney cells with cytokine treatment. The transcriptional expression of osgIFNAR1, which is characterised using polyinosinic-polycytidylic acid (poly[I:C]) and lipopolysaccharide (LPS) treatments, indicated the involvement of osgIFNAR1 in the immune response of grouper. The subcellular localisation of osgIFNAR1 demonstrated scattering across the grouper cell. Viral infection showed the negative feedback regulation of osgIFNAR1 in grouper larvae. Further loss of function of IFNAR1 showed a decreased expression of the virus. This study reported the identification of osgIFNAR1 and characterisation of receptor sensitivity towards immunostimulants, cytokine response, and viral challenge in the interferon pathway of orange-spotted grouper and possible different role of the receptor in viral production. Together, these results provide a frontline report of the potential function of osgIFNAR1 in the innate immunity of teleost.

Construction of a high-density genetic map and mapping of growth related QTLs in the grass carp (Ctenopharyngodon idellus)

BackgroundGrass carp (Ctenopharyngodon idellus) are important species in Asian aquaculture. A draft genome for grass carp has already been published in 2015. However, there is still a requirement for a suitable genetic linkage map to arrange scaffolds on chromosomal frameworks. QTL analysis is a powerful tool to detect key locations for quantitative traits, especially in aquaculture. There no growth related QTLs of grass carp have been published yet. Even the growth trait is one of the focuses in grass carp culture.ResultsIn this study, a pair of distantly related parent grass carps and their 100 six-month-old full-sib offspring were used to construct a high-density genetic map with 6429 single nucleotide polymorphisms (SNPs) by 2b-RAD technology. The total length of the consensus map is 5553.43 cM with the average marker interval of 1.92 cM. The map has a good collinearity with both the grass carp draft genome and the zebrafish genome, and it assembled 89.91% of the draft genome to a chromosomal level. Additionally, according to the growth-related traits of progenies, 30 quantitative trait loci (QTLs), including 7 for body weight, 9 for body length, 5 for body height and 9 for total length, were identified in 16 locations on 5 linkage groups. The phenotypic variance explained for these QTLs varies from 13.4 to 21.6%. Finally, 17 genes located in these regions were considered to be growth-related because they either had functional mutations predicted from the resequencing data of the parents.ConclusionA high density genetic linkage map of grass carp was built and it assembled the draft genome to a chromosomal level. Thirty growth related QTLs were detected. After the cross analysis of Parents resequencing data, 17 candidate genes were obtained for further researches.

The Responsible Seafood Tool (RESET): Empowering businesses in Asia to source seafood more responsibly

The current situation observed in the seafood industry demonstrates that responsible and certified seafood produced in Asia as well as other developing regions is often exported out to Western markets such as Europe and the US, due to a higher demand and higher willingness to pay. This renders responsible and certified seafood to be shipped out of Asia and results in a market where responsible and certified seafood is systematically underrepresented. Hence, the lack of supply of responsible seafood from regional sources has hindered companies’ efforts to source responsibly, despite a commitment to do so. With Asia’s increasing disposable income and growing awareness by consumers for responsible and certified seafood, greater opportunities can be leveraged upon by World Wide Fund for Nature (WWF) to increase the supply and demand of responsible seafood in the region. The Responsible Seafood Tool (RESET) is developed as WWF believes that there is opportunity for change in empowering businesses in Asia to source more responsibly, particularly for a local favourite - seafood. Responsible seafood sourcing helps to reduce negative consequences to the environment, in the form of biodiversity loss, seascape degradation, and resource depletion, as well as to reduce lost livelihoods displaced by depleted fishstock or polluted landscapes and seascapes. The tool seeks to lower the barriers for businesses to source for responsible seafood, and to directly mobilize improved management and performance of fisheries and aquaculture in Asia. In a nutshell, RESET aims to provide easy access to the supply of responsible seafood for interested buyers, while also supporting Asian aquaculture and fisheries by providing business incentives for certification. Seafood buyers enjoy the access of a variety of responsible seafood from Asia, at the same time, they enable WWF to propel responsible seafood producers along their journey to achieve Aqualculture Stewardship Council (ASC) or Marine Stewardship Council (MSC) certification.

Effects of dietary α-linolenic acid/linoleic acid ratio on growth performance, tissue fatty acid profile, serum metabolites and Δ6 fad and elovl5 gene expression in silver barb (Puntius gonionotus).

Silver barb (Puntius gonionotus) is a medium-sized carp that is promising for freshwater aquaculture in Asia. This study's aim was to investigate the ideal dietary α-linolenic acid (ALA): linoleic acid (LA) ratio for maximizing long-chain polyunsaturated fatty acid (LC-PUFA) synthesis and their deposition in the muscle of silver barb, as that of fish oil based control diet. Fish (with an initial body weight of 11.07 ± 0.12 g) were fed for 60 days with five experimental iso-proteinous, iso-lipidic, and iso-caloric diets, supplemented with linseed oil and peanut oil at varying levels to obtain ALA:LA ratios of 0.35, 0.51, 0.91, 2.04, 2.66. A control diet was prepared by supplementing fish oil. The dietary ALA:LA ratio did not influence the growth performance of fish. With increased dietary ALA:LA ratios, LA content decreased and ALA content increased in the muscle and liver of silver barb. The n-3 LC-PUFA level in muscle and liver was not influenced by feeding different ratios of ALA:LA, whereas n-6 LC-PUFA was decreased in the muscle and increased in the liver with increased dietary ALA:LA ratios. Increasing dietary ALA:LA ratio increased the Δ6fad and elovl5mRNA expression in the liver, muscle, brain, and intestinal tissues of silver barbs. Silver barb possess the ability to elongate and desaturate ALA and LA to their end products EPA and DHA. The highest level expression of Δ6 fad and elovl5 mRNA at the dietary ALA:LA ratio of 2.66 suggests greater affinity of these enzymes towards ALA than LA in silver barb. © 2019 Society of Chemical Industry.

A review of reported seaweed diseases and pests in aquaculture in Asia

AbstractSeaweeds have been used as a food for centuries in Asia and are increasingly exploited as a source for dietary supplements, animal feed, chemicals, and biofuels. In recent years, there has been an increase in the prevalence of diseases and pests in these aquaculture crops, with a subsequent reduction in their quantity and commercial value. In this article, we review diseases that have been reported in the scientific literature for species of red and brown seaweeds. We have focused on the major seaweed crops grown in Asia, where much of this production is centered. We also provide information on disease management and biosecurity and some observations on future directions.

Estrogen suppresses bcl2 expression through dnmt1 in Japanese eel ovarian follicle.

Japanese eels are commercially valuable species in Asian aquaculture. This study evaluated whether salmon pituitary extract (SPE) or 17β-estradiol (E2) treatment can induce cytotoxic activity in eel ovarian follicles. Follicular cells died after exposure SPE for 24-h culture in an in vitro culture. Moreover, the E2 treatment also significantly reduced follicular cell counts. These results reveal that the inhibition of follicular cell numbers by SPE may occur through SPE-induced steroidogenesis. Results of a quantitative PCR analysis indicated that adding E2 to the culture decreased bcl2 and increased dnmt1 mRNA expression in Japanese eel follicular cells after 24 h. The results of a promoter assay revealed that E2 significantly increase dnmt1 promoter activity through estrogen receptor-binding site. An in silico analysis predicted several putative transcription factors targeting the bcl2 gene promoter region. Methylation of the bcl2 promoter accounted for the downregulation of bcl2 by E2-mediated dnmt1. The DNA methylation level of the bcl2 gene was significantly higher in E2-treated follicular cells than that in the control group. Finally, the E2-induced hypermethylation pattern of the bcl2 promoter and the reduction in follicular cell numbers were suppressed by adding an MTase inhibitor. Our findings demonstrate that estrogen has a negative effect on the reproductive system of female eels by regulating an epigenetic mechanism during artificial maturation.

Swimming in their own direction: Explaining domestic variation in homegrown sustainability governance for aquaculture in Asia

Agricultural commodity production in the Global South is accompanied by a range of social and environmental problems ranging from pollution and deforestation to labor rights violations. Accordingly, governments and non-state actors have responded through various governance initiatives aimed at promoting sustainable commodity production. While the existing literature focuses largely on transnational standards originating in the North, we investigate “homegrown” approaches in the South by asking: what explains variation in the design and features of sustainable commodity governance led by Southern actors? By comparing sustainable aquaculture governance in Thailand, Vietnam, and China, we derive a novel conceptualization of two distinct types of homegrown governance approaches – certification standards and capability-building programs – and suggest that the choice between the two is contingent on the supply of, and demand for, sustainable commodity governance. We find decisions by Southern governments to supply governance can lock in top-down approaches and exclude potentially more impactful bottom-up approaches. We therefore argue that the material resources and normative concerns of Southern governance entrepreneurs lead to different homegrown approaches. Our findings contribute theoretical insights to the literature on transnational governance interactions and practical observations about the utility of different approaches to sustainability concerns in the Global South.

Isolation, Characterization and Pathogenicity of Edwardsiella tarda a Causative Disease on Freshwater Fish in Yogyakarta

Edwarsiella tarda is a cosmopolitan bacterium and is a cause of Edwardsiellosis in various fish species. The bacterial infection causes large losses on aquaculture in Asia, especially Japan. This study was conducted to isolate and characterize E. tarda as causative disease in freshwater fishes, and to determine its pathogenicity to catfish (Pangasius sp.). Bacteria were isolated from kidney of diseased fishes on Tryptone Soya Agar medium. Identification was conducted based on morphological colonies, morphological cells and biochemical tests. Fulfillment of Koch Postulates was done by injecting bacteria intraperitoneally on 7-9 cm fishes at dose of 107 cfu/fish. Pathogenicity test was carried out by intraperitoneal injection at 104, 105, 106, and 107 cfu/fish to 7-9 cm-catfish (Pangasius sp.) and followed by observation of disease signs and mortality every six hours for 7 days. Pathogenicity was determined as Lethal Dosage (LD50) using Dragstedt Behrens method. In this research we have isolated three isolates E. tarda causing disease in fishes. The clinical signs of this disease were lose of pigmentation over the lession, swollen of stomach, haemorhage on fins , small cutaneous lesions, and necrotic on fins area. The LD50 of E. tarda isolate L2, L3, and N3 were 4.64 ± 0.35x105, 1.54 ± 0.07x105, and 1.13 ± 0.13x106 cfu/fish, respectively.

Description of a Natural Infection with Decapod Iridescent Virus 1 in Farmed Giant Freshwater Prawn, Macrobrachium rosenbergii.

Macrobrachium rosenbergii is a valuable freshwater prawn in Asian aquaculture. In recent years, a new symptom that was generally called “white head” has caused high mortality in M. rosenbergii farms in China. Samples of M. rosenbergii, M. nipponense, Procambarus clarkii, M. superbum, Penaeus vannamei, and Cladocera from a farm suffering from white head in Jiangsu Province were collected and analyzed in this study. Pathogen detection showed that all samples were positive for Decapod iridescent virus 1 (DIV1). Histopathological examination revealed dark eosinophilic inclusions and pyknosis in hematopoietic tissue, hepatopancreas, and gills of M. rosenbergii and M. nipponense. Blue signals of in situ digoxigenin-labeled loop-mediated isothermal amplification appeared in hematopoietic tissue, hemocytes, hepatopancreatic sinus, and antennal gland. Transmission electron microscopy of ultrathin sections showed a large number of DIV1 particles with a mean diameter about 157.9 nm. The virogenic stromata and budding virions were observed in hematopoietic cells. Quantitative detection with TaqMan probe based real-time PCR of different tissues in naturally infected M. rosenbergii showed that hematopoietic tissue contained the highest DIV1 load with a relative abundance of 25.4 ± 16.9%. Hepatopancreas and muscle contained the lowest DIV1 loads with relative abundances of 2.44 ± 1.24% and 2.44 ± 2.16%, respectively. The above results verified that DIV1 is the pathogen causing white head in M. rosenbergii. M. nipponense and Pr. clarkii are also species susceptible to DIV1.

Localization and tissue tropism of viral haemorrhagic septicemia virus (VHSV) in experimentally infected juvenile olive flounder, Paralichthys olivaceus: An in situ hybridization and immunohistochemical study

An insight on localization of viral pathogen is imperative to better understand the host-pathogen interaction. Previously, we developed an in-situ hybridization (RNA-ISH) assay to detect viral hemorrhagic septicemia virus (VHSV), an OIE reportable fish pathogen, in an in vitro model. Here, we utilized its potential and applicability in vivo to further our understanding about the localization and tissue tropism of VHSV in experimentally infected juvenile olive flounder (Paralichthys olivaceus), an economically important flatfish in Asian aquaculture. Two separate digoxigenin (DIG) labeled antisense RNA probes targeting a fragment of viral nucleoprotein (N) and glycoprotein (G) gene segments were employed to localize VHSV in five infected flounder tissues viz., kidney, spleen, heart, liver and brain. Further, immunohistochemistry (IHC) assay was also used to observe and substantiate the spatial localization of the viral particles using a monoclonal antibody (MAb) against the viral nucleoprotein (N). Following the RNA-ISH and IHC assays, VHSV localization was observed in different cells and areas of the tested tissues. The positive reaction in both the assays correlated with histopathological alterations confirming the presence of VHSV within the tested tissues. Information gained from the present study using both genome and protein based localization sheds light on viral tropism which can help to further elucidate VHSV pathogenesis in olive flounder.

Diagnosis and treatment of multi-species fish mortality attributed to Enteromyxum leei while in quarantine at a US aquarium.

Enteromyxum leei is an enteric myxozoan parasite of fish. This myxozoan has low host specificity and is the causative agent of myxozoan emaciation disease, known for heavy mortalities and significant financial losses within Mediterranean, Red Sea, and Asian aquaculture industries. The disease has rarely been documented within public aquaria and, to our knowledge, has never been confirmed within the USA. This case report describes an outbreak of E. leei in a population of mixed-species east African/Indo-Pacific marine fish undergoing quarantine at a public aquarium within the USA. Four of 16 different species of fish in the population, each of a different taxonomic family, were confirmed infected by the myxozoan through cloacal flush or intestinal wet mount cytology at necropsy. Clinical and histopathological findings in this case are similar to previous findings describing myxozoan emaciation disease, e.g. severe emaciation, cachexia, enteritis, and death. Sequence analysis of the 18S rDNA of intestinal samples from a powder blue tang Acanthurus leucosternon and an emperor angelfish Pomacanthus imperator confirmed the parasite to have 99-100% identity with other E. leei sequences. Spore morphology and ultrastructure were consistent with previous reports of E. leei. Treatment of clinically affected fish by oral administration of the coccidiostats amprolium and salinomycin led to reduction of mortalities and resolution of clinical signs. This case report highlights the importance of thorough examination and surveillance of fish during quarantine, particularly with respect to enteric myxozoans.

Embryonic, larval and juvenile development of the longfin batfish, Platax teira (Forsskål, 1775) under controlled conditions with special regard to mitigate cannibalism for larviculture

Longfin batfish Platax teira is one of the most important finfish species in Asian aquaculture. However, knowledge on early ontogeny and reproduction of this species in captivity are scarce and incomplete. In this study, the embryonic, larval and juvenile development of P. teira are described and illustrated for the first time. The effect of temperature (27, 30 and 33 °C) on hatching rate, yolk-sac volume and oil globule volume was demonstrated. Cannibalism control via aeration adjustment for the enhancement of larval survival was also examined. Fertilized eggs were spherical, buoyant and had a diameter of 1.29 ± 0.05 mm (mean ± SD). Embryonic development lasted 16 h at 26.2 °C. Newly hatched larvae were 2.81 ± 0.24 mm in total length (LT) with 24 myomeres and had an oil globule in the ventroposterior area of the yolk sac. Early larvae had xanthophores appeared all over the body, except for the tip of the notochord. Larvae completed yolk absorption within 3 days post hatching (dph) at 3.41 ± 0.11 mm LT. Larvae were fed initially on rotifers Brachionus ibericus, followed by Artemia nauplii and finally weaned onto an artificial diet. From 8 dph, the larger larvae (over 4 mm LT) began to exhibit cannibalistic behaviour. Transformation of larvae to the juvenile stage was completed at 23.80 ± 1.98 mm LT, all fins had the adult complement of rays and spines. A statistical model: Y = 2.4968e0.0786x, where Y is mean LT (mm) and X represents dph, explained 96.45% of variation in growth (P < 0.001, R2 = 0.9645). The hatching rate, yolk-sac volume and oil globule volume of newly hatched larvae were significantly (P < 0.05) decreased when the incubation temperature increased. Only 2–6% of embryos hatched at 33 °C, while the hatching rate was 63 ± 6% at 27 °C. Larvae reared in aeration rate of 300 mL min−1 attained the highest survival rate at 70.00 ± 7.20%, but remained significantly (P < 0.05) lower in cannibalism: 24.44 ± 4.16% compared with 66.67 ± 5.44% in 20 mL min−1. These results indicate that the optimal incubation temperature recommended is approximately at 27 °C, and aeration at 300 mL min −1 could enhance larval survival by reducing cannibalism.

Mycotoxins in Southeast Asian aquaculture: plant-based meals and finished feeds

The awareness of mycotoxin-related issues in aquaculture industry has grown as manufacturers and producers realise the importance of mycotoxins, beyond aflatoxin, and their potential to impact production. During a period of one year (January 2016 – December 2016), 175 samples of different plant proteins, aquaculture/fishery by-products and finished aquaculture feeds, were analysed. Samples were tested for aflatoxins (aflatoxin B1, B2, G1 and G2); zearalenone; type B trichothecenes (deoxynivalenol (DON); nivalenol; 3-acetyldeoxynivalenol; 15-acetyldeoxynivalenol and fusarenon X-glucoside); fumonisins (fumonisin B1, B2 and B3); type A trichothecenes (T-2 and HT-2 toxin; diacetoxyscirpenol and neosolaniol); and ochratoxin A. All samples were sourced in Southeast Asia. Within the analysed samples, 4% were free of detectable mycotoxins. 8% of the samples had one mycotoxin and 88% of the samples were contaminated with more than one mycotoxin. The current work show similarity to previous studies, that mycotoxin occurrence in plant-meals, and consequently in finished feeds, is quite variable and confirms that aflatoxin is not the main mycotoxin in aquafeeds. Mycotoxin occurrence in fish and shrimp feeds in the present samples were higher than reported in previous studies for the same region. In samples of shrimp feed with DON detected, the mean average DON level was 882 μg/kg with a maximum level of 2,287 μg/kg. These values are within the reported sensitivity levels of white leg shrimp (Litopenaeus vannamei). Despite the limited number and short period of sampling, this inventory study helps address a knowledge gap of mycotoxin occurrence in feeds specifically destined for the aquaculture industry.

Sustainable intensification of aquaculture value chains between Asia and Europe: A framework for understanding impacts and challenges

Sustainable intensification (SI) is defined and interpreted in terms of a framework to support production of farmed aquatic animals in Asia and their trade with Europe. A novel holistic perspective to value chain analysis, informed by a range of sustainability tools, is used to explain the dynamic in the trade that is having significant impacts on livelihoods in both regions. The origins of SI in agriculture are first described and their congruence with aquaculture clarified. Asian aquaculture systems, based on their emergent properties, are then located within a SI framework considering possible boundaries (enterprise, zone or whole value chain). The implications of conventional intensification, and alternatives are explored with reference to specific examples and impacts on the local and global environment, human and aquatic animal health and welfare. The challenges to sustainability of such value chains and implications for their governance, food culture and consumer habits are considered. Local consumption of seafood in Asia is found to be a major driver of growth and alternative markets for exports regionally and in Low and Medium income countries (LMIC) are likely to impact on employment and power in the value chain between Europe and Asia. The benefits of viewing farmed seafood as part of broader food landscapes are identified in the analysis, as is a shift in the focus from volume to value in terms of goal setting. More holistic perspectives of sustainability also emerge as necessary to describe and interpret global value chains rather than limited reductionist, production- orientated views. A diversity of trends in the development of farmed seafood is identified in contrast to any simplistic move to intensification, likely informed by economic, environmental and social factors in producer and consumer countries. Statement of relevanceGlobal imbalances in production and consumption of farmed seafood are stimulating trade between Asia and Europe. The dynamic of global value chains around this emergent trade and their alignment with broader sustainability criteria, as applied to sustainable intensification of food production, are highly relevant to global food security.

Molecular characterization, tissue distribution and differential nutritional regulation of putative Elovl5 elongase in silver barb (Puntius gonionotus)

Fatty acid desaturase (Fads) and elongase (Elovl) are two important enzymes involved in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs) in fishes. Silver barb (Puntius gonionotus) is considered a promising medium carp species for freshwater aquaculture in Asia. Earlier, Δ6 fads cDNA was characterized to understand the molecular mechanism of LC-PUFA biosynthesis in this species. In the present study elovl5-like elongase full-length cDNA was cloned and characterized by RACE (rapid amplification of cDNA ends), and analyzed its basal expression in various organs/tissues by quantitative real time PCR (qRT-PCR) assay. Differential expression of elovl5 cDNA in various tissues following replacement of fish oil (FO) with linseed oil (LO) in the diet also studied. The full length cDNA sequence of silver barb elovl5-like elongase consisted of 1853bp, including an open reading frame (ORF) of 876bp encoding a precursor protein of 291 amino acids possessing the entire characteristic features of Elovl protein. The elovl5 transcript was constitutively expressed in all the tissues examined: muscle, liver, brain, kidney, skin, intestine, gill and eye. The expression of elovl5 gene was upregulated, whereas the serum biochemical constituents were either remain unchanged or lowered following replacement of FO with LO in the diets. We report for the first time, an in silico 3D structure model of elongase protein from silver barb. All these findings may contribute to a better understanding the potential regulatory mechanisms involved and may be useful for enhancing endogenous LC-PUFA production in silver barb.

Differential gene expression and SNP association between fast- and slow-growing turbot (Scophthalmus maximus)

Growth is among the most important traits for animal breeding. Understanding the mechanisms underlying growth differences between individuals can contribute to improving growth rates through more efficient breeding schemes. Here, we report a transcriptomic study in muscle and brain of fast- and slow-growing turbot (Scophthalmus maximus), a relevant flatfish in European and Asian aquaculture. Gene expression and allelic association between the two groups were explored. Up-regulation of the anaerobic glycolytic pathway in the muscle of fast-growing fish was observed, indicating a higher metabolic rate of white muscle. Brain expression differences were smaller and not associated with major growth-related genes, but with regulation of feeding-related sensory pathways. Further, SNP variants showing frequency differences between fast- and slow-growing fish pointed to genomic regions likely involved in growth regulation, and three of them were individually validated through SNP typing. Although different mechanisms appear to explain growth differences among families, general mechanisms seem also to be involved, and thus, results provide a set of useful candidate genes and markers to be evaluated for more efficient growth breeding programs and to perform comparative genomic studies of growth in fish and vertebrates.