Draft genome sequences of 13 Tenacibaculum maritimum isolates from farmed Norwegian Cyclopterus lumpus (lumpfish) and Scophthalmus maximus (turbot)

Thirteen bacterial isolates of Tenacibaculum maritimum were sequenced and assembled. The strains were isolated from four disease outbreaks in farmed marine fish in Norway. Eight isolates were from Cyclopterus lumpus (lumpfish), and five were from Scophthalmus maximus (turbot). Overall, sequence similarity did not correlate with host species or geographic location.

Experimental Infection and the Effects of Temperature on the Pathogenicity of the Infectious Spleen and Kidney Necrosis Virus in Juvenile Nile Tilapia (Oreochromis niloticus)

The infectious spleen and kidney necrosis virus (ISKNV) is one of the most important emerging viral pathogens for Nile tilapia (Oreochromis niloticus) farming. While prevalent worldwide, it has recently been detected in Brazil. However, despite the importance of the virus and the affected fish species, there are no scientific data on the effects of water temperature on disease pathogenesis in Nile tilapia. In the present study, we conducted two trials using juvenile Nile tilapia over a 15-day period. In trial 1, an experimental infection model was developed based on the intraperitoneal inoculation of active viral homogenates (4.3 × 104 virus fish-1), while control fish were similarly inoculated with inactivated viral homogenates. In trial 2, the fish were maintained at different water temperatures (26, 28, 30, 32, and 34 °C) and then infected with ISKNV. For virus detection, kidney and spleen samples were collected and analyzed by qPCR. Our results show that the disease was successfully reproduced in experimental conditions with active homogenates, with the first signs of the disease appearing on the third day after infection. In addition, a significant reduction in mortality was observed in the groups maintained at higher temperatures (>30 °C). This suggests that a treatment of the disease with non-lethal hyperthermia can be used to control the symptoms and mortality of ISKNV-infected Nile tilapia juveniles.

Levamisole incorporation in fish feed - Ensuring the medication dose and avoidance of leaching into the water

Levamisole, an anthelmintic and immunostimulant drug, has been studied as a promising alternative for aquaculture use. While oral administration through feeding is the main route of administration in fish farming, no studies evaluating methods of levamisole incorporation into the feed have been reported so far. Therefore, this study aimed to evaluate potential procedures for levamisole incorporation in extruded fish feed using ethyl cellulose, gelatin, or vegetable oil, to avoid drug leaching to the water during the animal's medication. A suitable LC-MS/MS method was optimized (full factorial design), validated, and applied to evaluate the efficiency of the process, the homogeneity of the drug concentration, and the leaching rate. The method has been demonstrated to be selective, precise (RSD < 4.9%), accurate (recovery > 98.4%), and linear (r > 0.99, 125-750 mg kg-1). The incorporation procedures using the three coating agents showed high incorporation efficiency (70%) and a homogeneous drug concentration among the extruded feed pellets. A low levamisole leaching rate was verified in the feed prepared using the ethyl cellulose coating procedure (4.3% after 15 min of immersion in the water). On the other hand, fish feed coated with gelatin and oil resulted in a high leaching rate (30-35% after 15 min). Thus, this study shows that coating ethyl cellulose may be a promising procedure for levamisole incorporation in fish feed and with the potential to enhance its use in animal production while reducing environmental contamination.

Investigating the role of genetic variation in vgll3 and six6 in the domestication of gilthead seabream (Sparus aurata Linnaeus) and European seabass (Dicentrarchus labrax Linnaeus)

Gene function conservation is crucial in molecular ecology, especially for key traits like growth and maturation in teleost fish. The vgll3 and six6 genes are known to influence age-at-maturity in Atlantic salmon, but their impact on other fish species is poorly understood. Here, we investigated the association of vgll3 and six6 in the domestication of gilthead seabream and European seabass, both undergoing selective breeding for growth-related traits in the Mediterranean. We analysed two different sets of samples using two different genotyping approaches. The first dataset comprised farmed and wild populations from Greece, genotyped for SNPs within the two genes ('gene-level genotyping'). The second dataset examined 300-600 k SNPs located in the chromosomes of the two genes, derived from a meta-analysis of a Pool-Seq experiment involving farmed and wild populations distributed widely across the Mediterranean ('chromosome-level genotyping'). The gene-level analysis revealed a statistically significant allele frequency differences between farmed and wild populations on both genes in each species. This finding was partially supported by the chromosome-level analysis, identifying highly differentiated regions may be involved in the domestication process at varying distances from the candidate genes. Noteworthy genomic features were found, such as a CpG island in gilthead seabream and novel candidate genes in European seabass, warranting further investigation. These findings support a putative role of vgll3 and six6 in the maturation and growth of gilthead seabream and European seabass, emphasizing the need for further research on their conserved function.

Membrane aerated biofilm reactor in recirculating aquaculture system for effluent treatment

The implementation of fish farming has been increasing worldwide over the last decades, as well the search for alternative production systems and the treatment of their generated effluent. Recirculating Aquaculture System (RAS) is a compact solution for future intensive fish farming. However, few configurations of treatment technologies were tested in RAS, such as systems with a Membrane Aerated Biofilm Reactor (MABR). In this scene, this study aimed to evaluate the RAS effluent treatment efficiency device for intensive Nile tilapia (Oreochromis niloticus) production, the fish species most cultivated worldwide. The novel RAS configuration was composed of a cultivation tank (CT), a Column Settler, and a MABR. The RAS performance was evaluated by pH, temperature, turbidity, dissolved oxygen (DO), total nitrogen (TN), ammonia, nitrite, nitrate, total solids (TS), and chemical oxygen demand (COD). The obtained results in average values for temperature, pH, and DO inside the CT were 25.22 ± 1.88°C, 7.61 ± 0.33, and 3.80 ± 1.30 mg L-1, respectively, as ideal for tilapias survival. Average removal efficiencies found in the RAS for turbidity, COD, TN, nitrite, nitrate, ammonia, and TS were 50.0, 40.5, 11.7, 40.2, 13.1, 35.0, and 11.4%, respectively. Overall, we observed removals for all parameters studied, with good results, particularly, for COD, turbidity, nitrite, and ammonia. The evaluated system proved an effective alternative for water reuse in RAS capable of maintaining water quality characteristics within the recommended values for fish farming.

The Patterns of Migration of Potentially Toxic Elements from Coal Mining Subsidence Areas and Associated Soils to Waterlogged Areas

It is crucial for effectively controlling potentially toxic element (PTE) pollution to understand the pollution situation, ecological risks, health risks, and migration patterns of PTEs. However, currently, no research has been conducted on the migration patterns of soil PTEs from coal mining subsidence areas to waterlogged areas under different restoration modes. In this study, a total of 15 sediment samples and 60 soil samples were collected from landscaped wetlands, aquaculture wetland, fish-photovoltaic complementary wetland, photovoltaic wetland, and waterlogged areas with untreated coal mining subsidence. The PTE pollution status, ecological risks, health risks, migration patterns, and the important factors influencing the migration were analyzed. The results indicated that the comprehensive pollution level of PTEs in waterlogged areas with coal mining subsidence can be reduced by developing them into landscaped wetlands, aquaculture wetlands, fish-photovoltaic complementary wetlands, and photovoltaic wetlands. Additionally, the closer to the waterlogged area, the higher the Cu content in the subsidence area soil is, reaching its peak in the waterlogged area. The Cd was influenced positively by SOC and pH. The research results were of great significance for formulating reclamation plans for waterlogged areas and controlling PTE pollution.

Effects of stress conditions on plasma parameters and gene expression in the skin mucus of farmed rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the physiological response of rainbow trout (Oncorhynchus mykiss) before slaughtering in the last phase of farming analyzing skin mucus and plasma. Two groups of rainbow trout were considered: Group UN ("unstressed"), represented by fish randomly captured from raceways, in the last phase of a standard fattening cycle; Group S ("stressed"), collected at the end of the pre-slaughtering tank, soon after slaughtering. The fish skin mucus was swabbed from head to tail using a sterile plastic spatula and the blood was collected through an endocardial puncture. qRT-PCR was used to study the gene expression in skin mucus. The mRNA expression levels of the IL-6 and IgD genes were higher in the S than in the Group UN. The plasma analysis showed an only a decrease in the glucose plasma levels in the Group S when compared to the Group UN. The present results indicated that the procedures adopted after slaughtering only affected changes in plasma glucose and skin mucus activity in rainbow trout suggesting that management protocol was compatible with non-stressful farming conditions.

Occupational Health and Safety in Tanzanian Aquaculture - Emerging Issues

OBJECTIVES

The Tanzanian aquaculture industry represents great potential for food production and jobs; however, the potential occupational hazards and health risks associated with the sector have not been assessed. The aim of this study was to conduct a scoping analysis of the status of occupational health and safety based on current Tanzanian aquaculture activities, specifically in the fish farming and seaweed farming sectors.

METHODS

Relevant information for the scoping analysis was obtained through aquaculture site visits and worker observation, interviews with key aquaculture stakeholders, and a review of literature relevant to the Tanzanian aquaculture sector published in scientific communications as well as grey literature.

RESULTS

The study shows that the Tanzanian aquaculture industry is still in nascent stages, especially in relation to occupational health and safety despite some well-established isolated operations in the country. The industry is dominated by small-scale fish and seaweed farmers, the majority of whom work in the informal and semi-formal sectors. Tanzanian aquaculture workers are exposed to a number of occupational hazards and their associated health effects have been poorly characterized. Substantial gender disparities exist within the sector, which together with climate change, impact worker health and safety.

CONCLUSION

Future research should focus on characterizing occupational exposures and documenting the associated health effects in Tanzanian aquaculture workers. Standardized methods should be used for this purpose to take into account gender disparities as well as the impact of climate change on occupational health and safety of these vulnerable workers.

Impacts of the Residual Trace Metals of Aquaculture in Net Cages on the Quality of Sediment

Anthropogenic pollution by trace metals in aquatic environments in semiarid zones is a critical area of investigation. The objective of this study was to investigate the concentration and spatial distribution of trace metals in surface sediments in the Rosário reservoir, which is affected by the intensive aquaculture of Tilápia-do-Nilo (Oreochromis niloticus). Sediment samples were collected in three different areas, postculture (PCTV), cultivation (CTV) and control (CTRL) in the dry season in 2019. The granulometric composition, organic matter and concentrations of Fe, Mn, Zn, Cu, Cr, Cd, Pb and Ni metals were determined. Multivariate statistics were used. Geochemical and ecotoxicological indices and a comparison with sediment quality guidelines (SQG) were used. The sediment was characterized by silty clay loam with an average organic matter of 18.76 ± 4.27. The analytical merit figures demonstrated accuracy (metal recoveries in certified standards) between 89 to 99% and high precision (RSD < 5%). The concentration ranges for the metals were Fe: 0.11-0.85 (%), Mn: 14.46-86.91, Zn: 2.6-220.56, Cu: 26.89-98.75, Cr: 60.18-76.06, Cd: 0.38-0.59, Pb: 18.13-43.13, and Ni: 34.4-46.75, all in (mg/kg^-1). The highest concentration values were found in the CTV areas (Fe: 40 ± 0.22, Mn: 66.48 ± 19.11, Zn: 114.83 ± 59.75 and Cr: 70.85 ± 2.62) and PCTV (Cd: 0.53 ± 0.04, Cu: 71.83 ± 21.20, Pb: 33.71 ± 4.34 and Ni: 44.60 ± 1.79). Pearson's correlation, hierarchical cluster analysis and principal component analysis confirmed the influence of fish farming on metals. Only Ni presented concentration values higher than the reference value established in the SQG. Thus, considering the probable geochemical and ecotoxicological effects, they comprise the two lowest levels of impact.

Phytase Supplementation under Commercially Intensive Rearing Conditions: Impacts on Nile Tilapia Growth Performance and Nutrient Digestibility

This study evaluated the effects of phytase supplementation on growth performance and apparent digestibility of Nile tilapia (Oreochromis niloticus) in a commercial fish farm setting. Nile tilapia (6300 male, 57.48 ± 1.04 g) were randomly stocked into 42 floating cages. The experimental design was completely randomized, comprising six treatments and seven replications. Fish were fed five phosphorus deficient plant-based diets with graded levels of phytase supplementation (0, 500, 1000, 1500, 2000 UF kg^-1) and an additional diet containing phosphorus supplementation to meet the requirement of this fish species (positive control). After 97 days of feeding, growth performance data were collected and 900 fish (500 ± 10 g) were relocated to 6 floating cages for the digestibility assessment. Quadratic polynomial regression analysis indicated 1537.5 and 1593.2 UF kg^-1 as the optimum dietary levels for daily weight gain and feed conversion rate, respectively. Including 2000 UF kg^-1 resulted in the higher dry matter, crude protein, energy, and ash apparent digestibility coefficient values. Therefore, phytase supplementation from 1500 to 2000 UF kg^-1 is recommended to enhance growth performance and nutrient bioavailability of Nile tilapia reared according to industry practices.

Salmonella spp. in Aquaculture: An Exploratory Analysis (Integrative Review) of Microbiological Diagnoses between 2000 and 2020

The present study aimed to characterize, through descriptive statistics, data from scientific articles selected in a systematic integrative review that performed a microbiological diagnosis of Salmonella spp. in aquaculture. Data were obtained from research articles published in the BVS, Scielo, Science Direct, Scopus and Web of Science databases. The selected studies were published between 2000 and 2020 on samples of aquaculture animal production (fish, shrimp, bivalve mollusks, and other crustaceans) and environmental samples of aquaculture activity (farming water, soil, and sediments). After applying the exclusion criteria, 80 articles were selected. Data such as country of origin, categories of fish investigated, methods of microbiological diagnosis of Salmonella spp., sample units analyzed and most reported serovars were mined. A textual analysis of the word cloud and by similarity and descending hierarchical classification with the application of Reinert's algorithm was performed using R® and Iramuteq® software. The results showed that a higher percentage of the selected articles came from Asian countries (38.75%). Fish was the most sampled category, and the units of analysis of the culture water, muscle and intestine were more positive. The culture isolation method is the most widespread, supported by more accurate techniques such as PCR. The most prevalent Salmonella serovars reported were S. Typhimurium, S. Weltevreden and S. Newport. The textual analysis showed a strong association of the terms "Salmonella", "fish" and "water", and the highest hierarchical class grouped 25.4% of the associated text segments, such as "aquaculture", "food" and "public health". The information produced characterizes the occurrence of Salmonella spp. in the aquaculture sector, providing an overview of recent years. Future research focusing on strategies for the control and prevention of Salmonella spp. in fish production are necessary and should be encouraged.

Ovicidal effect of essential oils of Lippia alba, Lippia sidoides and Lippia gracilis on the acanthocephalan Neoechinorhynchus buttnerae (Eoacanthocephala: Neoechinorhynchidae)

Acanthocephalosis in tambaqui Colossoma macropomum culture is a limiting factor for the production of the species, being the most recurrent, which makes it necessary to develop strategies to control parasitosis even in the early stages of parasite development. This study aimed to elucidate the morphological characteristics of eggs of the acanthocephalan Neoechinorhynchus buttnerae and the ovicidal effect of the essential oils of Lippia alba, Lippia sidoides, and Lippia gracilis. The parasites were collected from hosts naturally infected with N. buttnerae, and the eggs obtained from the female 'parasites' abdominal cavity were added to 12-well plates containing the essential oils at different dilutions. After the eggs (N = 300) were separated and measured (length and width) with the aid of an optical microscope coupled to a digital program, the viability of the treated eggs was monitored 24 h after treatments, L. gracilis essential oil was 100% effective at the highest concentration, whereas L. sidoides essential oil showed over 50% efficacy at 2 mg/ml, reaching 100% efficacy at all higher concentrations. Lippia. alba essential oil did not show satisfactory efficacy in preventing N. buttnerae egg hatching.

Projecting global mariculture production and adaptation pathways under climate change

The sustainability of global seafood supply to meet increasing demand is facing several challenges, including increasing consumption levels due to a growing human population, fisheries resources over-exploitation and climate change. Whilst growth in seafood production from capture fisheries is limited, global mariculture production is expanding. However, climate change poses risks to the potential seafood production from mariculture. Here, we apply a global mariculture production model that accounts for changing ocean conditions, suitable marine area for farming, fishmeal and fish oil production, farmed species dietary demand, farmed fish price and global seafood demand to project mariculture production under two climate and socio-economic scenarios. We include 85 farmed marine fish and mollusc species, representing about 70% of all mariculture production in 2015. Results show positive global mariculture production changes by the mid and end of the 21^st century relative to the 2000s under the SSP1-2.6 scenario with an increase of 17%±5 and 33%±6, respectively. However, under the SSP5-8.5 scenario, an increase of 8%±5 is projected, with production peaking by mid-century and declining by 16%±5 towards the end of the 21^st century. More than 25% of mariculture-producing nations are projected to lose 40%-90% of their current mariculture production potential under SSP5-8.5 by mid-century. Projected impacts are mainly due to the direct ocean warming effects on farmed species and suitable marine areas, and the indirect impacts of changing availability of forage fishes supplies to produce aquafeed. Fishmeal replacement with alternative protein can lower climate impacts on a subset of finfish production. However, such adaptation measures do not apply to regions dominated by non-feed-based farming (i.e. molluscs) and regions losing substantial marine areas suitable for mariculture. Our study highlights the importance of strong mitigation efforts and the need for different climate adaptation options tailored to the diversity of mariculture systems, to support climate-resilient mariculture development.

Parasitism of Arapaima gigas (Schinz, 1822) in fish farms of the state of Amazonas, Brazil

The objective of this study was to investigate the parasites occurrences and to determine the rates of infestation/parasitic infection in juvenile Arapaima gigas from seven fish farms in the state of Amazonas, relating to the characteristics of these fish farms. Of the 70 A. gigas evaluated, 43 were infested/infected, with a total of 133 parasites collected. Three fish farms (2, 4, 6) showed the highest levels of prevalence of parasites (100%, 70%, 70%), mean intensity (4.1±2.6, 8.1±9.2, and 2.1±1.3), and mean abundance (4.1±2.6, 5.7±8.1, and 1.5±1.5), respectively. Prevalence ranged from 30% to 100%, mean intensity from 1.0 to 8.1 and mean abundance from 0.3 to 5.7. Monogenea, Digenea, Nematoda (Hysterothylacium sp. and Spirocamallanus sp.) and Acanthocephala (Neoechinorhynchus sp. and Polyacanthorhynchus sp.) were identified. The parasites Hysterothylacium sp. and Neoechinorhynchus sp. were the most prevalent parasites with 31.43% and 15.71%, respectively. The fish presented negative allometry in growth and constant condition factor. Measures to prevent and control the parasitic diseases diagnosed are discussed as well prophylactic practices that contribute to the biosecurity of the farms.

Linking Pedigree Information to the Gene Expression Phenotype to Understand Differential Family Survival Mechanisms in Highly Fecund Fish: A Case Study in the Larviculture of Pacific Bluefin Tuna

Mass spawning in fish culture often brings about a marked variance in family size, which can cause a reduction in effective population sizes in seed production for stock enhancement. This study reports an example of combined pedigree information and gene expression phenotypes to understand differential family survival mechanisms in early stages of Pacific bluefin tuna, Thunnus orientalis, in a mass culture tank. Initially, parentage was determined using the partial mitochondrial DNA control region sequence and 11 microsatellite loci at 1, 10, 15, and 40 days post-hatch (DPH). A dramatic proportional change in the families was observed at around 15 DPH; therefore, transcriptome analysis was conducted for the 15 DPH larvae using a previously developed oligonucleotide microarray. This analysis successfully addressed the family-specific gene expression phenotypes with 5739 differentially expressed genes and highlighted the importance of expression levels of gastric-function-related genes at the developmental stage for subsequent survival. This strategy demonstrated herein can be broadly applicable to species of interest in aquaculture to comprehend the molecular mechanism of parental effects on offspring survival, which will contribute to the optimization of breeding technologies.

A Taxonomy of Food Supply Chain Problems from a Computational Intelligence Perspective

In the last few years, the Internet of Things, and other enabling technologies, have been progressively used for digitizing Food Supply Chains (FSC). These and other digitalization-enabling technologies are generating a massive amount of data with enormous potential to manage supply chains more efficiently and sustainably. Nevertheless, the intricate patterns and complexity embedded in large volumes of data present a challenge for systematic human expert analysis. In such a data-driven context, Computational Intelligence (CI) has achieved significant momentum to analyze, mine, and extract the underlying data information, or solve complex optimization problems, striking a balance between productive efficiency and sustainability of food supply systems. Although some recent studies have sorted the CI literature in this field, they are mainly oriented towards a single family of CI methods (a group of methods that share common characteristics) and review their application in specific FSC stages. As such, there is a gap in identifying and classifying FSC problems from a broader perspective, encompassing the various families of CI methods that can be applied in different stages (from production to retailing) and identifying the problems that arise in these stages from a CI perspective. This paper presents a new and comprehensive taxonomy of FSC problems (associated with agriculture, fish farming, and livestock) from a CI approach; that is, it defines FSC problems (from production to retail) and categorizes them based on how they can be modeled from a CI point of view. Furthermore, we review the CI approaches that are more commonly used in each stage of the FSC and in their corresponding categories of problems. We also introduce a set of guidelines to help FSC researchers and practitioners to decide on suitable families of methods when addressing any particular problems they might encounter. Finally, based on the proposed taxonomy, we identify and discuss challenges and research opportunities that the community should explore to enhance the contributions that CI can bring to the digitization of the FSC.

The Impact of Intensive Fish Farming on Pond Sediment Microbiome and Antibiotic Resistance Gene Composition

Aquaculture is a fast-growing animal food sector, and freshwater fish farming is particularly common in Central and Eastern Europe. As the biodiversity of fishery ponds is changed toward fulfilling the industrial needs, precautions should be taken to keep the system sustainable and protect the adjacent environment from possible damage. Due to risk of infectious diseases, antibiotics are used in aquaculture production systems. The constant exposure to antimicrobials can contribute to the rise of antibiotic resistance in aquaculture products and the adjacent ecosystems, with possibility of dissemination to the wider environment as well as between animals and humans. Even though previous studies have found antibiotic resistance genes in the sediments and water of farming ponds, the tendency and direction of spreading is not clear yet. The objective of this project was to evaluate the influence of intensive fish farming on the condition of water bodies used for the aquaculture and the environment, concentrating on the impact of the aquaculture on the surrounding water ecosystems as well as the possibility of transferring the pollutants and antibiotic resistance genes to both environment and the human hosts. Combined measurement of antibiotic and heavy metal contamination, toxicity assessment, microorganism diversity, and the detection of common antibiotic resistance genes was performed in the sediments of one fishery farm ponds as well as sampling points upstream and downstream. All the tested sediment samples did not show significantly elevated heavy metal concentrations and no substantial veterinary antibiotic pollution. From the antibiotic resistance genes tested, the presence of aminoglycoside and β-lactam resistance determinants as well as the presence of integrons could be of concern for the possibility of transfer to humans. However, despite the lack of heavy metal and antibiotic pollution, the sediments showed toxicity, the cause of which should be explored more.

The use of probiotics in animal feeding for safe production and as potential alternatives to antibiotics

Although the production of safe food for human consumption is the primary purpose for animal rearing, the environment and well-being of the animals must also be taken into consideration. Based on microbiological point of view, the production of healthy food from animals involves considering foodborne pathogens, on the one hand and on the other hand, the methods used to fight against germs during breeding. The conventional method to control or prevent bacterial infections in farming is the use antibiotics. However, the banning of these compounds as growth promoters caused many changes in animal breeding and their use has since been limited to the treatment and prevention of bacterial infections. In this function, their importance no longer needs to be demonstrated, but unfortunately, their excessive and abusive use have led to a double problem which can have harmful consequences on consumer health: Resistance to antibiotics and the presence of antibiotic residues in food. The use of probiotics appears to be a suitable alternative to overcome these problems because of their ability to modulate the immune system and intestinal microflora, and further considering their antagonistic role against certain pathogenic bacteria and their ability to play the role of growth factor (sometimes associated with prebiotics) when used as feed additives. This review aims to highlight some of the negative effects of the use of antibiotics in animal rearing as well as emphasize the current knowledge on the use of probiotics as a feed additive, their influence on animal production and their potential utility as an alternative to conventional antibiotics, particularly in poultry, pig, and fish farming.

Raising awareness of antimicrobial resistance in rural aquaculture practice in Bangladesh through digital communications: a pilot study

One of the key strategic objectives of the World Health Organisation’s global antimicrobial resistance (AMR) action plan is to improve public awareness and understanding of this issue. Very few AMR awareness campaigns have targeted the animal production sector, particularly in low- and middle-income countries (LMICs) where rural communities can be geographically difficult to access via traditional face-to-face community engagement methods. Aquaculture is a major food production industry in Bangladesh and across Asia, an area which poses a significant risk to global AMR dissemination. In this pilot study, we sought to investigate the potential for digital communication materials to rapidly and effectively communicate AMR messages to rural aquaculture farmers in Bangladesh. Working with stakeholders from the Bangladesh aquaculture industry, we developed a 4-minute digital animation designed specifically for this audience and assessed its capacity to engage and communicate AMR messages to farmers. We then conducted a small-scale social media campaign, to determine the potential for rapidly disseminating AMR awareness materials to a large audience across Bangladesh, where there is an extensive 4 G internet network and an ever-increasing proportion of the population (57% as of December 2019) have mobile internet access. Thirty-six farmers were surveyed: all of them liked this method of communication and 97% said it would change the way they use antibiotics in the future. Through the social media campaign, the animation received 9,100 views in the first 2 weeks alone. Although preliminary, these results demonstrate the huge potential for digital communication methods for the rapid and widespread communication of AMR awareness materials to rural aquaculture communities in Bangladesh and across Asia. Our results support the need for more research into the most appropriate and effective content of AMR awareness campaigns for aquaculture communities and question the need for explaining the science underlying AMR in such communication materials.

Sterilization of sea lice eggs with ultraviolet C light: towards a new preventative technique for aquaculture

BACKGROUND

Sea lice infestations on Atlantic salmon (Salmo salar) farms are a considerable burden on the industry and put wild salmonid populations at risk. Frequent delousing treatments are necessary to keep lice densities below allowable limits, but currently viable treatments have drawbacks in terms of financial cost, animal welfare, or environmental impacts. We tested if 254 nm ultraviolet C light (UVC) could function as a new preventative method to suppress reproduction of salmon lice (Lepeophtheirus salmonis) by sterilizing fertilized eggs. We exposed salmon lice eggstrings to a range of UVC intensities and durations to identify effective doses.

RESULTS

A cumulative dose of 0.008 J cm^-2 induced 5% egg mortality, while 95% egg mortality occurred at 0.09 J cm^-2 , indicating that UVC can be effective as a preventative treatment. The total cumulative dose appeared to be more important than the duration or number of individual exposures by which the total dose was achieved.

CONCLUSION

UVC treatment has immediate applications for the salmon aquaculture industry, including for the treatment of wastewater from delousing or other operations. Future work will assess the feasibility of UVC dose delivery on host salmon in sea cage environments that involves little or no fish handling and creates negligible environmental impacts. © 2019 Society of Chemical Industry.

Parasitic infection of Cobitis elongatoides Băcescu & Mayer, 1969 by zoonotic metacercariae Clinostomum complanatum (Rudolphi, 1814)

An infection of zoonotic Clinostomum complanatum metacercariae with potential human transmission was recorded close to fish farms in the Tisa River Basin of Slovakia and Ukraine. The prevalence varied from 19.4% to 81.3%, and the intensity of infection varied from 7 to 41. The results of a generalized linear model predicted a positive trend for the Cobitis elongatoides host and a standard length and intensity of infection, with females having a higher number of parasites. However, no significant impact was found of the intensity of infection on Clark's condition of the host. The metacercariae were primarily located in the anterior part of the host's body. Our study also showed significant evidence that water velocity affects the number of C. complanatum metacercariae, regardless of the host's (Cobitis) microhabitat.

Estimating the relative fitness of escaped farmed salmon offspring in the wild and modelling the consequences of invasion for wild populations

Throughout their native range, wild Atlantic salmon populations are threatened by hybridization and introgression with escapees from net-pen salmon aquaculture. Although domestic-wild hybrid offspring have shown reduced fitness in laboratory and field experiments, consequential impacts on population abundance and genetic integrity remain difficult to predict in the field, in part because the strength of selection against domestic offspring is often unknown and context-dependent. Here, we follow a single large escape event of farmed Atlantic salmon in southern Newfoundland and monitor changes in the in-river proportions of hybrids and feral individuals over time using genetically based hybrid identification. Over a three-year period following the escape, the overall proportion of wild parr increased consistently (total wild proportion of 71.6%, 75.1% and 87.5% each year, respectively), with subsequent declines in feral (genetically pure farmed individuals originating from escaped, farmed adults) and hybrid parr. We quantify the strength of selection against parr of aquaculture ancestry and explore the genetic and demographic consequences for populations in the region. Within-cohort changes in the relative proportions of feral and F1 parr suggest reduced relative survival compared to wild individuals over the first (0.15 and 0.81 for feral and F1, respectively) and second years of life (0.26, 0.83). These relative survivorship estimates were used to inform an individual-based salmon eco-genetic model to project changes in adult abundance and overall allele frequency across three invasion scenarios ranging from short-term to long-term invasion and three relative survival scenarios. Modelling results indicate that total population abundance and time to recovery were greatly affected by relative survivorship and predict significant declines in wild population abundance under continued large escape events and calculated survivorship. Overall, this work demonstrates the importance of estimating the strength of selection against domestic offspring in the wild to predict the long-term impact of farmed salmon escape events on wild populations.

Density-dependent changes in neophobia and stress-coping styles in the world's oldest farmed fish

Farmed fish are typically reared at densities much higher than those observed in the wild, but to what extent crowding results in abnormal behaviours that can impact welfare and stress coping styles is subject to debate. Neophobia (i.e. fear of the 'new') is thought to be adaptive under natural conditions by limiting risks, but it is potentially maladapted in captivity, where there are no predators or novel foods. We reared juvenile Nile tilapia (Oreochromis niloticus) for six weeks at either high (50 g l-1) or low density (14 g l-1), assessed the extent of skin and eye darkening (two proxies of chronic stress), and exposed them to a novel object in an open test arena, with and without cover, to assess the effects of density on neophobia and stress coping styles. Fish reared at high density were darker, more neophobic, less aggressive, less mobile and less likely to take risks than those reared at low density, and these effects were exacerbated when no cover was available. Thus, the reactive coping style shown by fish at high density was very different from the proactive coping style shown by fish at low density. Our findings provide novel insights into the plasticity of fish behaviour and the effects of aquaculture intensification on one of the world's oldest farmed and most invasive fish, and highlight the importance of considering context. Crowding could have a positive effect on the welfare of tilapia by reducing aggressive behaviour, but it can also make fish chronically stressed and more fearful, which could make them less invasive.

Current status of parasitic ciliates Chilodonella spp. (Phyllopharyngea: Chilodonellidae) in freshwater fish aquaculture

Freshwater fish farming contributes to more than two-thirds of global aquaculture production. Parasitic ciliates are one of the largest causes of production loss in freshwater farmed fishes, with species from the genus Chilodonella being particularly problematic. While Chilodonella spp. include 'free-living' fauna, some species are involved in mortality events of fish, particularly in high-density aquaculture. Indeed, chilodonellosis causes major productivity losses in over 16 species of farmed freshwater fishes in more than 14 countries. Traditionally, Chilodonella species are identified based on morphological features; however, the genus comprises yet uncharacterized cryptic species, which indicates the necessity for molecular diagnostic methods. This review synthesizes current knowledge on the biology, ecology and geographic distribution of harmful Chilodonella spp. and examines pathological signs, diagnostic methods and treatments. Recent advances in molecular diagnostics and the ability to culture Chilodonella spp. in vitro will enable the development of preventative management practices and sustained freshwater fish aquaculture production.

Intensive aquaculture selects for increased virulence and interference competition in bacteria

Although increased disease severity driven by intensive farming practices is problematic in food production, the role of evolutionary change in disease is not well understood in these environments. Experiments on parasite evolution are traditionally conducted using laboratory models, often unrelated to economically important systems. We compared how the virulence, growth and competitive ability of a globally important fish pathogen, Flavobacterium columnare, change under intensive aquaculture. We characterized bacterial isolates from disease outbreaks at fish farms during 2003-2010, and compared F. columnare populations in inlet water and outlet water of a fish farm during the 2010 outbreak. Our data suggest that the farming environment may select for bacterial strains that have high virulence at both long and short time scales, and it seems that these strains have also evolved increased ability for interference competition. Our results are consistent with the suggestion that selection pressures at fish farms can cause rapid changes in pathogen populations, which are likely to have long-lasting evolutionary effects on pathogen virulence. A better understanding of these evolutionary effects will be vital in prevention and control of disease outbreaks to secure food production.

Economic values of growth and feed efficiency for fish farming in recirculating aquaculture system with density and nitrogen output limitations: a case study with African catfish (Clarias gariepinus)

In fish farming, economic values (EV) of breeding goal traits are lacking, even though they are key parameters when defining selection objectives. The aim of this study was to develop a bioeconomic model to estimate EV of 2 traits representing production performances in fish farming: the thermal growth coefficient (TGC) and the feed conversion ratio (FCR). This approach was applied to a farm producing African catfish (Clarias gariepinus) in a recirculating aquaculture system (RAS). In the RAS, 2 factors could limit production level: the nitrogen treatment capacity of the biofilter or the fish density in rearing tanks at harvest. Profit calculation includes revenue from fish sales, cost of juveniles, cost of feed, cost of waste water treatment, and fixed costs. In the reference scenario, profit was modeled to zero. EV were calculated as the difference in profit per kilogram of fish between the current population mean for both traits (µt) and the next generation of selective breeding (µt+Δt) for either TGC or FCR. EV of TGC and FCR were calculated for three generations of hypothetical selection on either TGC or FCR (respectively 6.8% and 7.6% improvement per generation). The results show that changes in TGC and FCR can affect both the number of fish that can be stocked (number of batches per year and number of fish per batch) and the factor limiting production. The EV of TGC and FCR vary and depend on the limiting factors. When dissolved NH3-N is the limiting factor for both µt and µt+Δt, increasing TGC decreases the number of fish that can be stocked but increases the number of batches that can be grown. As a result, profit remains constant and EVTGC is zero. Increasing FCR, however, increases the number of fish stocked and the ratio of fish produced per kilogram of feed consumed ("economic efficiency"). The EVFCR is 0.14 €/kg of fish, and profit per kilogram of fish increases by about 10%. When density is the limiting factor for both µt and µt+Δt, the number of fish stocked per batch is fixed; therefore, extra profit is obtained by increasing either TGC, which increases the annual number of batches, or by decreasing FCR, which decreases annual feed consumption. EVTGC is 0.03 €/kg of fish and EVFCR is 0.05-0.06 €/kg of fish. These results emphasize the importance of calculating economic values in the right context to develop efficient future breeding programs in aquaculture.

Lamella dissolved air flotation treatment of fish farming effluents as a part of an integrated farming and effluent treatment concept

Nutrient emissions from fish farming can be reduced by a bag pen, i.e., a floating circular basin which serves simultaneously both as a fish cultivation tank and a swirl separation tank. Solid matter (excreta and uneaten feed) is collected at the bottom of the bag pen and pumped as an underflow to a dissolved air flotation (DAF) unit for nutrient removal. DAF equipped with lamella elements was studied in real conditions. Altogether 3000 rainbow trout females (2.0 kg each) were cultivated. Solid-water mixture was pumped from the bottom of the bag pen to an equalizing basin using a sequence of 2-min pumping followed by a 4-min pause. In some tests the influent was pumped directly and continuously from the bag pen to DAF. The influent quality changed substantially: average suspended solids (SS) and phosphorus (P) concentrations were 290 mg l⁻¹ ± 110 mg l⁻¹ and 3.2 mg l⁻¹ ± 1.2 mg l⁻¹, respectively. When the influent was fresh and P strongly associated with SS, DAF without precipitation chemicals produced up to 86% SS and 83% P removals. The influence of chemical doses was studied using 6.4-29.2 mg Fe l⁻¹ with hydraulic loadings (HLs) of 11.0-11.7 m h⁻¹. SS and P removal did not change substantially and the effluent concentration levelled at 30 mg SS l⁻¹ and 0.20-0.30 mg P l⁻¹, respectively. The lamella DAF, coupled with ferric precipitation, produced up to 90% P and 80% nitrogen reductions. HLs, excluding recycle water flow and lamella projection, up to 21 m h⁻¹ could be used.

Appearance traits in fish farming: progress from classical genetics to genomics, providing insight into current and potential genetic improvement

Appearance traits in fish, those external body characteristics that influence consumer acceptance at point of sale, have come to the forefront of commercial fish farming, as culture profitability is closely linked to management of these traits. Appearance traits comprise mainly body shape and skin pigmentation. Analysis of the genetic basis of these traits in different fish reveals significant genetic variation within populations, indicating potential for their genetic improvement. Work into ascertaining the minor or major genes underlying appearance traits for commercial fish is emerging, with substantial progress in model fish in terms of identifying genes that control body shape and skin colors. In this review, we describe research progress to date, especially with regard to commercial fish, and discuss genomic findings in model fish in order to better address the genetic basis of the traits. Given that appearance traits are important in commercial fish, the genomic information related to this issue promises to accelerate the selection process in coming years.

Meeting the food and nutrition needs of the poor: the role of fish and the opportunities and challenges emerging from the rise of aquaculture

People who are food and nutrition insecure largely reside in Asia and Sub-Saharan Africa and for many, fish represents a rich source of protein, micronutrients and essential fatty acids. The contribution of fish to household food and nutrition security depends upon availability, access and cultural and personal preferences. Access is largely determined by location, seasonality and price but at the individual level it also depends upon a person's physiological and health status and how fish is prepared, cooked and shared among household members. The sustained and rapid expansion of aquaculture over the past 30 years has resulted in >40% of all fish now consumed being derived from farming. While aquaculture produce increasingly features in the diets of many Asians, it is much less apparent among those living in Sub-Saharan Africa. Here, per capita fish consumption has grown little and despite the apparently strong markets and adequate biophysical conditions, aquaculture has yet to develop. The contribution of aquaculture to food and nutrition security is not only just an issue of where aquaculture occurs but also of what is being produced and how and whether the produce is as accessible as that from capture fisheries. The range of fish species produced by an increasingly globalized aquaculture industry differs from that derived from capture fisheries. Farmed fishes are also different in terms of their nutrient content, a result of the species being grown and of rearing methods. Farmed fish price affects access by poor consumers while the size at which fish is harvested influences both access and use. This paper explores these issues with particular reference to Asia and Africa and the technical and policy innovations needed to ensure that fish farming is able to fulfil its potential to meet the global population's food and nutrition needs.

Accuracy of the use of energy conversion factors for compound fish diets

Conversion factors of 23.6, 39.5 and 17.2 MJ/kg for protein, lipid and carbohydrate contents, respectively, are frequently used in fish studies to calculate the gross energy (GE) content of compound diets. Values predicted according to the above resulted in linear relationships of observed GE values with similar R (2) and mean prediction error (MPE) values when using either nitrogen-free extract (NFE) (R (2) = 0.5713, RMSE = 1.3134, MPE = 0.0741, n = 129, 32 studies) or starch (R (2) = 0.5665, RMSE = 1.6768, MPE = 0.0839, n = 190, 45 studies) as measurements of carbohydrate content. Apparent digestible carbohydrate content (either NFE or starch) was found to be linearly-related (R (2) values of 0.7531 and 0.7460, respectively) to its dietary content in compound fish diets. Predicted apparent digestible protein (ADP), lipid (DL) and carbohydrate contents, together with energy conversion factors, presented R (2) and MPE values of 0.6205 (RMSE = 1.2606) and 0.2051, respectively, between observed and predicted apparent digestible energy (ADE) content with NFE as measurement of carbohydrate content (n = 97, 17 studies, eight fish species). However, with carbohydrates quantified by starch content, an R (2) value of 0.7017 (RMSE = 1.7556) and MPE of 0.1055 were obtained (n = 37, 10 studies, five fish species).

Phage therapy and photodynamic therapy: low environmental impact approaches to inactivate microorganisms in fish farming plants

Owing to the increasing importance of aquaculture to compensate for the progressive worldwide reduction of natural fish and to the fact that several fish farming plants often suffer from heavy financial losses due to the development of infections caused by microbial pathogens, including multidrug resistant bacteria, more environmentally-friendly strategies to control fish infections are urgently needed to make the aquaculture industry more sustainable. The aim of this review is to briefly present the typical fish farming diseases and their threats and discuss the present state of chemotherapy to inactivate microorganisms in fish farming plants as well as to examine the new environmentally friendly approaches to control fish infection namely phage therapy and photodynamic antimicrobial therapy.

Utilization of dichlorvos and trichlorfon in salmonid farming in Norway during 1981-1988

The main objectives of this investigation were to quantify the use of dichlorvos and trichlorfon in the treatment of salmon lice infestations, to evaluate the prescribing of these drugs, and to estimate possible changes in the salmon lice problem by use of drug statistics. This study has shown that the use of trichlorfon increased from 4.9 tons in 1981 to 28.3 tons in 1985. This figure declined to 3.2 tons in 1988. The use of dichlorvos increased from 0.3 tons in 1986 to 3.2 tons in 1988. The change in the prescribing from trichlorfon to dichlorvos has dramatically reduced the pollution caused by these substances in the marine environment. Moreover, if necessary safety rules are observed, this change reduces the exposure of the workers on fish farms to these drugs, and also reduces the possibilities of intoxications of the fish during the treatment procedure. The sales figures of dichlorvos and trichlorfon, related to the calculated biomass of farmed salmonids in the sea, indicate a dramatic increase in the salmon lice problem.