Aquaculture Environment Research Articles

Assessing the Bacterial Community Composition of Bivalve Mollusks Collected in Aquaculture Farms and Respective Susceptibility to Antibiotics.

Aquaculture is a growing sector, providing several products for human consumption, and it is therefore important to guarantee its quality and safety. This study aimed to contribute to the knowledge of bacterial composition of Crassostrea gigas, Mytilus spp. and Ruditapes decussatus, and the antibiotic resistances/resistance genes present in aquaculture environments. Two hundred and twenty-two bacterial strains were recovered from all bivalve mollusks samples belonging to the Aeromonadaceae, Bacillaceae, Comamonadaceae, Enterobacteriaceae, Enterococcaceae, Micrococcaceae, Moraxellaceae, Morganellaceae, Pseudomonadaceae, Shewanellaceae, Staphylococcaceae, Streptococcaceae, Vibrionaceae, and Yersiniaceae families. Decreased susceptibility to oxytetracycline prevails in all bivalve species, aquaculture farms and seasons. Decreased susceptibilities to amoxicillin, amoxicillin/clavulanic acid, cefotaxime, cefoxitin, ceftazidime, chloramphenicol, florfenicol, colistin, ciprofloxacin, flumequine, nalidixic acid and trimethoprim/sulfamethoxazole were also found. This study detected six qnrA genes among Shewanella algae, ten qnrB genes among Citrobacter spp. and Escherichia coli, three oqxAB genes from Raoultella ornithinolytica and blaTEM-1 in eight E. coli strains harboring a qnrB19 gene. Our results suggest that the bacteria and antibiotic resistances/resistance genes present in bivalve mollusks depend on several factors, such as host species and respective life stage, bacterial family, farm’s location and season, and that is important to study each aquaculture farm individually to implement the most suitable measures to prevent outbreaks.

Automatic Monitoring of Relevant Behaviors for Crustacean Production in Aquaculture: A Review.

Simple SummaryAutomatic behavior monitoring, also called automated analytics or automated reporting, is the ability of an analytics platform to auto-detect relevant insights—anomalies, trends, patterns—and deliver them to users in real time, without users having to manually explore their data to find the answers they need. An analytics platform with automated behavior monitoring uses algorithms to auto-analyze datasets to search for notable changes in data. It then generates alerts at fixed intervals or triggers (thresholds), and delivers the findings to each user, ready-made. In-aquaculture scoring of behavioral indicators of aquatic animal welfare is challenging, but the increasing availability of low-cost technology now makes the automated monitoring of behavior feasible.Crustacean farming is a fast-growing sector and has contributed to improving incomes. Many studies have focused on how to improve crustacean production. Information about crustacean behavior is important in this respect. Manual methods of detecting crustacean behavior are usually infectible, time-consuming, and imprecise. Therefore, automatic growth situation monitoring according to changes in behavior has gained more attention, including acoustic technology, machine vision, and sensors. This article reviews the development of these automatic behavior monitoring methods over the past three decades and summarizes their domains of application, as well as their advantages and disadvantages. Furthermore, the challenges of individual sensitivity and aquaculture environment for future research on the behavior of crustaceans are also highlighted. Studies show that feeding behavior, movement rhythms, and reproduction behavior are the three most important behaviors of crustaceans, and the applications of information technology such as advanced machine vision technology have great significance to accelerate the development of new means and techniques for more effective automatic monitoring. However, the accuracy and intelligence still need to be improved to meet intensive aquaculture requirements. Our purpose is to provide researchers and practitioners with a better understanding of the state of the art of automatic monitoring of crustacean behaviors, pursuant of supporting the implementation of smart crustacean farming applications.

Can the toxicity of polyethylene microplastics and engineered nanoclays on flatfish (Solea senegalensis) be influenced by the presence of each other?

Microplastics and nanomaterials are applied in a myriad of commercial and industrial applications. When leaked to natural environments, such small particles might threaten living organisms' health, particularly when considering their potential combination that remains poorly investigated. This study investigated the physiological and biochemical effects of polyethylene (PE; 64-125 μm in size, 0.1, 1.0, and 10.0 mg·L−1) single and combined with an engineered nanomaterial applied in antifouling coatings, the copper-aluminium layered double hydroxides (Cu-Al LDH; 0.33, 1.0, and 3.33 mg·L−1) in the flatfish Solea senegalensis larvae (8 dph) after 3 h exposure, in a full factorial design. Particles ingestion, histopathology, and biochemical biomarkers were assessed.Fish larvae presented <1 PE particles in their gut, independently of their concentration in the medium. The histological health index showed minimal pathological alterations at PE combined exposure, with a higher value observed at 1 mg LDH·L−1 × 0.1 mg PE·L−1. Gut deformity and increased antioxidant defences (catalase), neurotransmission (acetylcholinesterase), and aerobic energy production (electron transport system) were observed at PE ≥ 1.0 mg·L−1. No oxidative damage (lipid peroxidation) or alterations in the detoxification capacity (glutathione-S-transferase) was observed on single and combined exposures. PE, combined or not with Cu-Al LDH, does not seem to compromise larvae's homeostasis considering levels reported so far in the marine and aquaculture environments. However, harsh effects are expected with MP contamination rise, as projections suggest.

Insights into the molecular interaction between poly(vinylpyrrolidone)-iodine disinfection system and polypropylene microplastics in aquatic environment

Microplastics (MPs) as emerging contaminants may not only act as an extra compartment for partitioning of disinfectant but also greatly affect the bactericidal power of disinfection agents. This is the first study to investigate the interaction of MPs with poly(vinylpyrrolidone)-iodine (PVP-I) disinfection system, particularly associated with the identification and characterization of the iodine species at molecular level. The results showed that the presence of MPs increased the loss of triiodide ion (I3−) in PVP-I system, which was even accelerated upon oxygen exposure. An obvious blue shift from 1714 to 1665 cm−1 at the vibrational band was observed for iodine-soaked MPs, which was resulted from the hydrogen bonding interaction as one of potential adsorption mechanisms. The interaction resulted in the affinity of polyiodide ions (I3− and I5−) in PVP-I system to MPs as foreign objects, thereby impairing the bactericidal power of PVP-I system. More evident loss of I3− in aged MP suspension was observed compared to pristine MP suspension, suggesting the enhanced interaction of PVP-I system with aged MPs. The interaction was weakened in aquaculture water, due to the photosensitive substances and alkaline condition. These findings confirmed that the interaction between polyiodide ions (I3− and I5−) and MPs in form of hydrogen bond reduced the bactericidal power of PVP-I disinfection system. This study provides a comprehensive insight in to the mechanisms involved in the interaction between MPs and PVP-I disinfection system, and would be helpful for evaluating the environmental behavior of MPs and the bactericidal power of the PVP-I system upon MP exposure in aquaculture environment.

Environmental impacts of microplastics on fishery products: An overview

Plastic particles <5 mm in size, microplastics (MPs), are a global environmental contamination, widely distributed in the environment. Aquaculture environment may have high MPs contamination due to heavy use of plastic equipment. In aquaculture systems, MPs are readily ingested by aquatic organisms and transfer to higher trophic levels such as human through the food web, thereby posing a potential threat to human health. Therefore, controlling MPs pollution has become a hot topic in recent years. This paper systematically summarized the source of MPs, the state of MPs pollution, and the pathway of MPs to food chain such as ingestion. In addition, this study also showed that MPs can adsorb and accumulate pollutants (e.g., persistent organic pollutants, heavy metals and other toxins) from surrounding aquaculture environment and can act as vectors for transfer of these contaminations. The adverse impacts of MPs associated with other toxic chemicals in aquaculture organisms and potential health threat to human are discussed. Finally, some recommendations for future directions are proposed based on current knowledge gaps. In summary, this study emphasizes the impacts of MPs pollution in aquaculture system, especially the ecological effects on aquaculture organisms and associated human health.

Microbial analysis reveals the potential colonization of pathogens in the intestine of crayfish (Procambarus clarkii) in traditional aquaculture environments

The microbiota of the intestine produces a wide array of biologically active molecules and together act as a composite endocrine organ. Due to our limited understanding of bacterial communities in aquaculture ecosystems, it is necessary to evaluate the interactions between environmental and intestinal microbiota and the potential consequences of disease. This study taken the traditional P. clarkii culture in the Sichuan Basin as an example, and analyzed the relationships between the microbiota of the environment and host through microbial analysis and microbiological diagnosis. Our results showed that the bacterial abundance in sediment was greater than in water, followed by the intestine, and some of bacteria from the environment successfully selected to colonize the intestine. The bacterial composition in the intestines of diseased and healthy crayfish was significantly different. The bacteria that colonized and proliferated in the intestine had very low abundances in sediment and water. Two potential pathogens, Aeromonas veronii, and Citrobacter freundii, and two potential probiotics, Lactococcus garvieae and Exiguobacterium undae, were identified. Using multiple, real, and traditional P. clarkii aquaculture sites in the Sichuan Basin, this study revealed that the microbial communities of the environment and animal host did indeed interact. Furthermore, these results indicated that P. clarkii in a healthy status are capable of regulating which bacteria colonize their intestines.

Characterization of ammonia remover Bacillus albus (ASSF01) in terms of biofilm-forming ability with application in aquaculture effluent treatment.

Presence of higher concentration of ammonia (> 0.5 mg/L) as well as nitrite (> 0.2 mg/L) in aquaculture environment create difficulties for fish survival. The existing methods for removal of these pollutants are time-consuming. A stable biofilm-based system for ammonia removal from aquaculture wastewater was developed in the current study to overcome the limitations of conventional treatment processes. In order to do so, initially the bacterial candidate was well characterized and tested for rapid biofilm development. The ammonia bioremediating Bacillus albus (ASSF01), from the activated sludge of shrimp farm, with a generation time of 67 min 12 s in suspension culture, was a structured biofilm former. The staining based measurement showed biofilm initiation from the very first hour of incubation. This finding was further validated using scanning electron microscopy (SEM), profilometry, and ellipsometry with Brewster angular microscopy (BAM). Hurst exponent (H) calculation using the profilometer and ellipsometer data yielded a value of H of above 0.9 and 0.62, indicating positive correlation or persistence behavior, hence a stable biofilm former. Each method of biofilm measurement, in spite of variation in complexity and sensitivity, was equally effective for biofilm progression analysis. The generation time of ASSF01 upon immobilization was 15 min and 36 s, ensuring rapid development of stable system. Response surface methodology (RSM)-based optimization of aquaculture wastewater treatment by the isolate in a biofilm reactor at ambient temperature revealed the optimum influent concentration of ammonia (3.2 mg/L), nitrate (6.89 mg/L), and phosphate (1.17 mg/L) to be reduced to discharge level (as per aquaculture requirement) with 14 h of hydraulic retention time. This study demonstrates the potential of the isolate as an efficient bioremediant for treating ammonia-containing aquaculture wastewater in a single unit biofilm reactor, ensuring rapid stabilization, environmental protection, and aquaculture sustenance.

Antibiotic Resistance Profiles and Molecular Characteristics of Extended-Spectrum Beta-Lactamase (ESBL)-Producing Escherichia coli and Klebsiella pneumoniae Isolated From Shrimp Aquaculture Farms in Kerala, India.

This study was undertaken to evaluate the prevalence of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae in selected shrimp aquaculture farms (n = 37) in Kerala, South India and to characterize the isolates using molecular tools. Overall, a low prevalence of ESBL-producers was found in the farms, most likely due to the reduced antibiotic usage in the shrimp farming sector. Out of the 261 samples (77 shrimp and 92 each of water and sediment), 14 (5.4%) tested positive for ESBL-E. coli or ESBL-K. pneumoniae. A total of 32 ESBL-E. coli and 15 ESBL- K. pneumoniae were recovered from these samples. All ESBL isolates were cefotaxime-resistant with minimal inhibitory concentration (MIC) ≥32 μg/ml. Of all isolates, 9 (28.1%) E. coli and 13 (86.7%) K. pneumoniae showed simultaneous resistance to tetracycline, ciprofloxacin, and trimethoprim-sulfamethoxazole. PCR analysis identified CTX-M group 1 (blaCTX–M–15) as the predominant ESBL genotype in both E. coli (23, 71.9%) and K. pneumoniae (15, 100%). Other beta-lactamase genes detected were as follows: blaTEM and blaSHV (11 K. pneumoniae), blaCTX–M group 9 (9 E. coli), and blaCMY–2 (2 E. coli). Further screening for AMR genes identified tetA and tetB (13, 40.6%), sul1 (11, 34.4%), sul2 (9, 28.1%), catA and cmlA (11, 34.4%), qepA and aac(6′)-Ib-cr (9, 28.1%) and strAB and aadA1 (2, 6.3%) in E. coli, and qnrB (13, 86.7%), qnrS (3, 20%), oqxB (13, 86.7%), tetA (13, 86.7%), and sul2 (13, 86.7%) in K. pneumoniae isolates. Phylogenetic groups identified among E. coli isolates included B1 (4, 12.5%), B2 (6, 18.8%), C (10, 31.3%), D (3, 9.4%), and E (9, 28.1%). PCR-based replicon typing (PBRT) showed the predominance of IncFIA and IncFIB plasmids in E. coli; however, in K. pneumoniae, the major replicon type detected was IncHI1. Invariably, all isolates of K. pneumoniae harbored virulence-associated genes viz., iutA, entB, and mrkD. Epidemiological typing by pulsed-field gel electrophoresis (PFGE) revealed that E. coli isolates recovered from different farms were genetically unrelated, whereas isolates of K. pneumoniae showed considerable genetic relatedness. In conclusion, our findings provide evidence that shrimp aquaculture environments can act as reservoirs of multi-drug resistant E. coli and K. pneumoniae.

Comparative transcriptomic analysis reveals the molecular mechanisms related to oxytetracycline- resistance in strains of Aeromonas hydrophila

Antibiotic resistance among aquatic bacterial pathogens has become a serious concern in aquaculture environments, which has increased research interest to develop solutions to overcome this problem. Moreover, the activities of several Aeromonas hydrophila gene pathways have remained elusive concerning antibiotic resistance evolution. Therefore, in this study, we have performed a transcriptomic analysis to compare differentially expressed genes between oxytetracycline (OXY) susceptible and resistant strains of A. hydrophila. Compared to the A. hydrophila susceptible strain, a total of 22 and 185 genes were differentially expressed in the 4-fold minimal inhibitory concentration (MIC) and 8-fold MIC resistant strains, respectively. Furthermore, the bioinformatics analysis revealed that the sulfur metabolism-related genes were down-regulated. The genes responsible for mannitol metabolism and the efflux pump system were up-regulated in resistant strains, compared to the susceptible strain. Therefore, it suggests that these three pathways may be involved in the OXY resistance evolution in A. hydrophila. The outcome of the transcriptomic data was further validated through quantitative reverse transcription-PCR (qRT-PCR) and Western blot analysis. Overall, the obtained data provides a deeper insight into the intrinsic molecular mechanism of OXY resistance evolution in A. hydrophila.

Metagenomics reveals the taxonomy and resistance mechanism of antibiotic resistance genes in bacterial communities of an aquaculture pond

In order to reveal the distribution characteristics of antibiotic resistance genes (ARGs) in freshwater aquaculture ponds, the microbial composition and antibiotic resistance gene types in the aquaculture environment were analyzed by using high-throughput and metagenomics sequencing technology. Our results showed that there were significant differences in the dominant bacteria composition in the water and sediment of aquaculture ponds. The dominant phylum in aquaculture water was Actinobacteria, Proteobacteria, Cyanobacteria and Bacteroidetes, while the phylum Actinobacteria, Chloroflexi and Proteobacteria were enriched in sediment. Compared with the comprehensive antibiotic research database (CARD), a total of 187 ARGs were identified, which were mainly multidrug, MLS and Tetracycline antibiotic resistance genes. There were 5 resistance mechanisms in the aquaculture environment, of which antibiotic efflux was the main resistance mechanism. Correlation analysis between ARGs and microbes showed that the abundance of Bacteroidetes, Cyanobacteria and Chloroflexi significantly affected the abundance of major resistance genes. This study is of great significance to protect the micro-environment of aquaculture ponds and control the pollution and spread of ARGs.

Distribution and antimicrobial resistance of Vibrio parahaemolyticus isolated from fish and shrimp aquaculture farms along the Korean coast

The present study investigated the distribution and antimicrobial susceptibility patterns of Vibrio parahaemolyticus in water samples and aquatic animals (fish and shrimp) from major aquaculture farms along the Korean coast in 2018. V. parahaemolyticus is the most common pathogen causing seafood-borne illness. The strain was detected in 34.7% of all samples tested, and was detected at higher levels during summer to autumn when the water temperature is higher. Although more than 90.0% of V. parahaemolyticus isolates were sensitive to 13 of the 15 antimicrobials tested, which is useful for treating V. parahaemolyticus infectious disease, the isolates exhibited higher resistance to two antibiotics (colistin and ampicillin), which should be excluded as treatment options for these infections. Koreans typically enjoy consuming raw seafood. To reduce the potential human health risk of raw seafood consumption, the prevalence and antimicrobial resistance of V. parahaemolyticus in aquaculture environments should be continuously valuated.

Sources, distribution and dynamics of antibiotics in Litopenaeus vannamei farming environment

In aquaculture, antibiotics are often added to the feeds to prevent and treat bacterial diseases. Antibiotic residues in aquaculture environment can be altered by the feeds introduced in different farming phases. Currently, less information is available on the distribution and dynamics of antibiotic residues in aquaculture environment during a farming cycle. In this study, we investigated the sources, distribution, and dynamics of selected 12 antibiotics in pond water, sediment, and shrimp muscles during a whole whiteleg shrimp (Litopenaeus vannamei) farming cycle. The results showed that a total of 6 antibiotics were detectable in pond water. Oxytetracycline (OTC) and sulfamethoxazole (SMX) were the main antibiotic residues and found in all pond water samples. The total antibiotic residues in the pond water was temporarily decreased from 55.5 ng/L in phase of shrimp larvae to 33.0 ng/L in phase of juvenile shrimp, and then gradually increased to 64.4 ng/L in the later phase of mature shrimp. In the sediment, 8 of 12 antibiotics were detectable and the total amount of antibiotic residues was gradually accumulated during cultivation. The total concentration of 8 antibiotics in sediment increased nearly 5 times by comparing to the background concentration before shrimp larvae was introduced in the system. In shrimp muscle, 6 antibiotics were accumulated from juvenile shrimp (total antibiotics = 41.8 μg/kg) to mature shrimp (total antibiotics = 134 μg/kg) phase. SMX, OTC, and levofloxacin (LEOF) are the main antibiotic residues found in shrimp muscle. Pearson correlation analyses showed that the dynamics of antibiotics in sediment and shrimp muscle were significantly correlated with antibiotics found in feeds, indicating that feed is an important source of antibiotic residues accumulated in aquatic organism and sediment. Dietary exposure assessment indicated that the exposure risk of the selected antibiotics in shrimp muscle for human health were negligible.

Assessment of total bacterial diversity in whiteleg shrimps and its aquaculture environment in Pangkajene and Banyuwangi, Indonesia

Detection of bacterial diversity in whiteleg shrimps and its rearing water is a vital first step in monitoring aquaculture activities. Bacterial community imbalance in whiteleg shrimps and its rearing water influences the quality and quantity of shrimp production. Identifying the bacterial community provides basic information related to dominant bacterial groups in whiteleg shrimps and environments, providing recommendations for proper environmental monitoring and management. In this study, we investigated bacterial community structure in the rearing water and intestinal tract of whiteleg shrimp (Litopenaeus vannamei) collected from two sites, i.e., Pangkajene, South Sulawesi (SU) and Banyuwangi, East Java (BW), Indonesia. The bacterial community was analyzed using amplicon sequencing with Illumina sequencing platform based on the V3-V4 region of the 16S rRNA genes. Bacterial diversity and composition were found differed between the rearing water and the shrimps’ intestines. Bacterial diversity in the rearing water of Banyuwangi (W.BW) was higher than that of Pangkajene (W.SU). Proteobacteria, Bacteroidetes, and Firmicutes were found as the most dominant phyla in rearing water from both farms, while distinct bacterial composition was observed in the shrimps’ intestines. The shrimp intestine from Banyuwangi (U.BW) was dominated by Firmicutes (22.36%), Proteobacteria (22.33%), and Verrucomicrobia (21.11%). In contrast, the shrimp intestine from Pangkajene (U.SU) was highly dominated by Tenericutes (88.54%), followed by Proteobacteria (4.66%), and Firmicutes (2.27%). The difference in bacterial community structure between the rearing water and shrimps’ intestines suggested that the host intestinal environment might have greater selective pressure for bacterial composition inhabiting L.vannamei intestines. Our observations suggest that the shrimps cultured in the rearing water with the similar dominant bacterial group have specific intestinal bacterial diversity.

Potensi Pengembangan Budidaya Pada Kawasan Konservasi Perairan Datok Bandar Kabupaten Lingga

The development of aquaculture in the Marine Protected Area (KKP) has to recognize the sustainability and the balancing of the ecosystem in that area. It causes limited rights of users who want to develop their business, where the issuance of permits and business management regulations is an obligation that must be followed by aquaculture business developers in the KKP area. The study aimed was to formulate the technical directions in developing the potential for aquaculture business in the Marine Protected Area of Datok Bandar (KKPD) at Lingga Regency. The method used in this research is a descriptive quantitative using analysis of the carrying capacity of the environment for aquaculture, water quality parameters, and a participatory approach. The results showed that the potential area to be developed for aquaculture was 3,736.01 ha. However, based on the carrying capacity analysis, only 268,420 ha or 7.2% from the existing potential can be utilized for aquaculture. Furthermore, based on the water quality measurements for aquaculture, the KKPD area was divided into 3 designations groups of aquaculture areas, namely the KJT, KJA, and seaweed. The number of aquaculture business units that were allowed in this area was 16,776 units consisting of 10,066 small business units and 6,710 medium business units with 7 types of superior fish. The limitation of land area and some business units in conservation areas were important to ensure the sustainability of the environment in the future. The implication of this research could be used as a basis for issuing aquaculture business permits, and to ensure that small-scale aquaculture fishermen have a large proportion. In addition to ensuring the existence of local communities who were generally small farmers, conservation areas were very vulnerable to environmental changes, so the risk factors and impacts of business utilization were important to consider.

The Gut Microbiota of Naturally Occurring and Laboratory Aquaculture Lytechinus variegatus Revealed Differences in the Community Composition, Taxonomic Co-Occurrence, and Predicted Functional Attributes

Sea urchins, in many instances, are collected from the wild, maintained in the laboratory aquaculture environment, and used as model animals for various scientific investigations. It has been increasingly evident that diet-driven dysbiosis of the gut microbiome could affect animal health and physiology, thereby impacting the outcome of the scientific studies. In this study, we compared the gut microbiome between naturally occurring (ENV) and formulated diet-fed laboratory aquaculture (LAB) sea urchin Lytechinus variegatus by amplicon sequencing of the V4 region of the 16S rRNA gene and bioinformatics tools. Overall, the ENV gut digesta had higher taxa richness with an abundance of Propionigenium, Photobacterium, Roseimarinus, and Flavobacteriales. In contrast, the LAB group revealed fewer taxa richness, but noticeable abundances of Arcobacter, Agarivorans, and Shewanella. However, Campylobacteraceae, primarily represented by Arcobacter spp., was commonly associated with the gut tissues of both ENV and LAB groups whereas the gut digesta had taxa from Gammaproteobacteria, particularly Vibrio spp. Similarly, the co-occurrence network displayed taxonomic organizations interconnected by Arcobacter and Vibrio as being the key taxa in gut tissues and gut digesta, respectively. Predicted functional analysis of the gut tissues microbiota of both ENV and LAB groups showed a higher trend in energy-related metabolisms, whereas amino acids, carbohydrate, and lipid metabolisms heightened in the gut digesta. This study provides an outlook of the laboratory-formulated diet-fed aquaculture L. variegatus gut microbiome and predicted metabolic profile as compared to the naturally occurring animals, which should be taken into consideration for consistency, reproducibility, and translatability of scientific studies.

Antibiotic accumulation, growth performance, intestinal diversification, and function of Nile tilapia (Oreochromis niloticus) feed by diets supplemented with different doses of sulfamethoxazole.

To comprehensively investigate the effects of exposure to legal doses of sulfamethoxazole (SMZ) in Nile tilapia (Oreochromis niloticus), fishes were exposed to diets supplemented with different doses of SMZ (NS, normal feed; LS, 20 mg/kg·day; MS, 200 mg/kg·day; and HS, 1000 mg/kg·day) for 4 weeks and then fed with normal feed for 4 weeks. General SMZ accumulation, growth performance, intestinal short-chain fatty acids, intestinal flora diversity, composition, and function were systemically evaluated. Results indicated that the SMZ accumulation in O. niloticus muscles, intestinal contents, and aquaculture environment positively correlated to the exposure dose. The growth performance, measured by weight increase, was MS>LS>NS, while HS antibiotics retarded the growth. SMZ-exposed O. niloticus had an increased number of fat particles in the liver and a change in the content of intestinal SCFAs. Moreover, SMZ exposure changed the biological diversity of the intestinal flora and subsequently induced microbiota dysbiosis, primarily inhibiting the growth of Fusobacteria, especially in HS group. Overall, exposure to higher SMZ doses than the recommended ones impair general intestinal functions and provokes health risk in fish. This study highlights the importance of rational and regulated use of SMZ in aquaculture.

Metal contamination and coexistence of metal and antibiotic resistance in Vibrio species recovered from aquaculture ponds with and without history of antibiotic usage in Southwest Nigeria

BackgroundThe use of metal-containing and antimicrobial compounds is a common practice in aquaculture operations in Nigeria. Only a few studies have focused on the impact of these chemicals on metal and antibiotic resistance development in the bacterial flora of aquaculture. This study therefore sets out to fill this gap.ResultsFive metals, namely copper (Cu), zinc (Zn), lead (Pb), nickel (Ni) and chromium (Cr), were detected at different concentrations in the pond water samples, with most values obtained exceeding the maximum recommended national standard for fisheries and recreation water quality criteria set by the National Environmental Standards and Regulations Enforcement Agency (NESREA) in Nigeria. A total of 121 Vibrio spp. were recovered from the aquaculture pond water with Vibrio cholerae having the highest frequency (37) followed by Vibrio parahaemolyticus (36), Vibrio vulnificus (36) and Vibrio alginolyticus (12). Seventy-five isolates were recovered from ponds with history of antibiotic use, while the ponds with no recognized history of antibiotic use had forty-six isolates. The percentage resistance to antibiotics in the isolates was: ampicillin (88.5%), amoxicillin–clavulanate (44.3%), tetracycline (41%), trimethoprim-sulfamethoxazole (22.1%), chloramphenicol (15.6%), ciprofloxacin (11.5%), imipenem (5.7%), ceftazidime (4.1%) and gentamicin (0%). All the isolates tolerated all the metals to 400 µg/mL concentration while only the trio of Pb, Ni and Cr were tolerated beyond the concentration. Zn and Cu appeared to be the most toxic metals on Vibrio spp., with no isolate surviving beyond the 400 µg/mL concentration mark, while 57 of the 121 isolates survived Cr at the highest concentration (3200 µg/mL), making it the most tolerated of the metals.ConclusionThis study reports a high level of metal contamination in the aquaculture ponds studied. The concentration of the metals exceeded the maximum permissible limits in Nigeria. Also, there was coexistence of metal and antibiotic resistance in the bacteria recovered from the aquaculture ponds. There is a need to regulate the use of chemicals, especially antibiotics and some biocidal compounds, to clamp down on the introduction of metals and antibiotics into the aquaculture systems, as these chemicals could facilitate the development of resistance traits in aquaculture bacteria by creating a selective pressure in the aquaculture environment.

Metagenomics and Other Omics Approaches to Bacterial Communities and Antimicrobial Resistance Assessment in Aquacultures.

The shortage of wild fishery resources and the rising demand for human nutrition has driven a great expansion in aquaculture during the last decades in terms of production and economic value. As such, sustainable aquaculture production is one of the main priorities of the European Union’s 2030 agenda. However, the intensification of seafood farming has resulted in higher risks of disease outbreaks and in the increased use of antimicrobials to control them. The selective pressure exerted by these drugs provides the ideal conditions for the emergence of antimicrobial resistance hotspots in aquaculture facilities. Omics technology is an umbrella term for modern technologies such as genomics, metagenomics, transcriptomics, proteomics, culturomics, and metabolomics. These techniques have received increasing recognition because of their potential to unravel novel mechanisms in biological science. Metagenomics allows the study of genomes in microbial communities contained within a certain environment. The potential uses of metagenomics in aquaculture environments include the study of microbial diversity, microbial functions, and antibiotic resistance genes. A snapshot of these high throughput technologies applied to microbial diversity and antimicrobial resistance studies in aquacultures will be presented in this review.

Drag and inertia coefficients of live and surrogate shellfish dropper lines under steady and oscillatory flow

Against the background of a drastically increased demand of marine proteins, off-bottom, bivalve aquaculture, provides significant potential for production growth when moved into more energetic marine waters. Hence, research, industry and politics are currently proposing the development of new offshore sites. The highly energetic conditions at these sites present a challenging environment for bivalve aquaculture. In this work, physical experiments of suspended bivalves provide new knowledge on the commonly used design parameters: the drag and inertia coefficients. Live bivalves and manufactured surrogate models at a 1:1 scale were tested in a towing tank as well as under waves. The drag coefficient of live blue mussels was determined to be Cd = 1.6 for Reynolds numbers between 2.3 × 104 and 1.4 × 105. The inertia coefficient obtained from the wave tests was Cm = 2.1 for Keulegan Carpenter numbers KC < 10. In a pursuit to better understand the differences between live mussels and surrogates in laboratory conditions, the analysis revealed that appropriate surrogates can be identified. A method to determine the characteristic diameter of mussel dropper lines is suggested. The results facilitate the future design of aquaculture systems in high-energy environments and allow for an integration into numerical models.

Plasmid-Mediated Antibiotic Resistant Escherichia coli in Sarawak Rivers and Aquaculture Farms, Northwest of Borneo.

Background: The emergence of plasmid-mediated antibiotic resistance in Escherichia coli in water resources could pose a serious threat to public health. The study aims to investigate the dispersion of plasmid-mediated antibiotic-resistant E. coli from six rivers in Sarawak and two aquaculture farms in Borneo. Methods: A total of 74 water samples were collected for the determination of their bacteria colony count. An IMViC test identified 31 E. coli isolates and tested their susceptibility against twelve clinically important antibiotics. The extraction of plasmid DNA was done using alkali lysis SDS procedures. Characteristics, including plasmid copy number, molecular weight size, resistance rate and multiple antibiotic resistance (MAR), were assessed. Results: Our findings revealed that bacterial counts in rivers and aquaculture farms ranged from log 2.00 to 3.68 CFU/mL and log 1.70 to 5.48 cfu/mL, respectively. Resistance to piperacillin (100%) was observed in all E. coli; resistance to amoxicillin (100%) and ampicillin (100%) was observed in E. coli found in aquaculture farms; resistance to streptomycin (93%) was observed in E. coli found in rivers. All E. coli were resistant to ≥2 antibiotics and formed 26 MAR profiles, ranging from an index of 0.17 to 0.83, indicating that there are high risks of contamination. Some (48.4%) of the E. coli were detected with plasmids (1.2 to >10 kb), whereas 51.6% of the E. coli did not harbor any plasmids. The plasmid copy numbers reported were one plasmid (n = 7), two plasmids (n = 4), ≥ two plasmids (4). E. coli isolated from the Muara Tuang River showed the highest-molecular-weight plasmids. A statistical analysis revealed that there is no significant correlation (r = 0.21, p = 0.253) between the number of plasmids and the MAR index of the tested isolates. Conclusion: The distribution of MAR in E. coli from rivers is higher compared to the aquaculture environment. Our study suggests that MAR in isolates could be chromosome-mediated. Our results suggest that riverbed sediments could serve as reservoirs for MAR bacteria, including pathogens, under different climatic conditions, and their analysis could provide information for public health concerns.