Freshwater Aquaculture Systems Research Articles

Climate Change Impacts on Aquaculture Systems in Key Producing Nations: Assessing Vulnerability and Proposing a Novel Adaptation Measure

Climate change poses a significant threat to the aquaculture industry, impacting both the productivity and sustainability of this vital sector. This study focuses on the vulnerability of the top aquaculture producing nations to climate change and explores potential novel adaptation strategy. The vulnerability assessment considered various factors, including the exposure of aquaculture systems to climate change, Productivity of the industry, climate change initiators and the GDP of each nation surveyed. The study identifies the United Kingdom (UK) aquaculture as the most vulnerable and at risk of climate change impacts followed by the United States of America (USA) and Nigeria’s aquaculture. In terms of continents, Europe, Oceania, and Africa are identified as the most vulnerable regions, while America and Asia are considered the least vulnerable. The UK, with its extensive aquaculture operations and geographical exposure to climate change risks, faces significant challenges in adapting to changing conditions especially with the exit from European Union (Brexit). The USA, another major aquaculture producer, also faces vulnerability due to its diverse range of climatic conditions and coastal aquaculture operations. Nigeria, a prominent aquaculture producer in Africa, is highly vulnerable to climate change due to its dependence on freshwater aquaculture systems leading to low water usage in aquaculture despite vast marine water resource. Strict measures including novel adaptation measure such as the NanoSolar technique must be put in place in these countries in other to ensure that aquaculture production doesn’t decline and also to ensure that global food security is not put under pressure with the growing world population size.

Effect of Photoperiod and Transfer Time on Atlantic Salmon Smolt Quality and Growth in Freshwater and Seawater Aquaculture Systems

Smoltification is a key process in Atlantic salmon aquaculture, given it prepares the fish for a successful transit from fresh to seawater. However, industry players have not yet reached a consensus on the best protocols to produce high-quality smolts. In this study, we assessed how the combination of two photoperiod regimes in freshwater (continuous light or LL, and natural photoperiod or LDN) and four transfer times to seawater (February, March, April, and May) affected smolt development and their subsequent growth in seawater until slaughter during commercial production. The results demonstrated that smoltification and growth in freshwater were only slightly modulated by the photoperiod treatment and were instead much more affected by the limiting effect of the low water temperature during that period. In seawater, the growth rate was the highest in the same groups, which had, however, experienced a delay in growth when in freshwater, and consequently, no differences in the final body weight between the eight treatments were found. Such compensatory growth in the sea was probably enhanced by the increasing smolt quality, which could allow for better performance in seawater. A significant link between the weight at slaughter and weight at transfer was observed only in the groups with a lower smolt quality (LL-Feb, LDN-Feb and LDN-Mar), which suggests that larger individuals could cope better with a saline environment. In contrast, smaller smolts probably suffered greater osmotic stress that hindered their performance at sea. Afterwards, as smolt quality increased in the subsequent transfer groups, the relevance of this size effect decreased. This means that the industry may benefit from transferring larger smolts to seawater, especially if these are suspected of having developed suboptimal seawater tolerance. Those individuals are likely to cope better with saline conditions than smaller smolts. Future research should focus on the possible long-term effects of freshwater-rearing regimes on smolt performance in the seawater phase.

Antimicrobial resistome during the transition from an integrated to a monoculture aquaculture farm in southern China

Integrated and monoculture freshwater aquaculture systems are often regarded as important reservoirs for antimicrobial resistance genes (ARGs) and antimicrobial resistance bacteria (ARBs), yet only a few studies have assessed differences in the antimicrobial resistome and antibiotic residues between aquaculture modes. In this study, a metagenomic approach was used to comprehensively explore the dynamic patterns and potential transmission mechanisms of ARGs in ducks, human workers, fish, water and sediments during the transition from an integrated to a monoculture freshwater aquaculture mode and to investigate the associations of ARGs with potential hosts in microbial communities using network analysis and a binning approach. The results showed that the abundance and diversity of ARGs were higher under integrated fish–duck farming than in single fish ponds. During the transition from an integrated to a monoculture aquaculture farm, ARGs in workers and sediments were not easily removed. However, ARGs in the aquatic environment underwent regular changes. In addition, duck manure was probably the most dominant source of ARGs in the duck farm environment. Network analysis indicated that Escherichia spp. were the most dominant hosts of ARGs. Variation partitioning analysis (VPA) showed that in water samples, the bacterial community played an important role in the ARG profile. In addition, we identified a potential risk of the presence of highly virulent and antimicrobial-resistant Klebsiella pneumoniae in workers. These results help assess the risk of ARG transmission in integrated and monoculture aquaculture farms and suggest that we should strengthen the monitoring of long-term resistance in integrated aquaculture environments.

Tetracycline resistance potential of heterotrophic bacteria isolated from freshwater fin-fish aquaculture system

This study investigated the tetracycline resistance potential of heterotrophic bacteria isolated from twenty-four freshwater fin-fish culture ponds in Andhra Pradesh, India. A total of 261 tetracycline resistant bacteria (tetR) were recovered from pond water, pond sediment, fish gills, fish intestine, and fish feed. Bacteria with high tetracycline resistance (tetHR) (n=30) that were resistant to tetracycline concentrations above 128 μg mL-1 were predominantly Lactococcus garvieae followed by Enterobacter spp., Lactococcus lactis, Enterobacter hormaechei, Staphylococcus arlettae, Streptococcus lutetiensis, Staphylococcus spp., Brevundimonas faecalis, Exiguobacterium profundum, Lysinibacillus spp., Stutzerimonas stutzeri, Enterobacter cloacae, and Lactococcus taiwanensis. Resistance to 1024μg mL-1 of tetracycline was observed in L. garvieae, S. arlettae, Enterobacter spp., B. faecalis. Tet(A) (67%) was the predominant resistance gene in tetHR followed by tet(L), tet(S), tet(K), and tet(M). At similar concentrations of exposure, tetracycline procured at the farm level (69.5% potency) exhibited lower inhibition against tetHR bacteria compared to pure tetracycline (99% potency). The tetHR bacteria showed higher cross-resistance to furazolidone (100%) followed by co-trimoxazole (47.5%) and enrofloxacin (11%). The maximum threshold of tetracycline resistance at 1024μg mL-1 was observed in S. arlettae, Enterobacter spp., B. faecalis, and L. garvieae and tet(A) was the major determinant found in this study.

Remediation and recovery of Kariba weed as emerging contaminant in freshwater and shellfish aquaculture system via solvothermal liquefaction

Fast growing Kariba weed causes major problems and pollution on freshwater and shellfish aquaculture systems by interfering with nutrient uptake of crops, restricting sunlight penetration, and decreasing water quality due to massive biomass of Kariba weed remnants. Solvothermal liquefaction is considered an emerging thermochemical technique to convert waste into high yield of value-added products. Solvothermal liquefaction (STL) of Kariba weed as an emerging contaminant was performed to investigate the effects of different types of solvents (ethanol and methanol) and Kariba weed mass loadings (2.5–10 % w/v) on treating and reducing the weed via conversion into potentially useful crude oil product and char. Up to 92.53 % of Kariba weed has been reduced via this technique. The optimal conditions for crude oil production were found to be at 5 % w/v of mass loading in methanol medium, resulting in a high heating value (HHV) of 34.66 MJ/kg and yield of 20.86 wt%, whereas the biochar production was found to be optimum at 7.5 % w/v of mass loading in methanol medium, resulting in 29.92 MJ/kg of HHV and 25.38 wt% of yield. The crude oil consisted of beneficial chemical compounds for biofuel production such as hexadecanoic acid, methyl ester (65.02 peak area %) and the biochar showed high carbon content (72.83 %). In conclusion, STL as a remediation for emerging Kariba weed is a feasible process for shellfish aquaculture waste treatment and biofuels production.

Using The Thick-Shelled River Mussel (Unio crassus) Filtering Ability for Water Treatment Process in Aquaculture Systems: an In Vitro Study on Removal of the Bacteria from The Water

The thick-shelled river mussel (Unio crassus) is listed as 'Endangered' on the IUCN Red List of Threatened Species and it is important to culture them for the conservation of natural stocks. Integrating mussels into the freshwater aquaculture system could be an efficient method, because of their filtering ability. In this study, it was aimed to determine the bacteria filtering ability of the thick-shelled river mussel on an aquaculture system to determine if the water quality got better in terms of bacteriology. Depuration, disinfection, and antibiotic treatments were applied to reduce the bacterial load in the mussels' bodies. Disinfection was made using NaCl2 , 2-Phenoxyethanol, Formalin, Virkon® S and Chloramine T. Antibiotic treatment was performed using Oxytetracycline and Florfenicol. The best result was obtained in the group to which 5 mg L-1 Oxytetracycline was added. However, since mussels can uptake the same bacteria into own bodies with their own pseudofeces, it was found that it is appropriate to use antibiotic treatment and depuration applications together. In the experiment of keeping them in the same environment with the pathogens (Staphylococcus epidermidis, Aeromonas caviae), intense growth of bacteria was inoculated into water. Thus, it has been determined that mussels clean the water by removing bacteria from the environment within 48 hours, so river mussels can be adapted to aquaculture systems to reduce aquatic bacteria.

Aquaculture farm largely increase indirect nitrous oxide emission factors of lake

Freshwater aquaculture system is one of the main sources of nitrous oxide (N2O) and must be accounted for when reporting indirect N2O emissions from agricultural industries. The IPCC based approach recommend the indirect N2O emission factors (EF5) to estimate the emissions from freshwater. Unfortunately, the EF5 for lake aquaculture, one of the most common freshwater aquacultures, has never been reported due to the scarcity of field data. To better understand the magnitude of EF5 at lake aquaculture and identify the control factors, the EF5 at aquaculture farm and open water (non-aquaculture region) of Lake Taihu were investigated based on long-term (2012–2017) in-situ field measurements. Our results showed the indirect N2O emission at the aquaculture farm (1.52 ± 0.49 μmol m-2 d-1) was over one order of magnitude higher than at the open water (0.12 ± 0.49 μmol m-2 d-1). Furthermore, we also found large variability in the EF5, which varied by one order of magnitude across time. The EF5 was predicted by nitrogen and the mass ratio of carbon to nitrogen. The significantly higher mass ratio of DOC to DIN resulting from feed application contributed to substantial increase in the N2O production efficiency and EF5 at the aquaculture farm. The average EF5 at the aquaculture farm and open water were 0.0021 ± 0.0013 and 0.0013 ± 0.0010, respectively. However, the measured EF5 was lower than that IPCC’s default value of 0.0025, implying IPCC method yielded the overestimated indirect emission, and large bias will occur when only use constant value considering the dramatic variability of observed EF5.

The underestimated importance of fertilizer in aquacultural phosphorus budget: Case of Chinese mitten crab

China's reliance on aquaculture has intensified to satisfy the growing human demand for high-quality animal protein, making it the only country whose aquaculture production has greatly exceeded that of capture fishery for a long time. Previous studies have shown that phosphorus (P) is a limiting nutrient for freshwater eutrophication; therefore, the quantification of P flows in freshwater aquaculture is of great importance for improving aquaculture efficiency and reducing environmental pollution. In this study, life cycle assessment (LCA) and substance flow analysis (SFA) are combined to develop a life cycle P flow model for Chinese mitten crab (Eriocheir sinensis) culture and calculate the P inputs, outputs and net change in stock. The results show a relatively low P use efficiency (4 %) in Chinese mitten crab. Among all life-cycle stages, the maximum P input occurs during adult crab cultivation, when feed is continuously added to maintain appropriate nutrition levels and increase body weight. In addition, fertilizer is often neglected in the existing accounts but accounts for 24 % of the total P inputs. On the output side, approximately 86 % of the P accumulates in sediment, indicating the potential of sediment recycling as a nutrient source in agriculture. This study provides an updated quantitative method for describing nutrient flows within freshwater aquaculture systems and will contribute to decision-making in pollution control of intensive freshwater aquaculture activities.

Occurrence of microplastics within a freshwater aquaculture system in the Pacific Islands, Viti Levu, Fiji

Microplastics (MPs) have become frequent topics of research within Pacific Islands (PIs) in recent years; however, within PI freshwater aquaculture systems, MPs have not yet been quantified. As such this study is aimed at quantifying and characterizing the MP load from across a freshwater aquaculture system within Fiji. Water, sediment, and fish samples were collected from various stages between water source and drainage channels of an aquaculture facility in Navua, Fiji. MPs were extracted using established protocols and analyzed for abundance, form type, size, and polymer composition. Results show no significant difference in MP abundance between sampling sites for, water (average: 3.2 ± 1.14 MP/L), sediment (average: 2.3 ± 0.7 MP/100g DW), and fish (average: 2.7 ± 1.4 MP/fish). Fibers were the most frequent form type in all three elements (average: 2.9 ± 0.2 MP/L in water, 2.1 ± 0.75 MP/100g DW, 2.8 ± 0.14 MP/fish); however, the difference across sites was significant within water samples only. In water and sediments, smaller MPs (< 1.4mm) were the most frequent comprising > 35% in all three elements; however, the difference was not significant between sites. Polymer analysis found that polypropylene, polyurethane, and nylon were the most abundant polymers, which coupled with observed form type and size characteristics suggest a common sources of MPs across sites.

Advances in Ecology Research on Integrated Rice Field Aquaculture in China

Integrated rice field aquaculture, a practice normally used by rural small-scale farmers, is not only supporting farms and livelihoods but is also reducing poverty and is playing a more and more important role in China. It is also becoming one of the main freshwater aquaculture systems, in addition to ponds, lakes, reservoirs, streams, and other aquaculture systems. During the past 40 years, both the production and areas of integrated rice field aquaculture in China have significantly increased from 0.13 million t and 0.74 million ha in 1990 to 3.25 million t and 2.56 million ha in 2020, respectively. Advances in ecology research on integrated rice–fish aquaculture were one of the main contributors to this achievement. In this paper, we systematically reviewed the advances in ecology research on three major integrated rice field aquaculture systems in China, namely rice–fish, rice–crab, and rice–crayfish coculture systems, the contribution of the research, and future prospects. We found that progress in ecology research on theories, biological studies, models, and eco-engineering techniques, coupled with policy support promoted the development of the rice field aquaculture industries. This review could assist individual small-scale farmers to make better use of rice field space to produce safer aquatic and rice products at a lower cost and help aquaculture scientists to further study the ecology of integrated rice field aquaculture systems.

Transcriptome analysis revealed hub genes for muscle growth in Indian major carp, Catla catla (Hamilton, 1822)

Catla (Catla catla) is the fastest growing Indian major carp species and forms an important component of the freshwater aquaculture systems in the Indian sub-continent. The molecular mechanisms of growth of the species in response to seasonal water temperature variations hitherto are still unknown. In the current study, high-throughput transcriptome sequencing was used to study the differential gene expression pattern in catla muscle tissues between pre-winter and post-winter fingerling groups and fast-growing table size fish. Transcriptome analysis identified 1677 differentially expressed genes (DEGs) in three different growth stages and 236 common DEGs between fingerling at low temperature and table fish post-winter, including four genes under GH/IGF1 axis and 163 genes under signature for compensatory muscle growth. Molecular pathways for the mapped genes identified 42 KEGG pathways and the critical pathways under Environmental Information Processing identified were PI3K-Akt signaling, AMPK signaling pathway, Calcium signaling pathway and MAPK signaling pathway. In this study, 14 differentially expressed potential regulatory hub genes for growth were identified, for the first time and categorized into three major GO groups: unfolded protein binding, rNA processing and biogenesis and muscle development and differentiation. These regulatory hub genes, except acta1, were found to be upregulated in fast-growing table size and post-winter fingerling groups. The results provided valuable information about the key genes, with potential to be used as biomarkers of growth in breeding programs and contributed to our understanding of the molecular mechanisms and pathways regulating muscle growth, in response to temperature fluctuations and different growth stages in C. catla.

Characteristics of Chromophoric Dissolved Organic Matter (CDOM) Produced by Heterotrophic Bacteria Isolated from Aquaculture Systems

Heterotrophic bacteria (HB) play an important role in aquatic ecosystems as recyclers of dissolved organic matter (DOM). The objective of this study was to characterize the spectral characteristics of intracellular (IC), and extracellular (EC) compounds produced by 12 HB isolated from two aquaculture systems. Microorganisms belonging to the genera Bacillus, Paenibacillus, and Psychrobacillus were identified by analysis of the 16S ribosomal gene. Aliquots of bacterial culture were centrifugated every hour (1st to 7th) to obtain the EC compounds. The pellet was ultrasound-lysed to obtain the IC compounds. Excitation-emission matrices were used in combination with parallel factor analysis (PARAFAC) to characterize the fluorescent components of DOM (FDOM). PARAFAC indicated two protein-like components and two humic-like components in both cell spaces. At the IC, B. macquariensis showed a high fluorescence index (FI), probably associated with fulvic acid, quinones, or ketones. Psychrobacillus insolitus showed an inverse correlation between spectral slopes S275–295 and S350–400 in the EC and IC fractions, which may indicate differential release of low and high molecular weight molecules in these two fractions. The opposite occurred with B. licheniformis and P. alvei. The origin of FDOM in HB is an important finding of this work. The most significant amount of protein-like substances was produced at the IC level, with the humic- and fulvic-type at the EC. The main finding of this work is the evidence of differential production of humic-type or protein-type FDOM production by HB species from marine and freshwater aquaculture systems in their intracellular and extracellular fractions, as well different relative molecular weight. For aquaculture, these findings suggest that some bacterial species show promise in supplying essential amino acids to growing organisms, and others play a major role in nutrient exchange and the global carbon cycle.

Characteristics of microplastic pollution and analysis of colonized-microbiota in a freshwater aquaculture system.

The microbial communities associated with microplastics (MPs) and their ambient environments have received wide attention. Although previous studies have reported the differences of microbial communities between MPs and natural environment or substrates, the effects of MPs on microbial balance and functions in ambient water remain unclear, particularly for aquaculture water. Here, we investigated the MPs pollution in farm ponds of grass carp located in the Foshan City of Guangdong Province and reported the distinction of bacterial structures, functions, and complexity between microbiota on MPs and in water. MPs with an average abundance of 288.53 ± 74.27 items/L in pond water were mostly fibers and cellulose, mainly transparent and in size of 0.5–1 mm. Structures and functions of bacterial communities on MPs significantly differed from that in pond water. A large number of enriched or depleted OTUs on MPs compared with water belong to the phylum Proteobacteria, the predominant phylum in microbial communities on MPs and in water. Some species included in the phylum Proteobacteria have been shown to be cellulose-degrading and pathogenic. Microbiota on MPs exhibited higher species richness and diversity as well as a more complex network than that in water, illustrating MPs as a distinct habitat in the aquaculture system.

Effects of ozonation and foam fractionation on rainbow trout condition and physiology in a small-scale freshwater recirculation aquaculture system

The combined use of ozonation and foam fractionation significantly improves the water quality in freshwater recirculating aquaculture systems (RAS). In a recent study, numbers and total volume of suspended particles were reduced by 89% and 76%, respectively, water turbidity was improved by 79% and bacterial activity was reduced by 90% compared to control RAS. In the current study, we assessed the effects of those improvements in water quality on the welfare status of the rainbow trout juveniles present in the RAS. Ozone and foam fractionation were applied separately or in combination in a two-by-two factorial design with triplicated individual RAS. The trial was 8-week long and the welfare of the fish was assessed on week 4 (mid-term) and on week 8 (final). Fish welfare was assessed by using a combination of variables related to physiological stress, oxidative stress, growth performance, energy metabolism and external damage. Feed amounts were kept constant during the study to maintain homogeneous water quality conditions through the study, resulting in a decreasing specific feeding ration during the experiment. Restrictive feeding affected a number of variables related to the metabolic condition of the fish, but those effects were similar for all treatments. Effects of ozonation, foam fractionation and their combination on fish welfare were modest. Both ozone and foam fractionation led to improved skin condition of the fish, and seemed to act complementarily when applied together. Furthermore, foam fractionation had a small significant effect in improving the fish condition factor with respect to the fish in the RAS without foam fractionation. While the size of the described effects was small, they were the result of short-term exposure to the improved water quality. Further studies should focus in investigating the long-term effects of ozonation and foam fractionation on fish welfare in RAS-based aquaculture.

Method for Isolation of Myxozoan Proliferative Stages from Fish at High Yield and Purity: An Essential Prerequisite for In Vitro, In Vivo and Genomics-Based Research Developments.

Myxozoans are a diverse group of microscopic cnidarian parasites and some representatives are associated with important diseases in fish, in both marine and freshwater aquaculture systems. Research on myxozoans has been largely hampered by the inability to isolate myxozoan parasites from their host tissues. In this study, we developed and optimized a method to isolate the myxozoan proliferative stages of different size and cellularity from fish blood, using DEAE-cellulose ion exchange chromatography. We optimized several parameters and obtained 99–100% parasite purity, as well as high survival and infectivity. Using polyclonal pan-carp blood cell-specific antibodies, we further developed a rapid cytometric assay for quantification of the proliferative stages, not only in highly concentrated DEAE-C isolates but also in dilute conditions in full blood. Early developmental stages of myxozoans are key to parasite proliferation, establishment, and pathology in their hosts. The isolation of these stages not only opens new possibilities for in vivo and in vitro studies, but also for obtaining purified DNA and protein extracts for downstream analyses. Hence, we provide a long-desired tool that will advance the functional research into the mechanisms of host exploitation and immune stimulation/evasion in this group, which could contribute greatly to the development of therapeutic strategies against myxozoans.

Characterization of NDM-5-producing Enterobacteriaceae isolates from retail grass carp ( Ctenopharyngodon idella) and evidence of bla NDM-5-bearing IncHI2 plasmid transfer between ducks and fish.

We aimed to characterize NDM-5-producing Enterobacteriaceae from aquatic products in Guangzhou, China. A total of 196 intestinal samples of grass carp collected in 2019 were screened for carbapenemase genes. Characterization of blaNDM-5 positive isolates and plasmids was determined by antimicrobial susceptibility testing, conjugation experiments, Illumina HiSeq, and Nanopore sequencing. One Citrobacter freundii and six Escherichia coli strains recovered from seven intestinal samples were verified as blaNDM-5 carriers (3.57%, 7/196). TheblaNDM-5 genes were located on the IncX3 (n=5), IncHI2 (n=1), or IncHI2-IncF (n=1) plasmids. All blaNDM-5-bearing plasmids were transferred by conjugation at frequencies of ~10−4–10−6. Based on sequence analysis, the IncHI2 plasmid pHNBYF33-1 was similar to other blaNDM-5-carrying IncHI2 plasmids deposited in GenBank from Guangdong ducks. In all IncHI2 plasmids, blaNDM-5 was embedded in a novel transposon, Tn7051 (IS3000-ΔISAba125-IS5-ΔISAba125-blaNDM-5-bleMBL-trpF-tat-∆dct-IS26-∆umuD-∆ISKox3-IS3000), which was identical to the genetic structure surrounding blaNDM-5 found in some IncX3 plasmids. The IncHI2-IncF hybrid plasmid pHNTH9F11-1 was formed by homologous recombination of theblaNDM-5-carrying IncHI2 plasmid and a heavy-metal-resistant IncF plasmid through ∆Tn1721. To the best of our knowledge, this is the first report on the characterization of blaNDM-5-bearing plasmids in fish in China. The IncHI2 plasmid pHNBYF33-1 may be transmitted from ducks, considering the common duck-fish freshwater aquaculture system in Guangdong. Tn7051 is likely responsible for the transfer of blaNDM-5 from IncX3 to IncHI2 plasmids in Enterobacteriaceae, resulting in the expansion of transmission vectors of blaNDM-5.

Potential application of bacteriocins for sustainable aquaculture

AbstractThe emergence and prevalence of bacterial pathogens in freshwater aquaculture systems is a growing concern as the economic losses associated with diseases are mounting and impacting the fishery sector. One way of controlling fish mortality and morbidity is using bacteriocin‐secreting probiotics, which are generally considered safe without any adverse effects that usually accompany other treatment strategies. Understanding the mode of action of bacteriocin on pathogens is vital for considering them suitable for application as a prophylactic in aquaculture. Although several measures such as antibiotic treatment, chemotherapy, vaccination, etc., are available, though not without concerns, these methods have limitations for field‐level applications since they result in several adverse effects both for the animals and the aquatic environment affecting several species in the food chain. In this situation, the use of bacteriocin can be an excellent alternative to minimize the disease burden in freshwater aquaculture if delivered appropriately. Here, we provide an update on the various bacteriocins and their mode of action against important pathogens encountered in aquaculture.

Finfish-Based Bioaugmentation Technology for Enhancing Shrimp Grower’s Income and Livelihood

Penaeid shrimp culture has become an important economic activity in many countries, particularly in Asia. However, environmental challenges and bacterial and viral disease outbreaks are being increasingly recognized as significant constraints on aquaculture production and trade worldwide. Diverse bacterial genera have been associated with infections of penaeid shrimp, but vibriosis is one of the mainly severe bacterial diseases which cause mortality, have been reported in penaeid shrimp culture systems. Tiger shrimp Penaeus monodon and white shrimp Penaeus vannamei are susceptible to fatal effects of luminous vibriosis in India, creating economic losses. There is always a need to control Vibrio harveyi in brackish water shrimp aquaculture. Green water culture system is a biological approach, which integrates the culture of economically important euryhaline finfish as bioaugmentors in the reservoir or net cages/pens in the shrimp growing ponds through zero-water exchange and recirculatory system. The secretions of slime enhance the production of green water which not only suppress the proliferation of luminous bacteria, but also improves the water quality by removing nutrient. In this paper, a hypothesis has been proposed to utilize green water technology as a bioaugmentation technology based on integration of fish green slime beneficial bacteria and their bioactives for controlling priority pathogens in freshwater and brackish water shrimp aquaculture systems for achieving higher shrimp production and enhancing farmers income and livelihood.

Occurrence of Microplastics within a Freshwater Aquaculture System in the Pacific Islands, Viti Levu, Fiji Islands

Occurrence of Microplastics within a Freshwater Aquaculture System in the Pacific Islands, Viti Levu, Fiji Islands

Characters of a nitrobacter enrichment culture from a freshwater aquaculture pond

To isolate nitrite-oxidizing bacteria to control the nitrite concentration in freshwater aquaculture systems, a Nitrobacter enrichment culture was obtained from a freshwater shrimp pond using a continuous enrichment and gradient dilution method. There was only one species of Nitrobacter in the enrichment culture, with an abundance of more than 99%. The Nitrobacter strain was identified as Nitrobacter vulgaris XY-12 on the basis of its 16S rRNA gene and NxrA gene sequences. The effects of pH, temperature, salinity and nitrate on the nitrification activity of the enrichment culture were examined, and its ability to remove nitrite in aquaculture water was also tested. The results showed that the optimum pH for the nitrite-oxidation activity of the enrichment culture was 7.5, the optimum temperature range was 27 °C–30 °C, the optimum salinity was 0.38%, the half maximal inhibitory concentration (IC50) of NO3 −–N was 400 mg L −1, and the optimum concentration of NO2 −–N was 200 mg L −1. In optimum conditions, the maximum NO2 −–N removal rate afforded by the enrichment was 1.62 mg L −1 h −1, and the minimum doubling time was 12 ± 2 h. Moreover, XY-12 could multiply in field aquaculture water, and the maximum NO2 −–N removal rate was 0.15 mg L −1 h −1. These results indicated that the enrichment had good application prospects in aquaculture waters.