Modern Aquaculture Research Articles

СРАВНИТЕЛЬНАЯ ФИЗИОЛОГО-ИММУНОЛОГИЧЕСКАЯ ХАРАКТЕРИСТИКА РЫБ СЕМЕЙСТВА ЦИХЛОВЫЕ И КАРПОВЫЕ

Modern aquaculture is rapidly developing. It includes food fish farming and decorative fish breeding. Like in any fast-growing livestock industry, there may be problems related to the health of fish. Carp is the main object in Russian fish farming, representing the basic type of unpretentious, omnivorous and fast-growing pond polyculture. Tilapia is one of the most preferred species of global aquaculture, due to its hardiness, rapid weight gain and ability to tolerate high planting density. Discus is the most popular of the ornamental fish species; it features a large number of color variations, interesting behavior and is cost-effective in breeding. The authors carried out comparative physiological assessment of bony fish of the cyprinid and cichlid families. Hematological parameters were determined – erythrocyte and leukocyte formulas (by means of differential analysis techniques); biochemical parameters of blood serum (with the analyzer), the average cytochemical coefficient of lysosomal cationic protein content in fish blood neutrophils. The research results showed specific features in the intensity of erythro- and leukopoiesis, the proportion 32 of granular cells of the myeloid series. It was revealed that the peculiarity of discus is the presence of blast forms of white blood cells in the blood: myeloblasts, promyelocytes, and myelocytes. In the blood of tilapia, in contrast to discus and carp, there is a high content of granulocytes: neutrophils, eosinophils and basophils of monocytes and lymphocytes in the leukogram. Differences between species were noted based on the results of the lysosomal cation test. The difference in a number of biochemical parameters can also be seen: in tilapia as compared with other species – in the content of albumins, alkaline phosphatase and ALT, in discus – in the activity of lactate and KK enzymes.

Computer aided design of an aquaculture equipment for the durable development of the marine ecosystem’s biodiversity

Modern aquaculture represents a major innovation in the field of fish production and has been the fastest growing food production sector, reaching an average worldwide growth rate of 6-8% per year. Aquaculture offers important possibilities and generates significant challenges, especially regarding the ecological sustainability of the production, as well as the quality and safety of the products. The epibiont encompass all marine invertebrates that, during the juvenile stages, attach themselves to hard natural supports (rock, submerged rocky platforms) and carry out their entire life cycle [1]. Through the “Strategic guidelines for the sustainable development of aquaculture in the EU”, the European Commission emphasizes the strategic nature of aquaculture production (as well as other productions in the primary sector), so that it can respond to future challenges related to food, natural resources and territories. In order to establish the design parameters of the aquaculture equipment intended for the expansion in space of the group of filtering organisms whose food value and ecological role in maintaining adequate physical, chemical and biological qualities of the seawater are well known, a specialized software was used in order to enable the optimal design and numerical simulation of the conditions in which the equipment operates.

Influence of modern immunobiological preparations based on live bacteria in compound feeds on fish-biological and physiological-biochemical parameters of sturgeon

The efficiency of modern aquaculture largely depends on the properties of the feed used. High-quality compound feed should be used by the body to the maximum extent, stimulate its growth and development, and contribute to the environmental safety of the food products produced. To obtain additional gains in body weight, increase the digestibility and assimilability of feed, stimulate nonspecific immunity and save feed costs, immunobiological preparations based on live bacteria are currently introduced into the composition of feed for animals, including fish. One of the most promising immunobiological preparations based on live bacteria is the probiotic "Ferm-KM" containing phyto-microsorbent particles, live bacillus cells and metabolites: strains Bacillus subtillis, Bacillus licheniformis, complex of lactic acid bacteria and products of their metabolism. The article presents the results of the use of the probiotic "Ferm-KM" in the composition of the production compound feed for sturgeon fish. It was found that when two-year-old Russian sturgeon are grown on a production compound feed with the addition of a probiotic, the fish-breeding and biological parameters of fish increase and the physiological and biochemical parameters of blood improve. The optimal rate of introducing probiotic into the composition of the production compound feed for commercial growing of sturgeon fish is 5 g / kg of compound feed. The effectiveness of introducing a probiotic preparation "Ferm-KM" with an immunomodulatory effect into the composition of compound feed for sturgeon fish has been proved, which helps to increase the linear-weight gain of fish and improve blood parameters.*

Impact of substitution of fish meal by high protein distillers dried grains on growth performance, plasma protein and economic benefit of striped catfish (Pangasianodon hypophthalmus)

Modern aquaculture requires the reduction of the feeds cost, which can partly be achieved by minimal use of dietary animal protein. Therefore, this experiment assessing the nutritional potential of using high protein distillers dried grains (HP-DDG) in formulation of affordable striped catfish, Pangasianodon hypophthalmus, diet for more sustainable development of aquaculture. Four diets containing 0, 25, 50 and 75% HP-DDG as partial replacement of fish meal were fed to P. hypophthalmus (108.58 ± 0.17 g fish−1) reared in circular fibreglass tanks (1 m3 adjusted to 0.8 m3; three replicates treatment−1) at an intial stocking density of 30 fish tank−1. The experiment lasted 14 weeks. The results indicated a significant negative linear regression of growth response (SGR and FCR) with increasing fish meal replacement with HP-DDG according to these formula Y = -0.00444*X + 0.724 and Y = 0.00952*X + 1.583, respectively. The reduction of SGR was 16.44 and 32.88%, and the increasing of FCR was 13.66 and 21.74% by 25 and 50% HP-DDG replacement, respectively compared to the control. The whole-body protein content was significantly decreased and lipids increased with the highest HP-DDG inclusion level. The plasma proteins tended to decrease with increasing HP-DDG (%). Therefore, replacing 25% of fish meal by HP-DDG is acceptable for growth and feed utilization. However, the economic revenue indicated the visibility of replacing 50% of fish meal using HP-DDG as determined by feed cost kg−1 gain (Y = 0.0396*X + 12.84) and net income (Y = -0.2908*X + 47.02).

Development of an enzyme-functionalized immunosensor for measuring maturation-inducing hormone in fish

In modern aquaculture, simple and rapid methods of predicting fish ovulation are needed to produce seedlings in a stable and efficient manner. Ovulation time is variable due to environmental and physiological factors, while 17α,20β-dihydroxy-4-pregnen-3-one (DHP), an indicator of ovulation, increases its concentration rapidly just before spawning. In this paper, we developed a biosensor system in which immune and enzymatic reaction assays were combined to monitor DHP levels with low environmental loads. We attempted to quantify DHP by analyzing the decrease rate in the output current after the immunoreaction using the amperometric method as a transfer inhibition degree of the enzyme-generated electrons generated by the formation of the antigen-antibody complex. DHP standard samples were measured under investigated optimal conditions and a specific response with a good linear correlation was obtained between the current decrease rate of the sensor system and the DHP concentration in a range of 7.81∼500 pg ml−1. Further, DHP levels in goldfish (Carassius auratus) during the ovulation period obtained using the sensor system were compared with those of using the conventional method (ELISA) and a good correlation was obtained. These findings suggest that the proposed sensor system can detect DHP quickly and easily compared with the conventional method.

Assessing effects of dietary supplements on resistance against Yersinia ruckeri infection in rainbow trout (Oncorhynchus mykiss) using different infection models

Ensuring that feed meets the increasing requirements of intense fish production in modern aquaculture is an ongoing process. As antimicrobial growth promotors have been banned from many markets, and as the use of antibiotics represent a rapidly growing concern, disease resistance promoted by functional feed supplements have become increasingly important. The bacterial pathogen Yersinia ruckeri has long been recognized as the cause of enteric redmouth disease. Affecting salmonids, in particular, infection with Y. ruckeri has severe consequences on animal welfare, as well as production economy and prescription of antibiotics.Using recently characterized experimental infection models, we have assessed the effect of prebiotic, probiotic and immunostimulatory feed supplements on resistance towards experimental infection with Y. ruckeri serotype O1 biotype 2 in rainbow trout (Oncorhynchus mykiss). Proprietary, experimental feeds supplemented with organic acid blends, β-glucans either alone or co-supplemented with a nucleotide mix or Pediococcus acidilactici either alone or co-supplemented with mannan oligosaccharides were produced and tested across three separate trials. Using rainbow trout at different weights (3 g, 19 g and 50 g), each trial addressed the effects of these supplements on lysozyme activity and disease resistance following Y. ruckeri infection by cohabitation, intraperitoneal injection or bath exposure. Supplementation with P. acidilactici ± mannan oligosaccharides proved to have a consistent, positive effect on disease resistance. No effects on lysozyme activity was detected for any of the experimental feeds, and only a limited effect on the number of viable Y. ruckeri isolated from the spleen and gut tissues following infection was observed. Finally, the results of this study demonstrate that waterborne infection models causing low to moderate overall mortalities provided better resolution of experimental groups in infection setups testing these feed supplements.

Beneficial bacteria for aquaculture: nutrition, bacteriostasis and immunoregulation.

Despite being the fastest growing sector, the modern aquaculture industry faces serious challenges such as the lack of protein source in feed, the susceptibility to pathogens, and deterioration in quality during culture and storage. Bacterial biomass is considered as a proper protein source for feed, and the beneficial bacterial species protect aquatic animals from infection or reduce spoilage of products. In this review, we summarized the application of beneficial bacteria to aquatic products, focusing mainly on the nutritional, anti-pathogenic, anti-spoilage and immunoregulatory functions of these bacteria. We then discussed the relationship between beneficial bacteria, intestinal microbiota and host immunity, and the recent progress and drawbacks of the technology.

Cell-Based Fish: A Novel Approach to Seafood Production and an Opportunity for Cellular Agriculture

Cellular agriculture is defined as the production of agricultural products from cell cultures rather than from whole plants or animals. With growing interest in cellular agriculture as a means to address the public health, environmental, and animal welfare challenges of animal agriculture, the concept of producing seafood from fish cell- and tissue-cultures is emerging as a means to address similar challenges with industrial aquaculture systems and marine capture. Cell-based seafood - as opposed to animal-based seafood - can combine developments in biomedical engineering with modern aquaculture techniques. Biomedical engineering developments such as closed-system bioreactor production of land animal cells create a basis for large scale production of marine animal cells. Aquaculture techniques such as genetic modification and closed system aquaculture have achieved marked gains in production that can pave the way for innovations in cell-based seafood production. Here, we present the current state of innovation relevant to the development of cell-based seafood across multiple species as well as specific opportunities and challenges that exist for advancing this science. The authors find that the physiological properties of fish cell- and tissue- culture may be uniquely suited to cultivation in vitro. These physiological properties, including hypoxia tolerance, high buffering capacity, and low-temperature growth conditions, make marine cell culture an attractive opportunity for scale production of cell-based seafood; perhaps even more so than mammalian and avian cell cultures for cell-based meats. This, coupled with the unique capabilities of crustacean tissue-friendly scaffolding such as chitosan, a common seafood waste product and mushroom derivative, presents great promise for cell-based seafood production via bioreactor cultivation. To become fully realized, cell-based seafood research will require more understanding of fish muscle culture and cultivation; more investigation into serum-free media formulations optimized for fish cell culture; and bioreactor designs tuned to the needs of fish cells for large scale production.

Spatio-Temporal Pattern of Primary Production in a Tropical Coastal Wetland (Kodungallur-Azhikode Estuary), South West Coast of India

The Kodungallur-Azhikode Estuary (KAE) is part of the Vembanad wetland ecosystem in south-west coast of India that has recently been designated as the Ramsar site. Modern aquaculture, agriculture and other human activities in the catchment area export huge amounts of organic and inorganic wastes into the KAE. In this perspective, influences of anthropogenic activities on water quality and phytoplankton production in the KAE were studied at multiple sites from July 2009 to June 2010. The linear correlation with salinity (r2=0.179, P<0.01), pH (r2=0.195, P<0.01,) and redox potential (Eh) (r2=0.188, P<0.01) was found to be significant with Chlorophyll-a (Chl-a) and negative correlation with turbidity (r2=-0.212, P<0.01, N=168), nitrate (r2=-0.297, P <0.01, N=168), and total dissolved solids (TDS) (r2=-0.266, P<0.01, N=168). The present study showed annual average gross primary productivity (gross PP) of 1580 ± 388 mgC m-3d-1 and net primary productivity (net PP) 790 ± 472 mgC m-3d-1, with significant monthly variation. The mean Chl-a content in the estuary also showed moderately high values (6.42 ± 3.91 mg m-3). In spatial scale, it varied from 5.07 ± 4.03 mg m-3 at Station II to 7.80 ± 6.07 mg m-3 at Station V. Primary productivity in the estuary was nitrogen limited during pre monsoon period, however average N: P ratio in the water column was well above the Redfield ratio during south west monsoon period (27.9 ± 14.2). Trophic Index (TRIX) analysis in the KAE also showed that estuary experiencing high productivity by the effect of eutrophication.

Aquaculture and the displacement of fisheries captures.

In modern aquaculture, animal-production technology is used to increase aquatic food sources. Such controlled rearing of seafood can, in principle, shift the pressure off wild stocks and aquatic ecosystems by reducing fishing activities, which may advance marine conservation goals. We examined resource displacement-the reduced consumption of a resource due to its replacement with a more environmentally benign substitute-in fisheries. We employed panel regression techniques in an analysis of time-series data from 1970 through 2014 to assess the extent to which aquaculture production displaced fisheries captures for all nations for which data were available. We estimated 9 models to assess whether aquaculture production suppresses captures once other factors related to demand have been controlled for. Only 1 model predicted significant suppression of fisheries captures associated with aquaculture systems within nations over time. These results suggest that global aquaculture production does not substantially displace fisheries capture; instead, aquaculture production largely supplements fisheries capture.

Fish response to hypoxia stress: growth, physiological, and immunological biomarkers.

Water quality encompasses the water physical, biological, and chemical parameters. It generally affects the fish growth and welfare. Thus, the success of a commercial aquaculture project depends on supplying the optimum water quality for prompt fish growth at the minimum cost of resources. Although the aquaculture environment is a complicated system, depending on various water quality variables, only less of them have a critical role. One of these vital parameters is dissolved oxygen (DO) level, which requires continuous oversight in aquaculture systems. In addition, the processes of natural stream refinement require suitable DO levels in order to extend for aerobic life forms. The depletion of DO concentration (called hypoxia) in pond water causes great stress on fish where DO levels that remain below 1-2mg/L for a few hours can adversely affect fish growth resulting in fish death. Furthermore, hypoxia has substantial effects on fish physiological and immune responses, making them more susceptible to diseases. Therefore, to avoid disease outbreak in modern aquaculture production systems where fish are intensified and more crowded, increasing attention should be taken into account on DO levels.

ВАКЦИНАЦИЯ В АКВАКУЛЬТУРЕ: ИСТОРИЯ, ЗАКОНОМЕРНОСТИ И ОСОБЕННОСТИ ПРОВЕДЕНИЯ РАБОТ

Historically, different types of fish served as the object of comparative immunology for studying the evolutionary development of immunity. With an increase in the rate of industrial fish rearing, the deterrent role of diseases was established, but at that stage the fight against them was carried out through chemotherapy with antibacterial substances. A special feature of aquaculture is the greater dependence of grown fish on environmental factors that are not influenced as in animal husbandry; therefore, the protection of the organism, based on natural or acquired immunity, is one of the most important components of the health of hydrobionts. In modern aquaculture, disease prevention based on stimulating the immune system – vaccination is an integral part of production management.

Evaluation of the properties of waste from African catfish (Clarias Gariepinus B.) farming in the context of using it for agricultural purposes

Development of modern aquaculture involves increasing the share of production in closed systems with water recirculation. In such facilities, waste with a considerable content of the solid fraction and a high concentration of biogenic elements is generated in the process of water treatment. According to present legislation, such waste cannot be used as fertilizers, which is contradictory to the idea of sustainability and rationalization of the use of environmental resources. The aim of this paper was to assess the chemical composition of African catfish farming waste in the context of the possibility of using it for fertilization purposes. The assumed goal was achieved by studying the waste generated at a water treatment facility that uses the method of active microscreens in an African catfish farm. 10 samples of waste (which, in raw form, is transported to the local wastewater treatment plant) were collected for the research. The content of dry matter, macroelements, microelements and heavy metals was determined in the studied waste. Dry matter content was determined by weight method, nitrogen and carbon content – by elemental analysis method, whereas the content of the other macroelements and trace elements was determined using the ICP-OES method. Results of the conducted research point to high concentrations of nitrogen and phosphorus. These are the main elements which decide on the fertilizing value of the studied material. Nitrogen content was approximately 5.354%, whereas phosphorus content – 3.436% calculated on dry matter. The content of other macroelements and trace elements was at a level observed in natural fertilizers. Heavy metals content did not disqualify the studied material from being used for fertilization purposes. Results of the conducted research indicate unambiguously that the studied material should be used for fertilization. Directing this waste to wastewater treatment plants is not well-founded from the economic and environmental point of view. The issue of proper management of waste generated in aquacultures with water recirculation should be regulated at the legislative level to reduce the amount of biogens dispersed in the environment and to improve the efficiency of production of aquaculture animals.

Male reproductive physiology of Paracentrotus lividus: monthly and seasonal evaluations to study the effects of the environment on gonadal development and sperm cells kinetic

Paracentrotus lividus is a model species for research in different areas, it is also important for modern aquaculture interested in breeding innovative species for greater product diversifications and reduction of the wild stock fishing pressure. This Echinoid was considered a seasonal niche product in the past; nowadays it is highly required on the market for the nutritional characteristics (high protein and low fat) of gonads, the edible part. Our work aims at optimizing farm technics by the study of the habitat impact on P. lividus male reproductive physiology. We correlated environmental variables of the fishing area (temperature, humidity, photoperiod, water temperature, moon phases) to reproductive parameters (morphological gonadal development, sperm cells kinetic). We analyzed data to highlight the relevance, for reproduction, of the length (month or season) of the observations. The significance of this work to the field of aquatic sciences is to drive aquaculture facilities in choosing the desirable period to recover the best spermatozoa with highest total and progressive motility. Moreover setting useful parameters to mimic the best environmental conditions, the highest gonadal development could be reached. This could also promote gametes exchanges between aquaculture facilities in the world taking advantage of the environment dependent gametes maturity.

European sea bass brain DLB-1 cell line is susceptible to nodavirus: A transcriptomic study

Viral diseases are responsible for high rates of mortality and subsequent economic losses in modern aquaculture. The nervous necrosis virus (NNV) produces viral encephalopathy and retinopathy (VER), which affects the fish central nervous system. It is considered one of the most serious viral diseases in marine aquaculture, the European sea bass (Dicentrarchus labrax) being amongst the most susceptible. We have evaluated the European sea bass brain derived cell line (DLB-1) susceptibility to NNV genotypes and evaluated its transcriptomic profile. DLB-1 cells supported NNV gene transcription and replication since strains belonging to the four NNV genotypes produce cytopathic effects. Afterwards, DLB-1 cells were infected with an RGNNV strain, the one which showed the highest replication, for 12 and 72 h and an RNA-seq analysis was performed to identify potential genes involved in the host-NNV interactions. Differential expression analysis showed the up-regulation of many genes related to immunity, heat-shock proteins or apoptosis but not to proteasome or autophagy processes. These data suggest that the immune response, mainly the interferon (IFN) pathway, is not powerful enough to abrogate the infection, and cells finally suffer stress and die by apoptosis liberating infective particles. GO enrichment also revealed, for the first time, the down-regulation of terms related to brain/neuron biology indicating molecular mechanisms causing the pathogenic effect of NNV. This study opens the way to understand key elements in sea bass brain and NNV interactions.

ВЛИЯНИЕ УСЛОВИЙ ВЫРАЩИВАНИЯ НА МОРФО-БИОЛОГИЧЕСКИЕ ОСОБЕННОСТИ СЕГОЛЕТОК СТЕРЛЯДИ (ACIPENSER RUTHENUS (LINNAEUS))

Paper shows research data considering investigation and analysis of specific technological parameters due to external and internal marks of sterlet. Our research goal is to analyze influence of specific sterlet rearing conditions on the morphological, biochemical and hematological marks. Sterlet fry and fingerlings were the object of investigation. Sterlet fingerlings rearing was conducted in experimental ponds (2 ha square) of Dnieprovsky surgeon fish hatching facility. Three variances were formed: І – without fertilizers; ІІ – with organic (3 t/ha) and inorganic fertilizers (50 kg/ha); control – with organic fertilizers (5 t/ha). Stocking density in ponds ranged 95k-100k fishes/ha, stock bodymass ranged from 77,5 to 85,0 mg. Analysis of hydrochemical, morphometric and fishery marks was made according to well-known methods. Water temperature was ranged from 20°С to 27°С, average 24,2–25,4°С. Dissolved oxygen was about 4,6-10,4 mgО 2 /dm 3 . Phytoplankton biomass in I variance ponds ranged from 9,95 to 11,05 g/m 3 , in II variance ponds – 13,6-16,0 g/m 3 . The most abundant zooplankton and zoobenthos was registered in second variance, which was caused by using organic and inorganic fertilizers. Thus, zooplankton biomass was about 8,3–8,6 g/m 3 , zoobenthos –6,69–7,71 g/m 2 . As a result of rearing we received sterlet fingerlings with average individual bodymass 3,2±0,25 g (I variance), 4,17±0,30 g (II variance). The best survival rate (69.55%) and fish productivity (267kg/ha). We can see apparent difference in morphometric if we compare body length (M diff = 3,28-4,08.), pectoventral distance (M diff = 3,10-3,28) and bodymass (M diff = 3,22-3,96). Fulton’s condition factor was ranged from 0,70 in I variance (Cv = 28,21%) to 0,80 in II variance (Cv =27,73%). Analyzing chemical composition of sterlet fingerlings muscle tissue, we defined that moisture was about 80,0–82,2%, lipids – 1,8–2,0%, inorganic – 0,9–1,4%. Protein ranged from 12,6-12,9% (I variance) to 15,0-15,4% (II variance). Overall, biochemical marks of sterlet fingerlings corresponded to physiological standard for this age category. Sterlet fingerling muscle tissue contained less than 0,05% of ammonia, 35,6-50,0 mg/kg of nitrates, 0,6-1,8 mg/kg of nitrites, 190,0-220,0 mg/kg of phosphorus, 0,2-0,22% of NaCl. Acid value for lipids ranged from 0,1 to 0,3 mgКОН. Comparative hematology analysis defined that haemoglobin concentration in different variances ranged from 85 to 159 g/l. Red blood cells concentration was about 0,51-0,93 Т/l, leucocytes - 153-208 g/l, thrombocytes – 25-106 g/l. Relative standard deviation for red blood cells – from 11,8 to 36,4%. Mathematical analysis allowed us to build polynomial equations with coefficient of determination as much as 0,7892–0,9083. Also we investigated influence of rearing conditions in ponds of different fish farms on the separate blood marks. We defined reasonable correlation between level of intensification and main fishery indexes, such as bodymass, fish productivity and survival rate and biochemical marks. Obtained data complement existing technology of sterlet combined rearing in ponds of Southern Ukraine due to its later introduction into natural water reservoirs. Also obtained data may be used in modern aquaculture according to its rearing goals. Keywords: sterlet, fingerling, pond rearing, intensification, fertilizer, survival rate, average individual bodymass, fish productivity, red blood cells, protein, fat.

Carbon: Nitrogen (C:N) ratio level variation influences microbial community of the system and growth as well as immunity of shrimp (Litopenaeus vannamei) in biofloc based culture system

Biofloc technology (BFT) is a novel modern aquaculture farming technique used to reduce toxic nitrogen concentration, act as in situ food source and eradicate pollutants using carbon and therefore to control C:N ratio in an aquaculture system. In this study, effect of different C:N ratios of a biofloc based system on water quality such as the level of Total ammonia nitrogen (TAN) nitrite-nitrogen (NO2−–N) and nitrate nitrogen (NO3−–N) were explored. Further, the growth and immunity status of shrimp L. vannamei under the influence of different C:N ratios were evaluated. Two of the C:N ratios (15 and 20) could significantly (P < 0.05) reduce TAN, NO2-N and NO3-N levels (0.456 ± 0.01, 0.145 ± 0.09, and 0.102 ± 0.02 ppm) compared to control (1.45 ± 0.1, 0.749 ± 0.14 and 0.675 ± 0.16 ppm). Large variations in the frequency distribution of operational taxonomic units (OTUs) for the bacterial community in water with different C:N ration (BFT) and control were observed. Vibrios often considered as opportunistic pathogens, where the most dominant bacterial flora of water in control (79%) and C:N5 (37%) group. In C:N10, Thauera (62%) was most represented genus. Similarly, Attheyaceae (56%), followed by Peridiniaceae (30%) were the most dominant groups in C:N15 treatment. The diversity of bacterial flora was more spread in C:N20 treatments with Psychrobacter (26%), Proteobacteria (25%) and Peridiniaceae (20%) as the major groups. The trend of Vibrio dominance decreased with the increase in C:N ratios and thus confirming the dominance of heterotrophic bacteria in high C:N ratio groups. Upon challenge with pathogens, shrimps from C:N10, C:N15 and C:N20 groups showed significantly higher survival (P < 0.05) compared to the C:N5 and control group. Similarly, better growth rate was also observed in BFT tanks compared to control both during the culture and at harvest. Comparatively higher expression of four immune-related genes (ras-related nuclear gene (RAN), serine proteinase gene (SP), prophenoloxidase activating enzyme (PPAE), and crustin were observed in different C:N ratio ponds than control and these were in increasing trend with the C:N ratio. Gene expression analysis showed that the transcripts of those immune genes were significantly increased among all C:N treatments than that of control. Overall, these findings demonstrated that with optimum C:N ratio, BFT can be used to optimize the bacterial community composition for both optimal water quality and optimal shrimp health. This study thus indicates the possibility of obtaining better performance of L. vannamei culture with proper adjustment of C:N ratio in a biofloc based system.

New insights on the macromolecular building of rainbow trout (O. mykiss) intestine: FTIR Imaging and histological correlative study

Fish intestine plays various physiological functions and its integrity is essential to guarantee fish growth and welfare. Several laboratory techniques have been proposed for studying morpho-physiology of fish intestine, but classical histology still represents one of the gold standards. Nevertheless, this technique is time consuming and does not provide comprehensive information on the biochemical composition of tissues. The present study, introduces a new approach for studying fish intestine, the Fourier Transform Infrared (FTIR) spectroscopy. This is a fast, label-free analytical technique, which analyses the vibrational transitions induced on tissues by the interaction with the electromagnetic radiation. On the base of vibrational features of some functional groups classes and molecular bonds, FTIR allows the analysis of the macromolecular composition of the sample. Rainbow trout (O. mykiss) represents an important species for modern aquaculture and deeper knowledge about its intestine anatomy and macromolecular composition is desirable. In the present study, besides the traditional histological analysis, the biochemical building of the intestine mucosa was analyzed for the first time by FTIR. Spectral data can be considered a complement to traditional histological analysis.

Recombinant infectious hematopoietic necrosis virus expressing infectious pancreatic necrosis virus VP2 protein induces immunity against both pathogens

Infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) are typical pathogens of rainbow trout. Their co-infection is also common, which causes great economic loss in juvenile salmon species. Although vaccines against IHNV and IPNV have been commercialized in many countries, the prevalence of IHNV and IPNV is still widespread in modern aquaculture. In the present study, two IHNV recombinant viruses displaying IPNV VP2 protein (rIHNV-IPNV VP2 and rIHNV-IPNV VP2COE) were generated using the RNA polymerase Ⅱ system to explore the immunogenicity of IHNV and IPNV. The recombinant IHNV viruses were stable, which was confirmed by sequencing, indirect immunofluorescence assay, western blotting, transmission electron microscopy and viral growth curve assay. IHNV and IPNV challenge showed that the recombinant viruses had high protection rates against IHNV and IPNV with approximately 65% relative percent survival rates. Rainbow trout (mean weight 20 g) vaccinated with these two recombinant viruses showed a high level of antibodies against IHNV and IPNV infection. Taken together, our findings demonstrate that rIHNV-IPNV VP2 and rIHNV-IPNV VP2COE might be promising vaccine candidates against IHNV and IPNV.

Genes related to cell-mediated cytotoxicity and interferon response are induced in the retina of European sea bass upon intravitreal infection with nodavirus

Viral diseases are responsible for high rates of mortality and subsequent economic losses in modern aquaculture. The nervous necrosis virus (NNV) produces viral encephalopathy and retinopathy (VER), which affects the central nervous system, is considered one of the most serious viral diseases in marine aquaculture. Although some studies have localized NNV in the retina cells, none has dealt with immunity in the retina. Thus, for the first time, we intravitreally infected healthy specimens of European sea bass (Dicentrarchus labrax) with NNV with the aim of characterizing the immune response in the retina. Ultrastructural analysis detected important retinal injuries and structure degradation, including pycnosis, hydropic degeneration and vacuolization in some cell layers as well as myelin sheaths in the optic nerve fibres. Immunohistochemistry demonstrated that NNV replicated in the eyes. Regarding retinal immunity, NNV infection elicited the transcription of genes encoding proteins involved in the interferon (IFN) and cell-mediated cytotoxicity (CMC) responses as well as B and T cell markers, demonstrating that viral replication influences innate and adaptive responses. Further studies are needed to understand the retina immunity and whether the main retinal function, vision, is affected by nodavirus.