Enhanced efficacy of immersion vaccination in tilapia against columnaris disease by chitosan-coated "pathogen-like" mucoadhesive nanovaccines

Evaluation of immune responses and protection in Asian seabass (Lates calcarifer Bloch, 1790) against Vibrio vulnificus using immersion and oral nanoemulsion vaccines

Vaccination is an important strategy in aquaculture for enhancing disease resistance and ensuring the health and productivity of cultured fish. This study investigated the distinct systemic and mucosal immune responses elicited by immersion (ImV) and oral (OrV) nanoemulsion vaccines encapsulating Vibrio vulnificus in Asian seabass (Lates calcarifer). Two vaccination methods, ImV and OrV, were administered to separate groups of Asian seabass, followed by challenges with V. vulnificus via immersion and intraperitoneal (i.p.) injection administration. Immune responses were assessed by measuring specific IgM antibodies, lysozyme activity, bactericidal activity, and immune-related gene expression across multiple organs, including serum, head kidney, liver, gills, skin, and intestine. The results demonstrate that the OrV group had a significantly increased level of specific IgM antibody in their serum, head kidney and liver compared to the immersion vaccine group and control, with the OrV group maintaining higher antibody levels post-immersion and injection challenge. In mucosal tissues, the ImV group elicited stronger IgM responses in the gills and skin, whereas the OrV group enhanced antibody responses in the liver and intestine. Lysozyme and bactericidal activities varied by organ and vaccination route, indicating differential activation of innate immune defenses. Additionally, immune-related gene expression was upregulated in a tissue-specific manner, reflecting the targeted activation of adaptive and innate immune mechanisms by each vaccine type. Both vaccination strategies significantly improved survival and relative percent survival (RPS), with ImV offering stronger protection against immersion challenges, while OrV provided strong protection in systemic (injection) challenges. These findings suggest that ImV and OrV groups induced distinct immune responses in Asian seabass, with immersion vaccination primarily enhancing mucosal immunity at barrier surfaces and oral vaccination promoting systemic and intestinal mucosal immunity. The integration of both vaccination strategies could provide synergistic protection, enhancing vaccine efficacy against V. vulnificus and other pathogens, thereby optimizing disease prevention and fish health management in aquaculture settings.

Effectiveness of a new cationic lipid-based nanovaccine for enhancing immersion vaccination against Flavobacterium oreochromis in red tilapia (Oreochromis sp.)

Flavobacterium oreochromis (Fo) poses a significant threat to tilapia, leading to economic losses due to mortality. Immersion vaccines, while practical for small fish, often result in limited antigen absorption. This study aimed to develop a cationic lipid-based nanoparticle vaccine using cetyltrimethylammonium bromide (CTAB) and evaluate its efficacy against F. oreochromis in red tilapia. In the first trial, healthy red tilapia were immersion vaccinated for 30 min, with three groups included in the trial: control (non-vaccinated), formalin-killed sonicated cells (FK-SC), or cationic lipid-based nanoparticles (Fo-NV). The second trial followed the same design, with booster vaccinations (FK-SC-B, Fo-NV-B) administered 14 days after the first vaccination. Fish were challenged with virulent F. oreochromis at multiple time points up to 120 days post-vaccination (dpv) in the first trial and up to 180 dpv in the second, with survival recorded for 10 days post-challenge during each challenge. Specific IgM antibody levels were measured at various dpv intervals. The Fo-NV group, characterized by nanoscale size (179 nm) and positive charge (13 mV), showed enhanced stability and mucoadhesion compared to FK-SC. In the first trial, the Fo-NV group had significantly higher relative percentage survival (RPS) (83.3-63.3 %) compared to FK-SC (33.3-10.0 %) during the first three months. In the second trial, the Fo-NV-B group exhibited elevated IgM levels and higher RPS (81.8-58.5 %) compared to control groups over five months. In conclusion, a booster dose of Fo-NV improved vaccine efficacy, enhancing antigen delivery to mucosal surfaces and providing prolonged protection against F. oreochromis infection.

Advances in Vaccine Adjuvants for Teleost Fish: Implications for Aquatic Welfare and the Potential of Nanoparticle-Based Formulations

Vaccine adjuvants are crucial for reinforcing the immunogenicity of vaccines. Therefore, they are widely used in the aquaculture sector as vaccine components, facilitating the efficient prevention of infectious diseases and promoting sustainable teleost fish growth. Despite their benefits, there has been a growing concern about the potential adverse effects of vaccine adjuvants in teleost fish, connoting a valid impact on their overall health and welfare. Among the adjuvants used in aquaculture vaccinology, nanoparticle-based formulations have given rise to a promising new alternative to traditional options, such as oil-based emulsions and aluminum compounds, offering the benefit of minimizing relevant side effects. The aim of this paper was to review the current status of the adjuvants used in aquaculture, provide a description and an evaluation of their mode of action and side effects, and explore the potential use of nanoparticle formulations as adjuvants to improve the efficacy of aquaculture vaccines. By demonstrating and assessing the equilibrium between teleost fish welfare and immunological efficacy, this review presents a collective perspective that will assist in establishing a framework for the utilization of effective species-specific practices around adjuvant use in aquaculture, while also addressing the challenges of welfare-friendly immunization.

Chitosan non-particulate vaccine delivery systems

Chitosan is an extensively used polymer for drug delivery applications in particulate and non-particulate carriers. Chitosan-based particulate, nano-, and microparticle, carriers have been the most extensively studied for the delivery of therapeutics and vaccines. However, chitosan has also been used in vaccine applications for its adjuvant properties in various hydrogels or as a carrier coating material. The focus of this review will be on the usage of chitosan as a vaccine adjuvant based on its intrinsic immunogenicity; the various forms of chitosan-based non-particulate delivery systems such as thermosensitive hydrogels, microneedles, and conjugates; and the advantages of its role as a coating material for vaccine carriers.

A novel vaccination strategy against Vibrio harveyi infection in Asian seabass (Lates calcarifer) with the aid of oxygen nanobubbles and chitosan

Immersion vaccination, albeit easier to administer than immunization by injection, sometimes has challenges with antigen uptake, resulting in sub-optimal protection. In this research, a new strategy to enhance antigen uptake of a heat-inactivated Vibrio harveyi vaccine in Asian seabass (Lates calcarifer) using oxygen nanobubble-enriched water (ONB) and positively charged chitosan (CS) was explored. Antigen uptake in fish gills was assessed, as was the antibody response and vaccine efficacy of four different combinations of vaccine with ONB and CS, and two control groups. Pre-mixing of ONB and CS before introducing the vaccine, referred to as (ONB + CS) + Vac, resulted in superior antigen uptake and anti-V. harveyi antibody (IgM) production in both serum and mucus compared to other formulas. The integration of an oral booster (4.22 × 108 CFU/g, at day 21-25) within a vaccine trial experiment set out to further evaluate how survival rates post exposure to V. harveyi might be improved. Antibody responses were measured over 42 days, and vaccine efficacy was assessed through an experimental challenge with V. harveyi. The expression of immune-related genes IL1β, TNFα, CD4, CD8, IgT and antibody levels were assessed at 1, 3, and 7-day(s) post challenge (dpc). The results revealed that antibody levels in the group (ONB + CS) + Vac were consistently higher than the other groups post immersion immunization and oral booster, along with elevated expression of immune-related genes after challenge with V. harveyi. Ultimately, this group demonstrated a significantly higher relative percent survival (RPS) of 63 % ± 10.5 %, showcasing the potential of the ONB-CS-Vac complex as a promising immersion vaccination strategy for enhancing antigen uptake, stimulating immunological responses, and improving survival of Asian seabass against vibriosis.

Systemic and mucosal immune responses in red tilapia (Oreochromis sp.) following immersion vaccination with a chitosan polymer-based nanovaccine against Aeromonas veronii

A mucoadhesive chitosan polymer-based nanoplatform has been increasingly recognized as an effective mucosal vaccine delivery system for fish. The present study aimed to investigate the effectiveness of immersion vaccination with a chitosan polymer-based nanovaccine to elicit an immune response in serum and mucus of red tilapia and evaluate its protective efficacy after immersion challenge with a heterogenous strain of Aeromonas veronii UDRT09. Six hundred red tilapia (22 ± 1.8 g) were randomly allocated into four experimental groups: control, empty-polymeric nanoparticle (PC), formalin-killed vaccine (FKV), and chitosan polymer-based nanovaccine (CS-NV) in triplicate. The specific IgM antibody levels and their bactericidal activity were assessed in serum and mucus for 28 days after immersion vaccination and followed by immersion challenge with A. veronii. The immersion vaccine was found to be safe for red tilapia, with no mortalities occurring during the vaccination procedure. The specific IgM antibody levels and bactericidal activity against A. veronii in both serum and mucus were significantly higher in red tilapia vaccinated with CS-NV compared to the FKV and control groups at all time points. Furthermore, the serum lysozyme activity, ACH50, and total Ig levels demonstrated a significant elevation in the groups vaccinated with CS-NV compared to the FKV and control groups. Importantly, the Relative Percentage Survival (RPS) value of the CS-NV group (71 %) was significantly higher than that of the FKV (15.12 %) and PC (2.33 %) groups, respectively. This indicates that the chitosan polymer-based nanovaccine platform is an effective delivery system for the immersion vaccination of tilapia.

Development of Immersion and Oral Bivalent Nanovaccines for Streptococcosis and Columnaris Disease Prevention in Fry and Fingerling Asian Seabass (Lates calcarifer) Nursery Farms

In the present study, chitosan-based bivalent nanovaccines of S. iniae and F. covae were administered by immersion vaccination at 30 and 40 days after hatching (DAH), and the third vaccination was orally administered by feeding at 50 DAH. ELISA revealed that the levels of total IgM and specific IgM to S. iniae and F. covae were significantly elevated in all vaccinated groups at 10, 20, and 30 days after vaccination (DAV). A qRT-PCR analysis of immune-related genes revealed significantly higher IgT expression in the vaccinated groups compared to the control group, as revealed by 44-100-fold changes in the vaccinated groups compared to the control (p < 0.001) at every tested time point after vaccination. All vaccinated groups expressed IgM, MHCIIα, and TCRα at significantly higher levels than the control group at 10 and/or 20 DAV (p < 0.05). In the S. iniae challenge tests, the survival of vaccinated groups ranged from 62.15 ± 2.11 to 75.70 ± 3.36%, which significantly differed from that of the control group (44.44 ± 1.92%). Similarly, all vaccinated groups showed higher survival rates of 68.89 ± 3.85 to 77.78 ± 5.09% during F. covae challenge than the control groups (50.00 ± 3.33%) (p < 0.05).

Addressing Nanovaccine Strategies for Tilapia

Tilapia is the world's most extensively farmed species after carp. It is an attractive species for aquaculture as it grows quickly, reaching harvest size within six to seven months of production, and provides an important source of food and revenue for many low-income families, especially in low- to middle-income countries. The expansion of tilapia aquaculture has resulted in an intensification of farming systems, and this has been associated with increased disease outbreaks caused by various pathogens, mostly bacterial and viral agents. Vaccination is routinely used to control disease in higher-value finfish species, such as Atlantic salmon. At the same time, many tilapia farmers are often unwilling to vaccinate their fish by injection once the fish have been moved to their grow-out site. Alternative vaccination strategies are needed to help tilapia farmers accept and use vaccines. There is increasing interest in nanoparticle-based vaccines as alternative methods for delivering vaccines to fish, especially for oral and immersion administration. They can potentially improve vaccine efficacy through the controlled release of antigens, protecting antigens from premature proteolytic degradation in the gastric tract, and facilitating antigen uptake and processing by antigen-presenting cells. They can also allow targeted delivery of the vaccine at mucosal sites. This review provides a brief overview of the bacterial and viral diseases affecting tilapia aquaculture and vaccine strategies for farmed tilapia. It focuses on the use of nanovaccines to improve the acceptance and uptake of vaccines by tilapia farmers.

Oral delivery of a Streptococcus agalactiae vaccine to Nile tilapia (Oreochromis niloticus) using a novel cationic-based nanoemulsion containing bile salts

Streptococcus agalactiae is one of Thailand's most important pathogens in tilapia aquaculture. Vaccination is a very effective method for protecting fish against disease in aquaculture. Oral vaccination is an interesting route for vaccine delivery as it mimics the pathogenesis of S. agalactiae and provides convenient administration for mass vaccination of fish. Moreover, gut mucosal immunity is associated with a mucus layer on the gastrointestinal tract. Therefore, this study aimed to develop a novel cationic-based nanoemulsion vaccine containing bile salts (NEB) coated by chitosan (CS) and determined its physicochemical characterization, morphology, in vitro mucoadhesive property, permeability, and acid-base tolerance. In addition, the efficacy of NEB-CS as an oral vaccination for Nile tilapia was evaluated in order to investigate the innate immune response and protection against S. agalactiae. The groups of fish consisted of: (1) deionized water as a non-vaccinated control (Control); (2) an inactivated vaccine formulated from formalin-killed bacteria (IB); and (3) a novel cationic-based nanoemulsion vaccine containing bile salts (NEB) coated by chitosan (CS). The control, IB, and NEB-CS were incorporated into commercial feed pellets and fed to Nile tilapia. In addition, we evaluated the serum bactericidal activity (SBA) for 14 days post-vaccination (dpv) and protective efficacy for 10 days post-challenge, respectively. The mucoadhesiveness, permeability, and absorption within the tilapia intestine were also assessed in vivo. The NEB-CS vaccine appeared spherical, with the nanoparticles having a size of 454.37 nm and a positive charge (+47.6 mV). The NEB-CS vaccine had higher levels of mucoadhesiveness and permeability than the NEB (p < 0.05). The relative percentage survival (RPS) of IB and NEB-CS, when administered orally to fish, was 48% and 96%, respectively. Enhanced SBA was noted in the NEB-CS and IB vaccine groups compared to the control group. The results demonstrate that a feed-based NEB-CS can improve the mucoadhesiveness, permeability, and protective efficacy of the vaccine, and appear to be a promising approach to protecting tilapia in aquaculture against streptococcosis.

Chitosan nanoparticle immersion vaccine offers protection against tilapia lake virus in laboratory and field studies

Tilapia lake virus (TiLV), an enveloped negative-sense single-stranded RNA virus, causes tilapia lake virus disease (TiLVD), which is associated with mass mortality and severe economic impacts in wild and farmed tilapia industries worldwide. In this study, we developed a chitosan nanoparticle TiLV immersion vaccine and assessed the efficacy of the vaccine in laboratory and field trials. Transmission electron microscopy showed that the inactivated vaccine had a particle size of 210.3 nm, while the nano inactivated vaccine had a spherical shape with a diameter of 120.4 nm. Further analysis using fluorescent staining and immunohistochemistry analysis revealed the mucoadhesive properties of the nanovaccine (CN-KV) through fish gills. We assessed the efficacy of an immersion-based TiLV nanovaccine using a cohabitation challenge model. The fish that received the nanovaccine showed better relative percent survival (RPS) at 68.17% compared with the RPS of the inactivated virus vaccine (KV) group at 25.01%. The CN-KV group also showed a higher TiLV-specific antibody response than the control and KV groups (p < 0.05). Importantly, under field conditions, the fish receiving the CN-KV nanovaccine had better RPS at 52.2% than the nonvaccinated control group. Taken together, the CN-KV nanovaccinated fish showed better survival and antibody response than the control and KV groups both under laboratory control challenge conditions and field trials. The newly developed immersion-based nanovaccine is easy to administer in small fish, is less labor-intensive, and allows for mass vaccination to protect fish from TiLV infection.

Chitosan-nanoparticles effects on mucosal immunity: A systematic review

Nanoparticles-based treatments is of utmost importance for aquaculture. In this scenario, chitosan-based nanoparticles have been proposed due to the properties of chitosan, which include mucoadhesiveness. Nevertheless, pivotal parameters of chitosan, such as degree of acetylation and molecular weight, are commonly underestimated in the available literature despite the influence they seem to have on the properties of chitosan-based nanoparticles. In this systematic review, the immunomodulator capacity of chitosan nanoparticles used as mucosal vaccines on teleost fish has been evaluated paying special attention to the chitosan properties. Four databases were used for literature search, yielding 486 documents, from which 14 meet the inclusion criteria. Only 21% of the available studies reported properly chitosan properties, which should be improved in future works to generate reproducible data as well as valuable information. To the best of our knowledge, this work objectively compares for the first time, by quantifying the mg of chitosan/g of fish applied in each study, the chitosan nanoparticle preparation and doses applied to fish, as well as the effects of the treatments applied on fish immune status.

Chitosan-polymer based nanovaccine as promising immersion vaccine against Aeromonas veronii challenge in red tilapia (Oreochromis sp.)

Red tilapia (Oreochromis sp.), one of the important freshwater fish species in fish farming in Thailand, has for long been suffering from a serious bacterial disease named epizootic ulcerative syndrome and hemorrhagic septicemia. The disease is mainly caused by Aeromonas veronii. Vaccine is proposed to be a major impact tool for sustainable control and prevention strategies. Vaccination by immersion has many benefits over injection. However, the conventional immersion method suffers from a low potency due to the inefficient uptake of antigens across mucosal tissue. Here, we developed a chitosan-polymer based nanovaccine together with an efficient delivery vehicle to enhance the immunogenicity of immersion vaccination, increasing bioavailability and inducing local immune responses during transit to mucosal inductive immune sites. The physiochemical properties of nanovaccine, which was modified on surface particle by using a mucoadhesive polymer, were assessed for size, zeta potential, and particle distribution. Our study demonstrated by SEM image and microscopic fluorescence image that nanovaccine greatly increased the binding and penetrating ability into gills when compared with formalin killed vaccine. The nano-sized particles were well dispersed in water and trapped in core nanoparticle as confirmed by TEM image. The efficacy of vaccine was performed by immersion challenge with virulent A.veronii after 30 days post vaccination in tilapia. The result revealed a high level of mortality in the control, empty-polymeric nanovaccine and formalin killed bacterin vaccine groups. A high relative percentage survival (RPS) of vaccinated fish was noted with chitosan-polymer based nanovaccine. Our studies indicated that this chitosan-polymer based nanovaccine derived from cell fragments and supernatant was the improved version of the conventional formalin killed vaccine. The chitosan polymer based particle could increase the efficacy of nanovaccine toward the target mucosal membrane and enhance protection against A. veronii infection in red tilapia.

Novel development of cationic surfactant-based mucoadhesive nanovaccine for direct immersion vaccination against Francisella noatunensis subsp. orientalis in red tilapia (Oreochromis sp.)

Francisella noatunensis subsp. orientalis (Fno) is one of the infectious diseases that causes economic losses associated with tilapia mortality. Even though direct immersion administration of vaccines is more practicable for small fish and fry compared with oral and injection vaccination in the fields, the efficacy is still insufficient due to lower potency of antigen uptake. Herein, we accomplished the development of a mucoadhesive nanovaccine platform using cetyltrimethylammonium bromide (CTAB), a cationic surfactant, to improve the efficiency of immersion vaccination against Fno in tilapia. Cationic Fno nanovaccine (CAT-Fno-NV) was prepared though emulsification using an ultrasonic method. In our investigation, the CAT-Fno-NV increased the opportunity of Fno vaccine uptake by extending the contact time between vaccine and mucosal surface of fish gills and enhancing the protective efficacy against Fno infection. Fish were vaccinated with the CAT-Fno-NV by a direct immersion protocol. The challenge trial by Fno injection revealed that CAT-Fno-NV at the concentration 1:100 ratio (approximately 1 × 10⁶ cfu/mL) had the highest efficacy to protect fish from Fno infection at day 30 after post challenge period according to the total number of Fno detected in head kidney, spleen and liver. A significant upregulation of IgM gene was observed in gills, skin, head kidney, serum and peripheral blood lymphocytes (PBLs) and spleen tissues treated with WC and CAT-Fno-NV (1:100) vaccines, while IgT gene was highly expressed in only gills and skin tissues for treated WC and CAT-Fno-NV (1:100) groups. We anticipate that the cationic surfactant-based nanovaccine developed in this study could become an efficient alternative for direct immersion vaccination to induce humoral immune responses against Fno in vaccinated tilapia.

Challenges in Veterinary Vaccine Development

Animals provide food and clothing in addition to other value-added products. Changes in diet and lifestyle have increased the consumption and the use of animal products. Infectious diseases in animals are a major threat to global animal health and its welfare; their effective control is crucial for agronomic health, for safeguarding food security and also alleviating rural poverty. Development of vaccines has led to increased production of healthy poultry, livestock, and fish. Animal production increases have alleviated food insecurity. In addition, development of effective vaccines has led to healthier companion animals. However, challenges remain including climate change that has led to enhancement in vectors and pathogens that may lead to emergent diseases in animals. Preventing transmission of emerging infectious diseases at the animal-human interface is critically important for protecting the world population from epizootics and pandemics. Hence, there is a need to develop new vaccines to prevent diseases in animals. This review describes the broad challenges to be considered in the development of vaccines for animals.

Immersion Vaccination by a Biomimetic-Mucoadhesive Nanovaccine Induces Humoral Immune Response of Red Tilapia (Oreochromis sp.) against Flavobacterium columnare Challenge

Immersion vaccination with a biomimetic mucoadhesive nanovaccine has been shown to induce a strong mucosal immune response against columnaris disease, a serious bacterial disease in farmed red tilapia caused by Flavobacterium columnare. However, the induction of a systemic immune response by the vaccine is yet to be investigated. Here, we examine if a specific humoral immune response is stimulated in tilapia by a biomimetic-mucoadhesive nanovaccine against Flavobacterium columnare using an indirect-enzyme-linked immunosorbent assay (ELISA), serum bactericidal activity (SBA) and the expression of immune-related genes within the head-kidney and spleen, together with assessing the relative percent survival of vaccinated fish after experimentally infecting them with F. columnare. The anti-IgM antibody titer of fish at 14 and 21 days post-vaccination was significantly higher in chitosan complex nanoemulsion (CS-NE) vaccinated fish compared to fish vaccinated with the formalin-killed vaccine or control fish, supporting the serum bactericidal activity results at these time points. The cumulative mortality of the unvaccinated control fish was 87% after challenging fish with the pathogen, while the cumulative mortality of the CS-NE vaccinated group was 24%, which was significantly lower than the formalin-killed vaccinated and control fish. There was a significant upregulation of IgM, IgT, TNF α, and IL1-β genes in the spleen and kidney of vaccinated fish. Significant upregulation of IgM and IgT genes was observed in the spleen of CS-NE vaccinated fish. The study confirmed the charged-chitosan-based mucoadhesive nanovaccine to be an effective platform for immersion vaccination of tilapia, with fish generating a humoral systemic immune response against columnaris disease in vaccinated fish.

Protective Efficacy of Novel Oral Biofilm Vaccines against Lactococcus garvieae Infection in Mullet, Mugil cephalus

Lactococcus garvieae (L. garvieae) is an important pathogen that causes enormous economic losses in both marine and freshwater aquaculture. At present, antibiotics are the only option for farmers to reduce the losses caused by L. garvieae. However, the usage of antibiotics leads to environmental pollution and the production of drug-resistant strains of bacteria. Therefore, vaccination is preferred as an alternative method to prevent infectious diseases. In this study, we describe an effective approach to the production of an oral biofilm vaccine, using bacteria grown on chitosan particles to form biofilms, and thus providing an inactive pathogen that enhances the immune response in fish. We observed the formation of a biofilm on chitosan particles and administered the novel oral biofilm vaccine to fish. We analyzed the immune responses, including antibody production, phagocytic ability, albumin/globulin ratio and immune-related genes, of vaccinated and control groups of black mullet. Our results show that the phagocytic ability of the biofilm vaccine group was 84%, which is significantly higher than that of the control group, and the antibody production in this group was significantly higher compared with the other group. The mRNA expression levels of immune-related genes (TLR2, IL-1β, TNF-α) were significantly upregulated in the spleen after vaccination. In challenge experiments, the relative percent survival (RPS) was 77% in the biofilm vaccine group, 18% in the whole-cell vaccine group, and 0% in the chitosan particle group at 32 days post-vaccination. In addition, we also found that the relative percent survival (RPS) at 1 day post-vaccination was 74% in the biofilm vaccine group, 42% in the whole-cell vaccine group, and 26% in the chitosan particle group. In both long-term and short-term challenge experiments, the viability of the biofilm vaccine group was significantly higher than that of the whole-cell, chitosan particle and PBS groups. We conclude that based on its protective effect, the L. garvieae biofilm vaccine is better than the whole-cell vaccine when challenged several weeks after vaccination. In addition, the biofilm vaccine also has a greater protective effect than the whole-cell vaccine when challenged immediately after vaccination. Therefore, the biofilm vaccine might represent a novel method for the prevention and treatment of L. garvieae infection.

Modulation of the mucosal immune response of red tilapia (Oreochromis sp.) against columnaris disease using a biomimetic-mucoadhesive nanovaccine

Columnaris, a highly contagious bacterial disease caused by Flavobacterium columnare, is recognized as one of the most important infectious diseases in farmed tilapia, especially during the fry and fingerling stages of production. The disease is associated with characteristic lesions in the mucosa of affected fish, particularly their skin and gills. Vaccines delivered via the mucosa are therefore of great interest to scientists developing vaccines for this disease. In the present study, we characterized field isolates of F. columnare obtained from clinical columnaris outbreaks in red tilapia to select an isolate to use as a candidate for our vaccine study. This included characterizing its colony morphology, genotype and virulence status. The isolate was incorporated into a mucoadhesive polymer chitosan-complexed nanovaccine (CS-NE), the efficacy of which was determined by experimentally infecting red tilapia that had been vaccinated with the nanoparticles by immersion. The experimental infection was performed 30-days post-vaccination (dpv), which resulted in 89% of the unvaccinated control fish dying, while the relative percentage survival (RPS) of the CS-NE vaccinated group was 78%. Histology of the mucosal associated lymphoid tissue (MALT) showed a significantly higher presence of leucocytes and a greater antigen uptake by the mucosal epithelium in CS-NE vaccinated fish compared to control fish and whole cell vaccinated fish, respectively, and there was statistically significant up-regulation of IgT, IgM, TNF α, IL1-β and MHC-1 genes in the gill of the CS-NE vaccinated group. Overall, the results of our study confirmed that the CS-NE particles achieved better adsorption onto the mucosal surfaces of the fish, elicited great vaccine efficacy and modulated the MALT immune response better than the conventional whole cell-killed vaccine, demonstrating the feasibility of the mucoadhesive nano-immersion vaccine as an effective delivery system for the induction of a mucosal immune response against columnaris disease in tilapia.

Advantages and prospective challenges of nanotechnology applications in fish cultures: a comparative review

Applications of nanotechnology in fish cultures have participated in getting over various difficulties that hinder fish productivity. They can achieve growth performance after adding some important minerals and vitamins in the form of nano-feed supplements like selenium, zinc, iron, and vitamin C. Also, they have an important role in reproduction, and fish medicine as antimicrobial, drug delivery, nano-vaccination, and rapid disease diagnosis. Moreover, their roles in water remediation and purification, and fish packaging are documented. On the other hand, some nanoparticles exhibit toxic effects on living organisms, which return to their tiny size, high reactivity, and permeability. They can alter many physiological functions and cause cytotoxicity, DNA damage, and histopathological changes. Also, nanotechnology applications cause new secondary pollutants to be introduced into the environment that can negatively affect fish health and the surrounding living organisms. So, in spite of the promising applications of nanotechnology to fulfill high growth performance and pathogen-free fish, there are a lot of debates about the potential toxicity of nanomaterials, their reactivity with the surrounding environment, and bioaccumulation. The present review aims to elucidate and discuss various advantages and challenges of nanotechnology applications in fish cultures. Also, it points to green nanotechnology as a promising alternative to chemical ones.

Analysis of the treatment regimen efficacy for columnaris disease in Pterophyllum scalare

The article presents the results of studies on the treatment scheme efficacy for columnaris in Pterophyllum scalare, common under private aquarium husbandry conditions. To establish the diagnosis, the clinical features of the diseased fish, pathological and anatomical changes and the results of microscopic and microbiological studies were taken into account. Separate chemical and microbiological parameters of aquarium water were also studied. It was established that fish disease developed against the background of adverse changes in the chemical composition and microbiocenosis of aquarium water. High alkalinity and excess of phosphates compared to the norm provoked accumulation of opportunistic microbiota, resulting in a balance disorder in the parasite-host system and development of clinical manifestation of the fish disease. During the disease outbreak, bacteriological indices of water indicated a high level of organic contamination and a low intensity of water self-purification processes. Clinically, the disease was manifested in P. scalare by decrease in appetite and motor activity, onset of ulcerative lesions of various shapes and sizes on the surface of the body and on the gill covers. Selected pure cultures of Flavobacterium columnare showed sensitivity to enrofloxacin (growth retardation zone 31.3 ± 1.0 mm); moderate resistance was found to tylosin. The microorganisms were resistant to amoxicillin, doxycycline, benzylpenicillin and tetracycline. Microscopic studies of intestinal specimens of dead P. scalare revealed numerous motile flagellates. It has been shown that an effective treatment regimen that provides recovery for 70% of diseased P. scalare is the use of enroxil 10% solution for five days, metronidazole three times a day, and “API MelaFix” for seven days. It is proved that the following measures are effective to restore the disrupted hydro-balance: periodic water replacement in the amount of 20% of the total volume, providing the aquarium with active aeration systems, planting slow-growing plants and reducing the amount of fish food provided. The measures developed were efficient, they led to elimination of the outbreak of columnaris in the P. scalare and to restoration of biological equilibrium in a closed aquatic ecosystem.