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Many Aeromonas species are infecting striped catfish in the Mekong Delta in Vietnam. This study aimed to evaluate the effectiveness of autogenous vaccines developed by analysing the genetic diversity through DNA fingerprint analysis. A total of 38 Aeromonas strains isolated from 2017 to 2022 were analysed for phenotypic differences using the repetitive element sequence PCR (rep-PCR) with the (GTG) 5 single-primer. The vaccines were water-in-oil emulsion whole-cell inactivated with two monovalent vaccines containing antigens of Aeromonas VH31 (VC-VH31), or Aeromonas VH74 (VC-VH74) and a bivalent vaccine with both Aeromonas VH31 and VH74 (VC-VH31/74). The experiment lasted for 60 days in water at 28 °C and was performed in triplicates. Blood samples were taken at 0, 15, 30, 45 and 60 day post vaccination (dpv) to collect the serum. The challenge infection was performed as a co-infection immersion challenge of two homologous strains of Aeromonas VH31 and Aeromonas VH74 at dose LD 60 value 0,55 × 10 7  cfu/mL and 0,47 × 10 8  cfu/mL, respectively. The highest relative percent of survival (RPS) of the VC-VH31/74 bivalent vaccine was 100 % and the fish displayed no clinical signs of disease. At 30 dpv, the concentration of total leukocytes, lymphocytes, monocytes and granulocytes was highest in the group receiving the dual vaccine. Additionally, the results showed that the difference between the vaccines was significant when ELISA analysis of IgM-specific antibodies in serum, and the result was highest in VC-VH31/74 bivalent vaccine after 30 days (p < 0.05) and remained stable until 60 dpv. The vaccine showed good immunogenicity and high protective efficacy against Aeromonas spp. in catfish. Thereby demonstrating the potential of Aeromonas autogenous vaccine use., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

The development and growth of fish farming are hindered by viral and bacterial infectious diseases, which necessitate effective disease control measures. Furunculosis, primarily caused by Aeromonas salmonicida, stands out as a significant bacterial disease affecting salmonid fish farms, particularly rainbow trout. Vaccination has emerged as a crucial tool in combating this disease. The objective of this experiment was to assess and compare the efficacy and duration of different vaccine protocols against furunculosis in large trout under controlled rearing conditions, utilizing single and booster administrations via intraperitoneal, oral, and immersion routes. Among the various vaccination protocols tested, only those involving intraperitoneal injection, administered at least once, proved truly effective in preventing the expression of clinical signs of furunculosis and reducing mortality rates. A single intraperitoneal administration provided protection for up to 2352°-days, equivalent to approximately 5 months in water at 16 °C. However, intraperitoneal vaccination may lead to reduced growth in the fish due to resultant intraperitoneal adhesions. Additionally, protocols incorporating booster doses via intraperitoneal injection demonstrated efficacy regardless of the administration route of the primary vaccination. Nevertheless, the use of booster vaccinations via the intraperitoneal route did not confer any significant advantage over a single intraperitoneal injection in terms of efficacy., Competing Interests: Declaration of competing interest None., (Copyright © 2024. Published by Elsevier Ltd.)

Atypical Aeromonas salmonicida (aAs) and Vibrionaceae related species are bacteria routinely recovered from diseased ballan wrasse used as cleaner fish in the Atlantic salmon farming industry. Autogenous (i.e. farm specific inactivated) multivalent vaccines formulated from these microorganisms are widely used to protect farmed wrasse despite limited experimental proof that they are primary pathogens. In this study, the components of a commercial multivalent injection vaccine containing four strains of Aeromonas salmonicida and one strain of Vibrio splendidus previously isolated from ballan wrasse in Scotland, were tested for infectivity, pathogenicity and virulence via intra peritoneal injection at pre-deployment size (25-50 g) and the efficacy of the vaccine for protection against aAs assessed. Injection with 3.5 × 10 9 , 8 × 10 9 1.8 × 10 9 and 5 × 10 9  cfu/fish of Vibrio splendidus, V. ichthyoenteri, Aliivibrio logeii and A. salmonicida, respectively, did not cause significant mortalities, lesions or clinical signs after a period of 14 days. IP injection with both aAs and Photobacterium indicum successfully reproduced the clinical signs and internal lesions observed during natural outbreaks of the disease. Differences in virulence (LD 50 at day 8-post infection of 3.6 × 10 6  cfu/fish and 1.6 × 10 7  cfu/fish) were observed for two aAs vapA type V isolates. In addition, the LD 50 for Photobacterium indicum was 2.2 × 10 7  cfu/fish. The autogenous vaccine was highly protective against the two aAs vapA type V isolates after 700-degree days of immunisation. The RPS FINAL values for the first isolate were 95 and 91% at 1 × 10 6  cfu/fish and 1 × 10 7  cfu/fish, respectively, and 79% at 1 × 10 7  cfu/fish for the second isolate tested. In addition, significantly higher anti aAs seral antibodies (IgM), were detected by ELISA in vaccinated fish in contrast with control (mock vaccinated) fish. These results suggest wrasse can be effectively immunised and protected against aAs infection by injection with oil adjuvanted vaccines prepared with inactivated homologous isolates., (Copyright © 2020 Elsevier Ltd. All rights reserved.)