A. P. Desbois
3.7 A POSSIBLE VACCINATION PROGRAM FOR FISH IN LAND-BASED IMTA SYSTEMS
Diseases in Nile tilapia, Asian sea bass, and groupers have been reviewed elsewhere (Shoemaker, Klesius, and Evans 2000; Kasornchandra 2002). Several types of vaccines for diseases of known pathogens are listed in Table 3.2. For effective protections, the vaccination programs should be for protection against diseases frequently observed in the local areas.
TABLE 3.2
Vaccines for Protection against Common Pathogens in Land-Based IMTA Commercial Fish
Pathogen Type
Administration
Route References
For Seawater Nile Tilapia (oreochromis niloticus) S. agalactiae Attenuated vaccine Intraperitoneal Liu et al. (2019)
Recombinant vaccine Oral Nur-Nazifah, Sabri, and Siti-Zahrah (2014)
DNA vaccine Oral Zhu et al. (2017)
Inactivated vaccine (whole-cell, formalin-killed)
Intraperitoneal Evans, Klesius, and Shoemaker (2004)
S. iniae Attenuated vaccine Intraperitoneal Miccoli et al. (2021)
DNA vaccine Intramuscular Kayansamruaj et al. (2017) Attenuated vaccine Intracoelomic Heckman et al. (2022)
A. hydrophila Inactivated whole bacteria Intraperitoneal Ruangpan, Kitao, and Yoshida (1986) Attenuated vaccine Intraperitoneal Pridgeon, Klesius, and Yildirim-Aksoy
(2013) S. iniae and V.
vulnificus
Inactivated whole bacteria Intraperitoneal Shoemaker, LaFrentz, and Klesius (2012)
V. vulnificus Inactivated whole bacteria Intraperitoneal Shoemaker, LaFrentz, and Klesius (2011)
V. harveyi Inactivated whole bacteria Intraperitoneal Abu Nor et al. (2020)
E. tarda Recombinant vaccine Intraperitoneal Pridgeon, Klesius, and Yildirim-Aksoy (2013)
F. Noatunensis subsp.
Orientalis (Fno)
Inactivated vaccine (formalin-killed Fno vaccine)
Intraperitoneal Pulpipat et al. (2020) Inactivated vaccine (whole-cell) Intraperitoneal Shahin et al. (2019) TiLV Inactivated vaccine (formaldehyde- and
β-propiolactone-inactivated vaccines)
Intramuscular Zeng et al. (2021)
DNA vaccines Intramuscular Yu et al. (2022)
(Continued)
40 Fish Vaccines
3.7.1 VaccInesfor seawater nIle tIlapIa
Streptococcosis, one of the most common infectious bacterial diseases of farmed Nile tilapia with high mass mortality, is caused by Streptococcus spp. infections. Vaccines protecting tilapia (and other kinds of fish) against a number of bacterial diseases have been developed and commercial- ized, for example, S. iniae (AQUAVAC® Strep Si, MSD; Vaxxinova®, International BV; Himmvac Agilban-S Plus® and Himmvac Agilban S-3 Plus®, KBNP Inc.) and S. agalactiae serotypes Ib and III (AQUAVAC® Strep Sa1, MSD; Vaxxinova®, International BV). In one report, tilapia receiving the vaccine against S. iniae had a significant rise in specific antibody levels and relative percent survival (RPS) of 100% by intraperitoneal injection, and 88% by immersion vaccination (Miccoli et al. 2021). Likewise, an attenuated erythromycin-resistant S. agalactiae vaccine produced a sig- nificant rise in antibody titers, which protected the fish for at least 16 weeks after vaccination (Liu et al. 2019). This period of protection is long enough for the fish to grow to marketable size without the need for a booster vaccination. DNA vaccine against the disease was tested but not yet com- mercialized and was found to stimulate both innate and adaptive immunity (Evensen and Leong 2013; Kayansamruaj et al. 2017; Mondal and Thomas 2022). The feed-based recombinant vaccine against S. agalactiae in red tilapia displayed a high IgM antibody titer in serum, mucus, and gut of the vaccinated fish, with RPS at 70% following the challenge (Nur-Nazifah, Sabri, and Siti-Zahrah 2014). Using recombinant proteins to produce the vaccine would probably lower the cost of vac- cines; however, its effectiveness also needs to be considered.
Vaccines against two other types of bacteria, Aeromonas hydrophila and Edwardsiella tarda, have been developed with high protective efficiency (Pridgeon, Klesius, and Yildirim-Aksoy 2013).
Both vaccines were designed for intraperitoneal administration and 100% protection was reported (Pridgeon and Klesius 2011).
TABLE 3.2 (continued)
Vaccines for Protection against Common Pathogens in Land-Based IMTA Commercial Fish
Pathogen Type
Administration
Route References
For Asian Sea Bass (Lates calcarifer) S. iniae Inactivated vaccine (formalin-killed
bacterins)
Intraperitoneal Aviles et al. (2013)
V. anguillarum DNA vaccine Intramuscular Kumar et al. (2007)
V. harveyi, S. agalactiae and A. hydrophila
Polyvalent vaccine (formalin-killed vaccine)
Oral Mohamad et al. (2021) S. agalactiae and S.
iniae
Inactivated vaccine (oil-based formalin-killed bivalent)
Intraperitoneal Lan et al. (2021)
NNV DNA vaccine Intramuscular Vimal et al. (2016)
For Grouper (epinephelus spp.)
V. vulnificus Inactivated whole bacteria Intraperitoneal Hoihuan et al. (2021) V. harveyi Glutathione peroxidase (GPx) DNA
vaccine
Intramuscular Wang et al. (2017) Recombinant vaccine (outer-membrane
protein)
Intramuscular Zhu et al. (2019) Attenuated vaccine Intraperitoneal Bai et al. (2020) V. alginolyticus Attenuated vaccine Intraperitoneal Pang et al. (2018, 2022)
NNV DNA vaccine Intramuscular Chen, Peng, and Chiou (2015)
β-Propiolactone (BPL) inactivated virus and formalin-inactivated virus
Intraperitoneal Ou-yang et al. (2012)
Aquaculture 41
Vibriosis has been rarely reported in farmed tilapia in Thailand, and when it does occur, it is mostly red tilapia that is affected. A formalin-killed V. harveyi vaccine was found to promote strong IgM antibody titers and lysozyme activities in red tilapia, which showed higher rate of survival upon challenging the fish with the pathogen, when compared to unvaccinated control fish (Abu Nor et al. 2020). Red tilapia vaccinated with a whole-cell vaccine against V. vulnificus infection had RPS values of 88% following bacterial challenge (Shoemaker, LaFrentz, and Klesius 2011).
Another type of bacteria that infects tilapia, especially red tilapia, is the intracellular bacte- ria, Francisella spp. This group of bacteria has attracted attention, since it was found in a large population of tilapia without causing any obvious disease manifestations. Red tilapia infected with F. noatunensis were found to be more susceptible to other diseases than the noninfected fish (Sirimanapong et al. 2018). At present, there is no commercial vaccine against these bacteria.
The main viral disease in tilapia is TiLV, but effective vaccine for TiLV is still in the process of being developed (Lertwanakarn et al. 2021). A DNA vaccine under development against TiLV had produced some promising results (Criollo Joaquin et al. 2019).
3.7.2 VaccInesfortHe asIan sea Bass
Several bacterial diseases affecting tilapia also affect Asian sea bass: Streptococcus spp., Vibrio spp., and A. hydrophila. Therefore, vaccines used against pathogens in tilapia are also applica- ble to Asian sea bass. The formalin-killed S. iniae bacterin vaccines provided 100% protection against the vaccine strain in vaccinated L. calcarifer, whereas significantly reduced protection was observed when the fish were challenged with a heterologous strain of the bacterium (Aviles et al.
2013; Caipang et al. 2014). An oil-based formalin-killed bivalent vaccine containing S. agalactiae and S. iniae promoted strong systemic and mucosal antibody responses in vaccinated Asian sea bass, with RPS of 85% obtained following challenge with both bacteria (Lan et al. 2021). Live attenuated V. harveyi provided RPS of 68% to L. calcarifer fingerlings (Chin et al. 2020). The feed-based polyvalent vaccine against V. harveyi, A. hydrophila, and S. agalactiae showed a sig- nificant rise in IgM antibody levels as well as the RPS of 75%, 80%, and 80%, respectively, after the challenge with the three pathogens (Mohamad et al. 2021). Likewise, DNA vaccines encoding an outer-membrane protein of V. anguillarum provided RPS of 56% after the challenge with the bacteria (Kumar et al. 2007).
A commercial vaccine for L. calcarifer is available for V. anguillarum (serotype 01) and Photobacterium damsela subsp. piscicida (causing pasteurellosis) (for immersion, ALPHA DIP®
2000, AQUAVET S.A; for intraperitoneal injection, ALPHA JECT® 2000, AQUAVET S.A.). In addi- tion, an autogenous vaccine against Aeromonas veronii has also been developed by the same company.
For viral infections in L. calcarifer, a DNA vaccine against NNV in L. calcarifer was tried with pFNCPE42-DNA, resulting in a RPS value of 77%, and a significant increase in the antibody titer in vaccinated fish (Vimal et al. 2016). An injectable vaccine against NNV in red grouper is also effec- tive against NNV in L. calcarifer (ALPHA JECT micro® 1 noda, AQUAVET S.A.).
3.7.3 VaccInesfor groupers (EpinEphElusspp.)
The most common disease in groupers is vibriosis, which is usually caused by V. harveyi and V.
alginolyticus infections (Mohamad et al. 2019). Viral infections have also been reported, due to iri- dovirus and NNV. A mixed formalin-killed cell vaccine of three subgroups of V. vulnificus biotype 1 was effective in protecting the brown-marbled grouper, E. fuscoguttatus, in Thailand (Hoihuan et al. 2021). In China, one study produced a RPS value of 78% with a live attenuated vaccine fol- lowing being challenged with a wild type V. alginolyticus strain HY9901ΔvscB in pearl-gentian or hybrid grouper (♀E. fuscoguttatus ×♂E. lanceolatus) (Pang et al. 2022; Pang et al. 2018). A gluta- thione peroxidase DNA vaccine was tested in China in 2017 for intramuscular administration, and it gave 78% RPS after being V. harveyi challenged (Wang et al. 2017), while a recombinant vaccine in
42 Fish Vaccines the hybrid grouper, constructed from the outer-membrane protein of V. harveyi, showed the protein to be a potential vaccine candidate (Zhu et al. 2019).
For viral infections, β-propiolactone- and formalin-inactivated virus vaccines were produced against Singapore grouper iridovirus (SGIV) that showed promising results for protecting orange- spotted grouper against the virus when challenged at 30 days post-vaccination with RPSs values of 92% and 100% obtained, respectively (Ou-yang et al. 2012). The oil-adjuvanted vaccine is commercially available (AQUAVAC® IridoV, MSD). In addition, mass mortality in grouper larvae caused by NNV infection could be prevented by DNA vaccine with modulated CpG oligodeoxy- nucleotide (Viral Nervous Necrosis Vaccine, Nisseiken Co., Ltd.) (Chen, Peng, and Chiou 2015).
However, NNV inactivated with 0.4 mM binary ethylenimine (BEI) or 0.1%–0.2% formalin in orange-spotted grouper larvae resulted in 95% RPS and 43% RPS, respectively, in vaccinated fish (Kai and Chi 2008). When the vaccine from the viral supernatant was injected intramuscularly into the potato grouper, E. tukula, broodstock, NNV-specific antibodies were found in eggs from vaccinated broodstock within 5-month post-vaccination. Moreover, NNV was detected in the eggs of the nonvaccinated fish, but not in the vaccinated fish. Therefore, the vaccination looked like it protected against the vertical transmission of the pathogen from the grouper broodstock (Kai et al. 2010).
It is interesting to find out the levels of innate and acquire defenses for the fish reared under the land-based IMTA, compared to those of the same species reared under intensive monoculture.
It is possible to set up the two groups of animals for this study in a scientific way. A net cage stocked with the fish at a commercial density, for example, at 30 individuals/m3, is placed in the IMTA ponds. The same species of fish outside the cage, at a density of 2 individuals/m3, are those under IMTA conditions. The fish in the cage are fed with commercial pellets but the fish outside the cage swim freely, interact with other aquatic species, and prey on their natural diet. But yet, the water conditions of the two groups are mostly identical.
To compare the efficacy of vaccines on the fish under intensive monoculture and those under the land-based IMTA, the same set-up as described, that is, a net cage in the IMTA pond, can be employed as well. At this point, it may be helpful to explain how the fish are prepared for stocking in the IMTA ponds. They are hatchery-produced and nursed in canvas tanks before being released into the pond. Seawater-acclimated O. niloticus are released at the size of 50 g; L. calcarifer, at the length of 6 in; and Epinephelus spp., at the size of 200 g. Therefore, vaccinations can be carried out at the time before releasing the fish into the pond. In these experiments, one group of the vac- cinated fish should be released into the net cages and the other group outside the cages. The choice of vaccine administration is preferably by intramuscular or intraperitoneal injections as these two methods of vaccine administration are most effective (Ismail et al. 2016; Silva et al. 2009). In this scenario, booster doses, if required, can be accomplished only through oral administrations since it would not be feasible to catch all the experimental fish in the pond for the booster-dose injection.