When we think about disease management in our hatchery, we should bear in mind three main factors: fry, environment and pathogens. Our target is to have a healthy production system maintaining a balance between these three factors. Otherwise, the immune system will be affected by the imbalance between water quality, pathogen infection pressure or culture density, among others.

Article written by:

Raúl Benito Marco (Corporate Brand Manager Aqua at HIPRA).
Published on Hatchery Feed & Management, Vol 8, Issue 2, 2020.

The most important strategy for the establishment of a healthy system is Prevention. Prevention means the protocol suite that we establish in our hatchery before any health problems occur to avoid biomass and feed losses, overwork and treatments, loss of commercial value and delayed growth.

At HIPRA we believe in animal health prevention as the most effective strategy for keeping animals safe against pathologies and helping farmers raise their animals in a healthy and secure environment.

During our lives, we have found many situations where prevention is better than a cure. We know prevention involves some expense. But due to prevention, we reduce outbreaks in frequency and intensity, we decrease antibiotics use and biomass losses, we increase fish survival and we boost growth.

Figure 1. Cumulative mortality (%) after challenge with Vibrio anguillarum O1.

Figure 2. Daily average water temperatures during the trial. *Days post-vaccination: dpv. Days post-challenge: dpc.

Considering the expenses that are incurred when we have a disease outbreak, surely, we have a positive economic balance if we act before the outbreak occurs rather than after the problem has arisen.

Every investment that we make in our farms should have a return. Disease prevention is one of the investments with a quick return that we can make on our farms. We must point out three tools when talking about disease prevention: biosecurity, prophylactic baths and vaccination.

These three tools are a must if we want to keep pathogens away from our fish.

Vaccination to disease prevention

In this article, we want to focus on vaccination as it is the last barrier a pathogen will find before generating an outbreak on a farm. When working with live animals in an open farm system, the best biosecurity and prophylactic bath protocol can always have a weak point through which a pathogen can reach the fish. Vaccination is the best way to have immunized fish.

Vaccines ready their immune system to fight against one or more specific pathogens.

When carrying out vaccinations, in the first instance, it is very important to know which pathogens are causing or will cause mortality in our fish.Then we need to choose the correct vaccine containing the antigens that will generate immunogenicity against these problematic pathogens.

At HIPRA, we have a range of registered vaccines named ICTHIOVAC® against several pathogens that generate diseases such as vibriosis, pasteurellosis, lactococcosis, flexibacteriosis or nodavirus.

If you cannot find a solution to protect your fish within our ICTHIOVAC® range of vaccines, we can offer a tailor-made solution by developing an autogenous vaccine with the pathogens specificallyisolated on the farm that you want to vaccinate against.

For this purpose, we have the DIAGNOS department to monitor the health status of the farm and analyze the problematic pathogen.

Protection against vibriosis

A series of trials were performed, together with some customers, where the commercial vaccines from the ICTHIOVAC® range were used in European seabass (Dicentrarchus labrax).

In this trial, the protection of a commercial vaccine for vibriosis against a heterologous strain of Vibrio anguillarum was tested.

For this internal study carried out by HIPRA (study number EID-2019-0323), a group of 240 seabass injected intraperitoneally with a saline solution (PBS) was compared with a group of 240 seabass vaccinated with ICTHIOVAC® VR/PD vaccine against vibriosis by intraperitoneal injection (both at 0.1 ml dose/fish).

A challenge with a heterologous strain of Vibrio anguillarum (serotype O1) was performed in both groups 42 days post-vaccination. The average seabass weight at vaccination day was 14.96 g (± 3.45) in both groups, and at challenge day the PBS group weight was 38.92 g (± 10.23) and the ICTHIOVAC® VR/PD group weight was 33.82 g (± 8.7). During the trial, the temperature was optimal for seabass culture, at 21 ºC (± 2).

The challenge results showed that the PBS group suffered a 95% mortality at day five post-challenge, and the ICTHIOVAC® group survived 100% (Fig. 1).

Figure 3. Cumulative mortality (%) after challenge with Vibrio anguillarum O2β.

Protection under adverse temperature conditions

The vaccine was also tested under adverse temperature conditions on seabass to see their immune response against a Vibrio anguillarum challenge (Sánchez-Matamoros and Díaz, 2018).

Two groups of 100 animals were tested each with an average body weight of 47.1 g (± 11.3). One group was injected intraperitoneally with PBS (0.1 ml dose/fish) and the other group was injected with ICTHIOVAC® VR/ PD (commercial vaccine against vibriosis) at the same dose.

To test the vaccine immunogenic response under adverse conditions, the temperature during vaccination and 21 days post-vaccination was set at 13.8 ºC (± 0.6) (Fig. 2). Afterward, a challenge was performed with a virulent heterologous strain of Vibrio anguillarum (serotype O2β) and the temperature was raised up to 20.8 ºC (± 1.1).

This means that from vaccination to challenge it was almost 290 degree-days, while the onset of immunity for this vaccine has been tested to be more than twice these degree-days. Mortality occurred mainly between two and five days after the V. anguillarum O2β challenge, with a cumulative mortality of 1.7% in the ICTHIOVAC® VR/PD group and 68.3% in the PBS group (Fig. 3).

In other words, Relative Percentage Survival (RPS) was 97.6% for the ICTHIOVAC® VR/PD group. This demonstrated the efficacy of this commercial vaccine against a virulent heterologous V. anguillarum strain under unfavorable conditions in accordance with the European Pharmacopeia criteria (RPS higher than 75%).

Conclusions

These trials show what could happen if we have a disease outbreak on the farm having unvaccinated fish.

In these cases, the vaccinated fish immune system was able to fight against a virulent Vibrio anguillarum pathogen, which caused very reduced mortality, unlike unvaccinated fish.

With a correct vaccination program on the farm, fish can cope with a virulent pathogen, reducing the threats that bring down production rates. In other words, vaccination gives an added value to our fish.

REFERENCES:

¹Sánchez-Matamoros A., Díaz E. Efficacy of Icthiovac® VR/PD against Listonella anguillarum in sea bass under unfavorable conditions. Poster presented at: WE’R AQUACULTURE 2018, World Aquaculture Congress and European Aquaculture Congress. 2018, August 25-29. Montpellier, France.

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