Many fish vaccines developed in Europe and America are still being tested on different other species. The challenge to vaccine development for fish is because fish lack memory and rely more on the innate immunity, where the effect of vaccination is only short lived and the need for repeated administration, which costs money (dipping or IP injection). Most vaccines are also very specific to the pathogens targeted, although increasingly, vaccines are now emerging which act on a relatively broad spectrum.

The type of vaccine which holds promise (in my view) and which could be mass produced at affordable costs are those which utilize live bio-engineered microorganisms as vectors for the expression of surface proteins or expressing antigens against pathogens. However, legislation limiting the use of GMO (including microorganisms) is the main impediment to their application, as most countries adopt the EU standards on the use and application of GMO to our food chain.

I cannot say about India but I know that elsewhere, efforts are still on-going to develop cheap vaccines for the majority of fish pathogens. Right now in my lab, we are at advanced stage applying for a patent for one that has been under development during the last 4 years, for some marine species in Asia (Grouper, Barramundi). Hopefully when it is approved, we can target India ^_^

Its not the question of India alone, its in most part of Asia except a few commercial vaccines in Japan and Korea for Olive Flounder. The main reason is the the species we culture in Asia. Most of them are not high valued fish and vaccination is not cost effective unless it is a cheap oral vaccine and we can always compensate the loss due to diseases by growing extra fish. In Salmonid aquaculture, its a different story, the fish is highly valued and the cost of vaccine can be easily recovered.

Dear Mohammed Aliyu-Paiko, I agree and disagree with your observations. Agree, that we have aquaculture species where cost-effectiveness is at the top as rightly pointed out by Vinay. I worked in develping a biofilm vaccine against motile Aeromad infections, it was amply demonstrated that the protection lasts over almost a year which is good enough for a crop of one year. But the cost factor pulls back the commercialization aspect of vaccines in India and other Asian countries. But the mariculture could be a different story.

I disagree, that fish lack memory!!! Many experiments have proved that the fish produced memory cells as evident from a sharp and high secondary (booster responses). Even in the case of oral vaccine primed for 15 days and boosted for 15 days at a 15 day gap proved highly effective. Probably you have missed a point.

Sure I may have missed, one or two? That is why we are here (to learn), right?

Memory in fish for how long, a few days, weeks, months, a year? Pls show me a few evidences (available commercial vaccination on sale). Recall, when chickens are vaccinated against any disease, it is usually once (except where there is a problem) until harvested, sold out and eaten. Likewise cows, goats, dogs, humans? Memory cells once activated will always keep track in mammals.

At best fish vaccines (the ones in commercial use now, which have been proven to be successful) last how long?,15 days? the reason for the need for re-vaccination if the production cycle goes beyond certain periods? I am talking about memory activation throughout production cycle (which in fish lasts 6months to 2 years or more, depending on what species one is rearing)

I am aware of claims made in the literature that fish fish have memory but this claim is yet to be proved with a working vaccine against any disease to be administered once like in terrestrial animals i used as example earlier.

The antibody titres produced by fish are relatively very low, their affinity low and their diversity also very low compared to that for mammals (the number of proteins responsible for fish are far fewer). Production of fish antibodies is temperature, species and antigen dependent and that is why the CHASE is still on. This is without mentioning the effects of diets (omega 3 HUFA synthesis in freshwater vs marine species), stress level, genetic variability, age and physiological stage of the species, all of which also affect antibody production during immuno stimmulation.

I may have sounded very pessimistic (or unscientific even), when I said fish have NO memory (that is far from true), but in effect I was making comparisons to mammals. If this is ignorance, then I am not alone because Prof Kim D. Thompson, a foremost vaccines expert on Atlantic salmon (University of stirling, our collaborator) still echoed this same message at our workshop 2 months ago. I believe it is for the same reason that in the literature, the phrase "fish rely more on innate than adaptive immunity" is still relevant or for that matter, the reason why the administration of multivalent vaccines to a species of fish during one production cycle is still popular. I am hoping that would change very soon because of the losses suffered in the industry due to this challenge.

Here, we bio-engineered a strain of Lactococcus lactis as a vector against vibriosis and are testing its efficacy against 4 vibrio pathogens. So far it works against 2 but we are still conducting trials, including induction of memory cells.

You have some information that we can benefit from, please feel free to share it.

Thank you for your contributions.

Just a few remarks about memory formation in fish. There is enough evidence, that bony fish develop specific immunological memory. The success of available vaccines for salmonids is based upon this. In basic studies in the laboratory you can see, that memory can last for several months and in some cases more than a year. Of course, there are differences with mammals. In general, fish need more time (several months) to develop optimal memory. Optimal priming antigen doses are often low. The reason, that some investigators are sceptical about memory is fish, is probably the fact that too high priming doses were used an a challenge relatively early after priming (e.g. 14 days). These are schemes, that will work in mammals, but not in fish. In practice, fish should not be vaccinated at a very early age, because tolerance can be induced (see attachment). There is also an excellent review on B cell memory by Steve Kaattari (Ann. Rev. Fish Dis., 2, 161-180, 1992). He shows, that in teleosts B-cell memory is due to an increase in antigen-sensitive precursor cell pool without any of the accompanying characteristics observed in mammals such as a switch in isotype or affinity maturation.

Taken together you can say, that the possibilities for developing effective vaccines for warmwater fish (e.g. cyprinids) in India are there. However, a vaccine alone is usually not enough. A lot can be achieved as well by selecting disease resistant fish strains or simply by preventing stress in aquaculture.

Hope this paper is of some use to know about problems and challenges to develop vaccine for asian aquaculture.