Jay Hemdal
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Fish Medic
I was working on some text this morning. Not enough for a full article (yet) so I thought I'd post it here for discussion:
Immunity in Fish
The ability for a fish to fight off a disease (or not) is based on the level of immunity it has. A physically stressed fish will have a lower immunity level and be more prone to developing disease. However, people tend to rely too much on immunity and they think that if they offer the fish a great diet, it will be (mostly) free of disease. Some people extrapolate that even further and think that if they have a sick fish, if they feed it well, they can cure it (the chicken soup syndrome). The reality is that fish have a less developed immune response than mammals do, and we know that with humans, even the best diet and exercise does not prevent all diseases and in some instances really doesn’t help much at all. Immunity varies between the parasite involved. Bacterial diseases are rarely communicable because the fish have good defense (skin structure) and good immunity against them. Fish don’t have much immunity against some parasites like Neobenedenia flukes.
Innate immunity – this is the fish’s genetic predisposition to being able to fight off infections using its normal antibody system. There are differences seen between species of fish, with the example of Achilles tangs being much more prone to developing Cryptocaryon infections than are yellow tangs. Innate immunity is the baseline level, the starting point and nothing really changes that in a given individual.
Immunity conferred by good diet/environment – Fish with lower stress levels will have better immunity. Keeping the fish in a stable aquarium, with no aggressive tankmates, good water quality and a great diet will help boost its immunity. However, people often fail to understand that the disease organism themselves can be a major stressor, and can override all immunity conferred by a good environment.
Acquired immunity – This type of immunity is mounted by a fish after exposure to (and survival from) some disease outbreak. Antibodies are created that help the fish fight off future infections from that disease organism. Too many times in aquariums, the fish does not survive the disease challenge, so no acquired immunity is possible. In most cases, the only functional benefit for this is seen with sub-lethal viral diseases such as Lymphocystis; a fish that recovers from that disease rarely acquires it again. Wild fish have very little acquired immunity by virtue of not being infected with disease organisms to a high enough degree (or if they are, they get eaten by predators due to their weakened state). Immune responses in fish seems strongest against viruses and least against multi-celled parasites such as flukes. Parasites living on the skin or gills of fish are less exposed to the antibodies, so acquired immunity to protozoans and metazoans such as Cryptocaryon, Amyloodinium and flukes is only partial and transient.
This diagram outlines the relationship between host, pathogen and environmental problems. Overlaps indicate problem areas, with the triple overlap in the center showing the almost certainty of disease when all three elements are combined. Notice however, that disease is still possible if hosts and pathogens are combined, even in the absence of any environmental issues. Likewise, environmental problems can harm the host even in the absence of pathogens.
Jay
Immunity in Fish
The ability for a fish to fight off a disease (or not) is based on the level of immunity it has. A physically stressed fish will have a lower immunity level and be more prone to developing disease. However, people tend to rely too much on immunity and they think that if they offer the fish a great diet, it will be (mostly) free of disease. Some people extrapolate that even further and think that if they have a sick fish, if they feed it well, they can cure it (the chicken soup syndrome). The reality is that fish have a less developed immune response than mammals do, and we know that with humans, even the best diet and exercise does not prevent all diseases and in some instances really doesn’t help much at all. Immunity varies between the parasite involved. Bacterial diseases are rarely communicable because the fish have good defense (skin structure) and good immunity against them. Fish don’t have much immunity against some parasites like Neobenedenia flukes.
Innate immunity – this is the fish’s genetic predisposition to being able to fight off infections using its normal antibody system. There are differences seen between species of fish, with the example of Achilles tangs being much more prone to developing Cryptocaryon infections than are yellow tangs. Innate immunity is the baseline level, the starting point and nothing really changes that in a given individual.
Immunity conferred by good diet/environment – Fish with lower stress levels will have better immunity. Keeping the fish in a stable aquarium, with no aggressive tankmates, good water quality and a great diet will help boost its immunity. However, people often fail to understand that the disease organism themselves can be a major stressor, and can override all immunity conferred by a good environment.
Acquired immunity – This type of immunity is mounted by a fish after exposure to (and survival from) some disease outbreak. Antibodies are created that help the fish fight off future infections from that disease organism. Too many times in aquariums, the fish does not survive the disease challenge, so no acquired immunity is possible. In most cases, the only functional benefit for this is seen with sub-lethal viral diseases such as Lymphocystis; a fish that recovers from that disease rarely acquires it again. Wild fish have very little acquired immunity by virtue of not being infected with disease organisms to a high enough degree (or if they are, they get eaten by predators due to their weakened state). Immune responses in fish seems strongest against viruses and least against multi-celled parasites such as flukes. Parasites living on the skin or gills of fish are less exposed to the antibodies, so acquired immunity to protozoans and metazoans such as Cryptocaryon, Amyloodinium and flukes is only partial and transient.
This diagram outlines the relationship between host, pathogen and environmental problems. Overlaps indicate problem areas, with the triple overlap in the center showing the almost certainty of disease when all three elements are combined. Notice however, that disease is still possible if hosts and pathogens are combined, even in the absence of any environmental issues. Likewise, environmental problems can harm the host even in the absence of pathogens.
Jay
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