What happens when fish get ich immunity?

[yheartsp]

I mean, i understand that when fishes gain an immunity to marine ich, they do not show the symptoms ( white spots, flashing etc )

but why?

why don't we see this
''2. Only time a human can see this parasite with the naked eye is when it is ‘pregnant’ on the fish and has formed a white nodule. (The white spot about the size of a grain of table salt or sugar).''

[leebca]

Ornamental marine fishes have an immune system that lies between the immune systems of land animals and invertebrates with regards to strength and complexity. Almost all of an invertebrate's immunity resides in the organism's innate immunity. The complex immunity of humans is greatly dependent upon our innate AND adaptive immune systems.

In layman's terms, there are two basic types of immunity. One is innate. This means the immunity doesn't care what the offensive organism or protein is, it will resist it or destroy it. (NOTE: although most immunity is towards a group of molecules most of which are proteins or protein-like, immunity may be towards other kinds of molecules. I use the word protein here to represent them all.)

The other immunity is called adaptive. This is where the immune system specifically recognizes the 'enemy' and is built to destroy that one enemy. The human T and B cells play various rolls in the human and animal adaptive immune system.

Protein serums made from Marine Ich have been used to make injections used to immunize marine food fishes against Marine Ich. It encourages the adaptive immune system to specialize in killing Marine Ich parasites. This is done by creating immunity to the proteins the Marine Ich uses to penetrate through the mucous coating and into the skin of the fish.

But, the downside is what I began with. The immune system of invertebrates is mostly innate. The immune system of the land animals is strongly both innate and adaptive. Marine fishes have an innate and adaptive immune system, but the adaptive one is 'weak.'

When marine food fishes are immunized against Marine Ich, that immunity lasts a few months to two years, based upon published data. The cost of the serum is very high. Most 'fish farms' don't use it. Hobbyists would hardly catch their pet fishes and stick them with needles, even if they could afford the inoculate. And in the end, the fish would only be immune for a few months (most likely) and then only immune to one parasite. The fish farming industry does get an advantage -- fewer losses occur in the immunized fish population, so injection may be attractive when handling young adult or fry.

But what part of this relates to your question? When injected, are the fish really free of the parasite or is it subdued? Much of the fish's effort against the parasite is to subdue it. But injected immunity is better than a naturally developed adaptive immunity. The fish can't be seen to have any symptoms. Skin scrapes, fin clips, etc. don't show the parasite's presence -- usually.

So now, we move to a second scenario. Naturally developed adaptive immunity to Marine Ich. Within the fish family, different species have different immune abilities to be adaptive to Marine Ich. Their innate immunity occurs in the mucous membrane where the Marine Ich first attacks. The reason why (in part) that Tangs get Marine Ich infections so easily is because their mucous coating is thin and not well suited to ward off the Marine Ich parasite.

On the other hand fishes like Mandarins have a really good mucous coating where their innate immune system is strong enough to reach the level of 'resisting' the Marine Ich parasite. Mandarins though do still get infected. Captive Mandarins aren't nourished properly and their mucous coating (and immunity) is compromised, making them susceptible to parasites and diseases.

My personal opinion is that Natural Selection selected the Mandarin based upon such resistance since that fish moves slowly and spends most of it life on the substrate where Marine Ich multiplies and seeks its next host. The Tang however lives in the open ocean, traveling up to 25 miles a day -- what Marine Ich parasite can catch a Tang in the ocean? But once the Tang is held captive in our aquarium, the parasite has a readily available feast at hand.

Do wild fishes with a natural adaptive immunity to Marine Ich show symptoms of the disease? Yes they do. Their skin scrapings, fin clips, etc. show the presence of the disease and sometimes spots are visible.

Now -- about the captive marine fish. . .Does the captive fish naturally develop an adaptive immunity to Marine Ich? and if so, will the infection still be seen? From what I've written so far the answer to the first question is clearly, "Yes." Our fishes can develop a natural adaptive immunity to the Marine Ich parasite. Some do and again, to various degrees. Much depends on how well the fish is cared for, fed, other present stressors, etc. This is why well fed fishes in top water quality and a great environment can still live with Marine Ich in our tank. They are infected, but still alive. They are in their survival mode, NOT in their thriving mode: Survive or Thrive?

The natural adaptive immunity has similarity to the immunization immunity. The immune system develops a specific immunity to a protein or group of proteins specific to the Marine Ich parasite. This immunity goes into the mucous coating of the fish (another reason why the Tang has a harder time to develop immunity to the parasite) and is also systemic (in the blood). When the parasite comes to the fish and tries to break through the mucous coating and into the fish, the fish's immune system blocks, and/or alters the parasite's chemicals. Depending on how effective this immunity is, the fish is either immune or resistant to the parasite.

Unfortunately, such immunity or resistance is temporary. It may be better/stronger in the injected fish, but the natural adaptive immunity is poor in quality (by human comparison).

When our fishes are held captive for a time in our aquarium and a new fish is added, suddenly all the diseases and parasites our captive fishes have had some adaptive immunity towards, can kill our pets. Even new bacteria brought in by the recent addition can create big health problems for the long-term captive fishes. They've lost their adaptive immunity and their innate immunity is weakened by captivity. This is the 'unspoken reason' why new acquisitions need to be quarantined.

Another good example is when there is a sudden temperature drop in the aquarium with fish that have a natural adaptive immunity to the parasite. When the temperature drops, the mucous coating of the fish suffers. This leads to a reduced ability to fend off the parasite (which is there, remember, but just not prolific). The hobbyist then sees, "The temperature dropped last night and now my fish are displaying Marine Ich spots." The hobbyists wonder why without understanding that the parasite was there and that the fish's immunity was just hanging on in the war against the parasite. The drop in temperature shifted the war to the side of the parasite winning.

It takes a lot of energy for the fish to maintain its immunity. Maybe that is why Nature never gave them much in this area. Their energy goes towards procreation when excess resources are available. They produce hundreds of eggs or offspring unlike the few most land animals produce. So a great immune system is compensated by having hundreds of offspring!

Unfortunately, all this good info above leads some lazy hobbyists into thinking, then the way to keep fish is to keep the disease in the aquarium! Don't even think of going there. . .Keeping diseases in our aquarium is NOT the way to help our fish. They will be in constant survival mode. They will be stressed, spending energy to survive. They will not enjoy what thriving has to offer. This is considered by the professionals to be poor animal husbandry.

Now, during their phase of being immune to Marine Ich, a spot may now and then show up. So your original perspective that nothing is displayed is not always true. Sometimes a spot does show up now and then. Even more than a hundred spots may show up. They may be smaller than if they weren't having difficulty with the fish's immune system. Even in such cases, the fish doesn't show any other signs of infection OR maybe it flashes a bit more than an uninfected fish. The other extreme is like you think -- nothing may be visible. But if I take one of those fish and examine skin scraping, fin clips, etc. under a microscope I can find Marine Ich parasites present.

The white spots don't become apparent because the parasite is taking short cuts to survive -- not leaving the fish is one such short cut. Another is residing in the gills where the skin is not such a physical barrier. But these fish are infected and their energy is diverted to trying to control the infection. These fishes are surviving day to day, but not thriving. The misunderstanding by the hobbyist is in not understanding the poor quality of fish immunity. Hobbyists think of fish immunity like human immunity, but they are far apart.

I hope the above helps. Remember that I haven't written in technical terms and some statements are not technically sound. But the point was to give a general understanding to a very technical subject and still to provide you with some understanding and background to the answer to your question.

[yheartsp]

wow, your explanations were wonderful and clear. i have a much better understanding towards a fish's immunity now, your understanding towards this field is unparalleled! hmmmm many people should read the above ! :eek3:

Anyway , Thanks again ! ( you helped my maroon to recover from ich if you remember ) xD

Here's a picture of him now, grown 2 inches since i got her , it's been half a year.



Then, In the QT

[leebca]

Thank you for your kind words.

The fish looks really well. Thanks for reminding me. I usually don't get to see the results!