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Discussion Starter · #1 ·
I have always wondered how an illness with one fish will effect others and how do they spread?

Can a single fish be sick in an aquarium yet others be perfectly fine? If so why? I know ich is one of those that can easily spread like wildfire and I understand how the parasite life cycle works. But find myself lost when it comes to fungal or bacterial things.

Anyone know?
 

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Sometimes you have one fish that's sick because it was stressed enough for the pathogens to take hold. If the other fish aren't stressed enough, though, sometimes they can fight it off enough that they don't show any symptoms. They aren't perfectly fine, they're infected and will start to show symptoms if stressed enough to let the pathogen take hold, but they appear to be entirely healthy.
 

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Someone correct me if I'm wrong but pretty sure all pathogens are present in a tank at all times. Just like with people, when a fish becomes stressed or weak for whatever reason, its immune system gets low, making it more susceptible to becoming infected. This does mean an infected fish will raise the amounts of pathogens in the water, but doesn't mean all the fish will become infected. Unfortunately most aquarium treatments have been under dosed, and over used for so long, they are no longer very effective. The best medicine is always preventative maintenance and optimal nutrition for the fish.
 

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With proper quarantining, it is theoretically possible to keep an aquarium free of most pathogens. It isn't often done, though, so yes, an aquarium is usually infected with a few things. It's why it's so vitally important to never release aquarium fish, because wild fish have no built-up resistance to the pathogens that are so common in our aquarium industry.
 

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Children Boogie
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Someone correct me if I'm wrong but pretty sure all pathogens are present in a tank at all times. Just like with people, when a fish becomes stressed or weak for whatever reason, its immune system gets low, making it more susceptible to becoming infected. This does mean an infected fish will raise the amounts of pathogens in the water, but doesn't mean all the fish will become infected. Unfortunately most aquarium treatments have been under dosed, and over used for so long, they are no longer very effective. The best medicine is always preventative maintenance and optimal nutrition for the fish.
yes and no.
Not all pathogens are present. You can introduce virulent pathogens like columnaris by introducing fish etc... But yes, healthy fish can fight off basic bacterial & fungal infections.
 

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Discussion Starter · #7 ·
But if we can agree that strong healthy fish cam carry but not show symptoms similar to a human with cold virus but no symptoms. That how does quarantining help? Would the pathogens eventually go away?.
 

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Fish and all other animals have an immune system. When something (bacteria, virus, fungi, parasite) attack their body their body responds with ways to fight off the invader. In fish, the slime coat is the first layer of defense. The fish can shed extra slime coat when a parasite attacks, and this often sheds the parasite, too. I think this is part of the reason Ich does not kill its hosts in the wild- far fewer Ich organisms, and the fish can get rid of the few that reach it. But in an aquarium the concentration of Ich organisms is way higher, and the fish immune system cannot cope with that many.
This response may be strong when the fish is healthy (proper nutrition, correct water parameters) or weak if the fish has been stressed (poor living conditions, competition from tank mates, poor food, other recent illness and other reasons).

The invading organism lives in the fish the same as similar organisms live in us or any other animal. Takes nutrition from the host, grows, reproduces.
Each organism has its own way of reproducing, but they all do reproduce. Depending on the organism the 'babies' might be spores, or any of several other terms.
When these reproductive cells contact a host they start growing.

Most disease causing organisms in fish spread via the water. That is, at some part of their life cycle they spend some time drifting free in the water. Thus, a UV sterilizer can help against many different infections. Water changes will reduce the population of free-swimming organisms. I think some free swimming organisms may concentrate in low flow areas of the tank, such as in a cave or under an arch of wood or similar places that the fish tend to hang out. The fish shed some of the reproductive phase of the disease or parasite, and poor water movement does not flush them away, so the next fish that rests in this hide-away has a larger population of disease or parasite organisms to deal with. Some organisms need to be eaten by the host before they can infect the host. Many internal parasites are like this. Some diseases are like this. Very little spread while the first host is alive, but rampant spreading once the host is dead. Either the disease organism leaves the dead host and drifts in the water, or else the dead host is eaten by the other fish, which then get sick. Neon Tetra Disease is like this. Sure, it can spread through the water. But it spreads a lot faster if the dead fish is eaten by the other fish.

Most diseases can be spread from tank to tank on shared tools and equipment, especially if the tool is carried wet from one tank to the next. Dipping the tool in a disinfectant between tanks can go a long way in minimizing the spread of infection. Having separate tools (especially for a hospital or quarantine tank) can prevent the spread.
Washing your hands between tanks can help.
When you buy new fish put them in a quarantine tank for a month to make sure they are not carrying any disease or parasite. You can treat them in the quarantine tank as needed so your display tank stays free of most diseases and parasites.
Many aquatic organisms cannot tolerate drying out, but this varies, and I would not trust this as the only method of reducing the spread of diseases via tools.
 

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The main benefit of quarantining is being able to weed out any unhealthy specimens, and if appropriate treat as necessary before putting fish into an established tank. Also since quarantine tanks are generally small tanks, water changes with a larger volume are easy, and medication cost are greatly reduced. Having worked in an aquarium store for 15 years, I wish I had a dollar, for every time someone started treating a 75+ with medication. Since many times a second round must be administered, or the medication changed, it can cost 75 to 100 dollars on a large tank! Could have done it with $10 in a small quarantine tank.
 

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Discussion Starter · #13 ·
So how does a fish with columnaris make it to our tanks. From my understanding this gram negative disease is a fast killer and generally hard to miss in terms of fish appearance and symptoms.

So if fish are being shipped to the stores and they have columnaris I would imagine they would all die or loom terrible before hitting the cash register.
 

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Children Boogie
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There's probably an incubation period before you see the visual signs. That's why quarantine period is usually a month.
The columnaris could be at the petstore too so they won't get infected till the store.
 

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Discussion Starter · #15 ·
Just read this about columnaris..
Its name is derived from columnar shaped bacteria, which are present in virtually all aquarium environments.

The columnaris bacteria are most likely to infect fish that have been stressed by conditions such as poor water quality, inadequate diet, or stress from handling and shipping. Columnaris can enter the fish through the gills, mouth, or via small wounds on the skin. The disease is highly contagious and may be spread through contaminated nets, specimen containers, and even food. For this reason it is important to use sterile techniques to avoid contaminating other tanks.


So apparently it's in all aquariums.
 

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Here is one possible scenario:

Perhaps there are some columnaris organisms in the water, and the fish have only JUST been infected. They are not showing any symptoms, yet.
Then you add the water to your tank, and the disease is in the tank.

Now... maybe... the new fish is healthy, and the stress of capture, transport and so on does not affect it enough that the Columnaris can establish.
But maybe there has been a problem in your main tank, and for whatever reason, some fish are more susceptible. They get sick, but the new fish does not.

This would be prevented by placing the new fish in quarantine. This would be minimized by not adding the store water to your tank, but netting the fish out of the bag.
 

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Children Boogie
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Yes and no on the columnar bacteria. It might be common but the strain that kills isn't unless introduced. Like the antibiotic resistant staff bacteria that kills people can be found in hospitals but is generally common everywhere


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