What does quarantining a new fish mean?
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Andy Sager
Aquarium Advice Addict
One of these days I need to rewrite an article on quarantining fish that was lost on a defunct computer and now resides in an untrusty forum. 
But here we go
The oxford dictionary defines quarantine the following way:
noun
1. a state, period, or place of isolation in which people or animals that may have been exposed to infectious disease are placed.
"horses entering the country must stay in quarantine longer"
verb
1. place (a person or animal) in quarantine in order to prevent the spread of an infectious disease.
"I quarantine all new fish for one month"
From a TFH article:
For some, it’s because they’re too impatient to wait out a quarantine period; they want that new fish in their tank now! For others, it’s an unwillingness to invest money and time in a tank they’re not going to use regularly. Some hobbyists seem to think the concept of quarantine is overblown; a disease outbreak, they believe, is something that happens to other people’s tanks, never their own. And of course there’s the unexpected acquisition—the fish that, say, your nephew wins at the fair, or the species we’ve been searching for that suddenly appears in our local fish shop. If we don’t buy it now, we rationalize, who knows when we’ll find it again—and, besides, it looks healthy. So why not take our chances?
To answer that question, here’s a horror story courtesy of Koran Weston, a fishkeeper from British Columbia, Canada, who has three freshwater community tanks: a 75 gallon, a 25 gallon, and a 10 gallon.
One day she got a hankering for a paradise fish. So she picked one that looked plump and healthy and added it to her 10-gallon tank.
Everything went fine for about a month—until the day that Weston noticed a red worm protruding from the vent of that plump, healthy-looking paradise fish. It was a camallanus worm, a nasty and contagious nematode that lives in the intestines of fish. It hadn’t been evident when she bought the fish, probably because there are several stages to the parasite’s lifecycle, and only the last one is visible to the naked eye. But soon it was wreaking havoc in all of her tanks. By the time the outbreak was under control three months later, she said, she’d spent some $200 on medication and lost dozens of fish, including her three beloved angelfish.
“Now I quarantine all fish for six weeks. No exceptions,” said Weston, who has a 5-gallon tank specifically for that purpose.
That’s music to the ears of Dr. Tim Miller-Morgan, an aquatic veterinarian who runs the ornamental fish health program of the Oregon Extension Sea Grant. “I’m constantly ranting about quarantine,” Miller-Morgan said. “It’s very underutilized, and yet it’s just essential.”
He explained that even healthy fish carry some pathogens; the reason they don’t get sick is because their immune systems are able to keep them in check. But when fish are placed under stress—as they are when they’re bounced from fish farm to wholesaler to retailer to a hobbyist’s tank—their resistance often drops, and pathogens can gain the upper hand.
And that’s where quarantine starts to get complicated. If every pathogen has its own life cycle, and the life cycle is often dependent on water conditions such as temperature, then how do you know how long of a quarantine is long enough? Is two weeks adequate, as some fishkeepers insist? Or three weeks? A month? Six weeks?
“There is little scientific evidence on what is the ‘ideal’ period,” admits Dr. Edward Noga, author of the textbook Fish Disease: Diagnosis and Treatment (Blackwell Publishing, 2000) and a professor of aquatic medicine at North Carolina State University’s veterinary college. “In general, a three- to four-week quarantine period is considered good, but [it] depends upon the particular pathogens that pose a risk to the population.”
Miller-Morgan said he knows some koi hobbyists who quarantine a new fish for a full year before adding it to a pond with established stock—“They don’t feel comfortable until they put it through a year of temperature fluctuations,” he explained—but in general he thinks a month is a reasonable amount of time to isolate new arrivals.
“Quarantine isn’t just to prevent disease from getting into the system,” he said. “It also lets the fish acclimate to new surroundings, a new system, new food. It gives them a chance to settle down and gives their immune system a chance to recuperate [from the stress of transport].”
And by the way, while most of us tend to think the point of quarantine is to protect our established stock, the reverse can also be true. The fish in your tank are used to certain pathogens that are already there, and have resistance to them, but a new fish added to that tank might not, Miller-Morgan explained. By isolating it, then adding small quantities of water from the established tank to the quarantine tank over a period of several months, you’ll give the new fish time the opportunity to build up resistance to any pathogens that might be present in that water.
But that’s not something most home aquarists should be doing for several reasons, and Miller-Morgan and Noga agree. First, both pointed out that professionals usually use medications based on an in-depth knowledge of both the species they’re dealing with and the kind of pathogens that species is prone to; they also understand the impact of medications on both organisms. Home aquarists, however, rarely have that kind of knowledge. In addition, adding medications to tank water is in itself a stressor to fish because it changes the concentration of dissolved solids in the water, which in turn affects the fish’s osmoregulatory processes.
And lastly, said Miller-Morgan, treating for diseases the fish may not have can ultimately lead to medication-resistant pathogens, which can create a much bigger problem down the line.
The only “problem” that has to be addressed with any tank that isn’t in constant use is how to keep the biofilter going. Some people keep a few fish in them, transferring them to their main tank when the quarantine tank is needed for new arrivals. You can also keep the biofilters running in a fish-free quarantine tank by adding small amounts of ammonia.
Personally, I keep my quarantine tanks empty between use; when I need them, I instant-cycle them by pulling filter pads from my established tanks and putting them into the quarantine-tank filters. (Alternatively, you can keep an extra box filter running in an established tank, ready to move to a quarantine tank when needed.)
If you need to sterilize a quarantine tank, Miller-Morgan says that bleach, at a concentration of 200 ppm (or 200 mg/liter of water), will do a great job. However, he cautions, organics do cause bleach to break down, so make sure you rinse everything thoroughly before using the bleach, or it won’t be as effective.
------------------------------------------------------------------------------------------------------------------
Now for my additional 2 cents:
I have looked at many disease books and there are parasites that while uncommon in the trade, do exist in the fish where the average life cycle is 90-100 days so for me, unless I am keeping the new fish by themselves forever, I quarantine new fish for 3-4 months. Things have changed over time so I no longer immediately medicate fish unless they are showing signs of disease. Exceptions to this are fish that are known to carry internal worms. These are dewormed no matter what. Other than that, since many farms now raise their fish in medicated water or send the fish in medicated water and many wild fish exporters medicate their fish before shipping, I don't expose new fish to any medicines unless and until they show signs of disease and then treat accordingly. The rest of the time is for the fish to get used to my schedules for feeding, water changes, lighting and just settling down.
Hope this helps.
But here we go The oxford dictionary defines quarantine the following way:
noun
1. a state, period, or place of isolation in which people or animals that may have been exposed to infectious disease are placed.
"horses entering the country must stay in quarantine longer"
verb
1. place (a person or animal) in quarantine in order to prevent the spread of an infectious disease.
"I quarantine all new fish for one month"
From a TFH article:
Why Quarantine a New Fish?
Judging from discussions I’ve had with other fishkeepers and debates I’ve seen on Internet fish sites, many hobbyists view quarantining new fish the way they do eating right. They know it’s something they should do, but, all too often, don’t.For some, it’s because they’re too impatient to wait out a quarantine period; they want that new fish in their tank now! For others, it’s an unwillingness to invest money and time in a tank they’re not going to use regularly. Some hobbyists seem to think the concept of quarantine is overblown; a disease outbreak, they believe, is something that happens to other people’s tanks, never their own. And of course there’s the unexpected acquisition—the fish that, say, your nephew wins at the fair, or the species we’ve been searching for that suddenly appears in our local fish shop. If we don’t buy it now, we rationalize, who knows when we’ll find it again—and, besides, it looks healthy. So why not take our chances?
To answer that question, here’s a horror story courtesy of Koran Weston, a fishkeeper from British Columbia, Canada, who has three freshwater community tanks: a 75 gallon, a 25 gallon, and a 10 gallon.
One day she got a hankering for a paradise fish. So she picked one that looked plump and healthy and added it to her 10-gallon tank.
Everything went fine for about a month—until the day that Weston noticed a red worm protruding from the vent of that plump, healthy-looking paradise fish. It was a camallanus worm, a nasty and contagious nematode that lives in the intestines of fish. It hadn’t been evident when she bought the fish, probably because there are several stages to the parasite’s lifecycle, and only the last one is visible to the naked eye. But soon it was wreaking havoc in all of her tanks. By the time the outbreak was under control three months later, she said, she’d spent some $200 on medication and lost dozens of fish, including her three beloved angelfish.
“Now I quarantine all fish for six weeks. No exceptions,” said Weston, who has a 5-gallon tank specifically for that purpose.
That’s music to the ears of Dr. Tim Miller-Morgan, an aquatic veterinarian who runs the ornamental fish health program of the Oregon Extension Sea Grant. “I’m constantly ranting about quarantine,” Miller-Morgan said. “It’s very underutilized, and yet it’s just essential.”
He explained that even healthy fish carry some pathogens; the reason they don’t get sick is because their immune systems are able to keep them in check. But when fish are placed under stress—as they are when they’re bounced from fish farm to wholesaler to retailer to a hobbyist’s tank—their resistance often drops, and pathogens can gain the upper hand.
How Long Is Long Enough?
How long it takes for this to happen, though, can depend on a number of factors, including the species of fish, the pathogen, and the water conditions both are living in. For instance, at temperature of 75° to 79°F, the life cycle of the parasite that causes ich is about 48 hours, while at 60°F, it can take nearly a week to complete.And that’s where quarantine starts to get complicated. If every pathogen has its own life cycle, and the life cycle is often dependent on water conditions such as temperature, then how do you know how long of a quarantine is long enough? Is two weeks adequate, as some fishkeepers insist? Or three weeks? A month? Six weeks?
“There is little scientific evidence on what is the ‘ideal’ period,” admits Dr. Edward Noga, author of the textbook Fish Disease: Diagnosis and Treatment (Blackwell Publishing, 2000) and a professor of aquatic medicine at North Carolina State University’s veterinary college. “In general, a three- to four-week quarantine period is considered good, but [it] depends upon the particular pathogens that pose a risk to the population.”
Miller-Morgan said he knows some koi hobbyists who quarantine a new fish for a full year before adding it to a pond with established stock—“They don’t feel comfortable until they put it through a year of temperature fluctuations,” he explained—but in general he thinks a month is a reasonable amount of time to isolate new arrivals.
“Quarantine isn’t just to prevent disease from getting into the system,” he said. “It also lets the fish acclimate to new surroundings, a new system, new food. It gives them a chance to settle down and gives their immune system a chance to recuperate [from the stress of transport].”
And by the way, while most of us tend to think the point of quarantine is to protect our established stock, the reverse can also be true. The fish in your tank are used to certain pathogens that are already there, and have resistance to them, but a new fish added to that tank might not, Miller-Morgan explained. By isolating it, then adding small quantities of water from the established tank to the quarantine tank over a period of several months, you’ll give the new fish time the opportunity to build up resistance to any pathogens that might be present in that water.
Is an Ounce of Prevention Worth a Pound of Cure?
Many of the professional aquarists I’ve talked to over the years go a step further, routinely medicating quarantined fish for a host of diseases, even if there’s no evidence those diseases are present. Some also give new freshwater fish a salt dip, and new marine fish a freshwater dip, to kill off parasites before placing them in quarantine.But that’s not something most home aquarists should be doing for several reasons, and Miller-Morgan and Noga agree. First, both pointed out that professionals usually use medications based on an in-depth knowledge of both the species they’re dealing with and the kind of pathogens that species is prone to; they also understand the impact of medications on both organisms. Home aquarists, however, rarely have that kind of knowledge. In addition, adding medications to tank water is in itself a stressor to fish because it changes the concentration of dissolved solids in the water, which in turn affects the fish’s osmoregulatory processes.
And lastly, said Miller-Morgan, treating for diseases the fish may not have can ultimately lead to medication-resistant pathogens, which can create a much bigger problem down the line.
Quarantine Basics
So what would a good quarantine system look like? The size of the tank will vary according to the sorts of fish you keep—larger or fast-swimming fish, for instance, require larger quarantine tanks than smaller, quieter fish. But beyond that, simpler is better; keep the lighting low—it keeps fish calmer—and make sure that anything you put into the tank is easily sterilized. That means opting for things like plastic plants and PVC pipe (added not to make the tank look beautiful, but to make the fish feel secure) over real or silk plants. “And nothing porous, like lava rock, because pathogens can get into the pores,” Miller-Morgan said. He also recommends skipping the substrate, since a barebottom tank is easier to keep clean and also to sterilize later. And, he adds, make sure that any nets and siphons used in a quarantine system are kept separate; using them in an established tank is a good way to spread pathogens.The only “problem” that has to be addressed with any tank that isn’t in constant use is how to keep the biofilter going. Some people keep a few fish in them, transferring them to their main tank when the quarantine tank is needed for new arrivals. You can also keep the biofilters running in a fish-free quarantine tank by adding small amounts of ammonia.
Personally, I keep my quarantine tanks empty between use; when I need them, I instant-cycle them by pulling filter pads from my established tanks and putting them into the quarantine-tank filters. (Alternatively, you can keep an extra box filter running in an established tank, ready to move to a quarantine tank when needed.)
If you need to sterilize a quarantine tank, Miller-Morgan says that bleach, at a concentration of 200 ppm (or 200 mg/liter of water), will do a great job. However, he cautions, organics do cause bleach to break down, so make sure you rinse everything thoroughly before using the bleach, or it won’t be as effective.
------------------------------------------------------------------------------------------------------------------
Now for my additional 2 cents:
I have looked at many disease books and there are parasites that while uncommon in the trade, do exist in the fish where the average life cycle is 90-100 days so for me, unless I am keeping the new fish by themselves forever, I quarantine new fish for 3-4 months. Things have changed over time so I no longer immediately medicate fish unless they are showing signs of disease. Exceptions to this are fish that are known to carry internal worms. These are dewormed no matter what. Other than that, since many farms now raise their fish in medicated water or send the fish in medicated water and many wild fish exporters medicate their fish before shipping, I don't expose new fish to any medicines unless and until they show signs of disease and then treat accordingly. The rest of the time is for the fish to get used to my schedules for feeding, water changes, lighting and just settling down.
Hope this helps.
Last edited:
I just read that very same article. Yes your response was very helpful because it is in 100% alignment with my thinking. The disagreement with the breeder is he defines quarantine to mean the use of several drugs. I have never done this. I have never brought a fish into my house that I knew to be ill or suspected was.
Andy Sager
Aquarium Advice Addict
But there are many pathogens inside the fish that unless the fish is stressed, don't show externally so you are always playing Russian Roulette if you don't quarantine. And now with the farmed fish and wild fish, the pathogens are different so it's recommended to not mix wild caught fish with farmed fish. For example: Yes the Ich parasite looks the same but there is no guarantee that the same medicine or same dosage will work on both types of fish.
The hobby has changed and so needs the hobbyist to do so. 
Where I differ from the article is that I usually use an established tank for quarantine since the fish is in there for months but will remove the fish to a bare bottom "Hospital tank" for medicating if necessary. I know many people medicate in their QTs but I don't because most of the meds I would use will suppress or kill off the biological filter so that just creates more problems or issues. A Hospital tank can be set up in minutes, broken down in minutes and can help show things like dead worms or infected poo on the bare bottom.
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Everything you say makes sense to me.
But has raised some concerns about new fish that arrived today, Rio Nanay. I would have preferred US domestic bred, but cannot find them, so went with an importer. Two fish are wild caught and two were tank bred in Europe. The wc are quite small. I have all in quarantine in yet another 14 gallon cube. They are very active and ate well on the first day. I fed lightly. All are in the same tank. I suppose you would recommend QT’ing such fish longer than usual? I have never prophylactically medicated any asymptomatic fish. And all of my fish have been symptom-free so far as I can determine.
But has raised some concerns about new fish that arrived today, Rio Nanay. I would have preferred US domestic bred, but cannot find them, so went with an importer. Two fish are wild caught and two were tank bred in Europe. The wc are quite small. I have all in quarantine in yet another 14 gallon cube. They are very active and ate well on the first day. I fed lightly. All are in the same tank. I suppose you would recommend QT’ing such fish longer than usual? I have never prophylactically medicated any asymptomatic fish. And all of my fish have been symptom-free so far as I can determine.
Andy Sager
Aquarium Advice Addict
I would recommend QTing them separately for the reasons I explained about the pathogens being different. I also looked up the 14 gallon cube tank and quite frankly, IMO it's too small for med to large Angels but fine for a small amount of smaller angels. A standard 10 gallon tank would be better for the smalls since it gives more length for the fish to disperse if they wanted to. Med standard Angels can be done in a 20 long for 3-6 while the 20 high is fine for a pair. Large standard Angelfish should be in at least a 36" long x 16" high tank depending on the amount of fish. Veiltails should be in taller tanks so we are talking the 29/ 55/ 60 tall tanks.
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