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Risk statistics on tropical disease transfers to a healthy tank

Mill.Shires

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o.k... I had a discussion with a store owner who told me fewer than 5% of his fish were ever infected, yet I contantly see "not for sale" "sick" notices on tanks (in lots of stores). A former fish store employee told me that so many fish were sick in the store he worked at that they routinely treated almost all fish on delivery. Another fish bench-bleacher employee told me even if a fish is sick with a bacteria (not parasite) infection, it is rare that the sick fish would transfer the bacteria to healthy fish in a healthy tank....so there is very little risk of infection from a store bought (sick) fish. He also said that is why many stores have central filtration systems instead of individual tanks --- because the risk of cross infection is very low. A claim that fish don't transfer disease between/to other varieties (such as a cardinal tetra infecting a yellow rainbow) seemed highly suspect to me.

I can't find any supporting science or statistic information about:

1. What % of fish in a store/received by a store are actually diseased or parasitized
2. What is the risk of a sick fish giving a different kind of fish a disease
3. What is the risk level of a purchased disease or parasite fish infecting a varied population in a healthy tank

Any owners or ichthiologists out there that can shed some light on this? I have been keeping fish for more than 25 years and have rarely had disease outbreaks in my tank. A store recently sold me some sick fish and more or less shrugged their shoulders --- even after they posted a "sick" sign on the tank of fish from which mine was purchased just 2 days prior to the posting (yes, 50% of the ones I bought died)....I can deal with that. What I am concerned about is the health of my other fish....and curiosity about more science behind the tropical fish industry and diseases. I know risk can vary from disease to disease, that sickness falls into 4 broad categories (bacterial infections, fungal infections, parasitic, or protozoan infections) ---- and also that some diseases are fairly common. So ruling out those rare or singly specific (such as only infect catfish) --- what are some broad, research/statistic backed general conclusions?
 

Byron

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The health and condition of the fish itself has a great deal to do with disease. Stress is the direct cause of 95% of all fish disease in aquaria. So avoiding and preventing stress, or keeping it as minimal as possible, goes a long way to avoiding disease. Take ich as an example. Why haven't all freshwater fish in nature died long before now from ich? Ich is present, it is not an aquarium phenomenon. And there is now belief that ich is present in most of our aquaria permanently. No other explanation can account for a sudden outbreak of ich if the heater fails and the tank chills when nothing new has gone into it for months.

I never used to quarantine new fish, and I did this for 20+ years; aside from a couple bouts of ich, nothing. Then about five years ago, I introduced 16 new tetras to my 115g tank, and then suddenly after one week fish began dying, half the new fish were dead almost overnight and my other species began dying at the rate of one or two fish every day. There were no external signs at all. A marine biologist suggested it was likely an internal protozoan, and on her advice metronidazole added to the food for two weeks cured whatever it was. Two years later, something similar happened, and from then on I have quarantined new fish. Protozoan have become much more prevalent. I have kept fish in quarantine for five weeks before something like this turned up in the fish. But I was glad it was only the new fish in the QT.

The source of the fish in stores plays a significant role in disease. I have found over the last years that wild caught fish rarely if ever have disease problems; all of the disease issues I have had have come in with commercially-raised fish, or fish from chain stores--I will absolutely never acquire any fish from Petland, PetSmart, or similar stores; it just isn't worth the risk, given my experiences. I am lucky to have a few independent stores close by, including a couple that direct import. The absence of any disease issues with their fish cannot just be coincidence.

You asked about the risk of a diseased fish spreading to other fish. This depends firstly upon the disease, secondly upon the health of the other fish. Remember, stress is 95% responsible for fish disease. But here we come to the important science: when we understand the aquatic environment and the unique physiology of fish, it is easy to see why.

The interaction between a fish and its aquatic environment is far greater than the interaction of any terrestrial animal with air/land, with the exception of amphibians. It is in fact perfectly unique. Fish live in water, and 80% of a fish is also water, and these are separated by nothing more than a simple membrane. The water in which a fish lives is being drawn into the fish via osmosis through every cell on the body, and in the gills. Thus, every substance and pathogen in the water is getting inside the fish, into the bloodstream and internal organs. This is significantly more direct than animals breathing air, and we know how easily some germs can be passed through air. Fish build up various immunities, which function very well--until stress occurs. Stress seriously compromises the immune system of fish by weakening it, just as it does in humans, only even more significantly. The immune system, as part of the homeostasis of a fish, keeps any problems under control. However, if there is an alteration in one or more of the environmental characteristics, there will likely be a shift in the balance to the detriment or benefit of either the fish or the pathogen. Environmental factors here refers primarily to water parameters--a fish's homeostasis is designed to only function well with a very specific set of environmental factors; but other environmental factors are also pertinent. If the environmental shift is against the fish, then stress will occur.

When we consider what a fish goes though from capture, transport, store tank conditions, netting, into a new environment--it is frankly amazing that any survive. Unfortunately, many do not.

Byron.
 
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Mill.Shires

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Thank you!
Are there any retail statistics on losses of fish in pet stores? Or transport between fish farm and store? I believe a lot of issues with aquarists, most whom are consciencious, reside in poor handling and facilities at retailers and farms. But I have no statistics to back that up. It would be interesting to know if 10% or 20% or 30% (horrors) of all live farmed tropical fish are "lost" to disease in fish stores. Like Byron, I have kept fish for decades and some evidence seems to point to it being more stressful to fish to quaranteen rather than getting them into the tank sooner. I, too, have rarely lost fish --- except on occasions after purchasing new fish. I wonder if protozans are more prevalent and responsible than "bacteria" which are often singled out as the cause of fish disease. The other day a fish store employee told me they routinely treat their tanks for ich --- the product he showed me was for bacterial diseases. He actually got angry at me when I pointed that out. :)
 

NickAu

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When we consider what a fish goes though from capture, transport, store tank conditions, netting, into a new environment--it is frankly amazing that any survive. Unfortunately, many do not.

 

Byron

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Thank you!
Are there any retail statistics on losses of fish in pet stores? Or transport between fish farm and store? I believe a lot of issues with aquarists, most whom are consciencious, reside in poor handling and facilities at retailers and farms. But I have no statistics to back that up. It would be interesting to know if 10% or 20% or 30% (horrors) of all live farmed tropical fish are "lost" to disease in fish stores. Like Byron, I have kept fish for decades and some evidence seems to point to it being more stressful to fish to quaranteen rather than getting them into the tank sooner. I, too, have rarely lost fish --- except on occasions after purchasing new fish. I wonder if protozans are more prevalent and responsible than "bacteria" which are often singled out as the cause of fish disease. The other day a fish store employee told me they routinely treat their tanks for ich --- the product he showed me was for bacterial diseases. He actually got angry at me when I pointed that out. :)
I have not come across numbers for losses, but then I am not in that branch of the hobby (retail) so it is of little interest from that perspective.

Just want to clarify something that seems to have come across contrary to what I meant...I do quarantine and I do strongly recommend it. My experience with disease over the last five years along with discussions with biologists would suggest there is much more significant health/disease issues in fish today, especially farm fish (commercial fish hatcheries/suppliers). Not quarantining is a serious risk. Twice I lost about 1/3 of my existing fish in a tank, that convinced me.

Protozoan can be internal or external, and without dissection after death by a microbiologist, impossible to identify. Bacteria is something I am less concerned about. But if I acquire say 20 new fish, and after 3-4 weeks in the QT they begin dying, the cause being protozoan or bacterial doesn't much matter. If this occurs in the main tank without a QT period, then obviously one has to ID the issue or treatment can be futile.

There is limited value to treating fish for something that "might" be present. All medications stress fish, and if this is only adding more stress while not actually doing anything beneficial, the fish are even more likely to become sick and die. I only treat for specific issues when i can be fairly certain of the issue, and if I then deem it to be contagious. I would sooner euthanize a fish that is obviously not going to make it, rather than subject all of them to some treatment when I have no idea what the issue is that is debilitating the lone fish. However, ich is so common that stores frequently do treat for this, and that I think is very wise.
 
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Mill.Shires

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:thanks: I do get the quarantine message, and sadly I didn't quarantine my recent purchase. I normally do, but it has been so long since I had sick fish or dead fish after a purchase, I took a short cut and now regretting it and feeling angry at myself more than at the ignorance of the store staff. So I was trying to figure out how high the risk actually is --- but given your post I guess I would say it is pretty clear quarantining is essential.

Oh...and pretty obvious those 3 day return/guarantees from stores are pretty silly if the issue doesn't show up for 3 or 4 weeks! Then they just blame the aquarist. :)
 

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