Why a fallow period will sometimes fail

Humblefish

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We've all seen claims of ich, velvet, etc. returning after a 76 day fallow period. (For anyone wondering what a fallow period means click here: https://www.reef2reef.com/threads/fallow-periods-going-fishless.190324/)

Oftentimes, a fallow period failure is due to human error: The sick fish weren't treated long enough or the treatment itself wasn't done properly, cross contamination via wet hands or equipment, aerosol transmission (more info). It is also possible that undiscovered strains of ich (and other diseases) exist; ones with a prolonged life cycle that exceeds what we know to be true from scientific research. However, there is also this possibility to consider:

Dormancy induced by a hypoxic environment in tomonts of Cryptocaryon irritans, a parasitic ciliate of marine teleosts
Abstract
We incubated tomonts of Cryptocaryon irritans in a hypoxic seawater environment (1.4–1.7 mg/L O2) (low dissolved oxygen; DO) and examined their development using a acetocarmine whole-mount staining method we developed for nuclear staining. They showed little development and stayed in the dormant phase in the hypoxic environment. When transferred into the hypoxic environment after incubation in an oxic environment (air-saturated, 8.7–8.9 mg/L O2) for 1–4 days, their development stopped in 1 day. However, when dormant tomonts generated in the hypoxic environment were transferred to the oxic environment, they resumed development and released theronts. These results indicate that tomonts can become dormant when exposed to a hypoxic environment, but can resume development when exposed to an oxic environment at any developmental stage. When exposed to the oxic environment, tomonts recovered from 1-month dormancy and released as many theronts as control tomonts constantly incubated in the oxic environment. The infectivity of theronts from the recovered tomonts was similar to the control tomonts. Thermoclines prevent oxygen-rich surface seawater from reaching the bottom of water column and create a hypoxic sea floor environment in summer; these thermoclines are broken down in autumn or after typhoons. The long-term viability of dormant tomonts in hypoxic environments may be a key factor in the autumn outbreaks of cryptocaryoniasis in floating net cages in temperate waters.
Highlights from the study:
  • This study demonstrates that tomonts of Cryptocaryon irritans become dormant in hypoxic environments.
  • Dormant tomonts resume development in oxic environments at any developmental stages.
  • We examined tomont viability following variable sequences of oxic and hypoxic conditions.
  • Dormancy in hypoxic environments may be key to the autumn outbreaks of cryptocaryoniasis in floating net cages in temperate waters.
So what does this mean for us and our fallow aquariums? Primarily, the study showed that an ich tomont (the "egg stage" which encysts to corals, inverts, rocks, etc.) can go dormant if the protomont crawls into a hypoxic (low oxygen) environment or anaerobic (no oxygen) region of your DT just before encysting. Examples of this include under your sand bed (especially a DSB), inside a non-porous rock, any "no flow" region of a canister or other aquarium filter. The study also demonstrated that once returned to an oxygen rich environment, these once dormant tomonts resumed their development and released theronts (free swimmers which seek out fish to infect.) How long can it take for a dormant tomont in a hypoxic environment to suddenly be exposed to an oxic (oxygen rich) environment? The world may never know?! :eek:

So what can you do to eliminate low oxygen areas of your DT during a fallow period?
  1. Take any canister or enclosed filters offline, and sterilize them with bleach. Without fish to foul the water, your DT will be fine with just rock/sand for filtration and good water circulation.
  2. Speaking of circulation, crank up those pumps for maximum flow & gas exchange throughout the aquarium. (Don't forget to add a pump down in the sump.)
  3. Blow out your rocks (using a powerhead) and vacuum the sand during water changes whilst going fallow. This will "stir things up" and provide free oxygen to those areas.
How can I setup my Display Tank to be "hypoxic proof" just in case I ever have to go fallow?
  1. Only use filtration with an open top (like a sump), and avoid canister filters and other filters which may contain anaerobic regions. If needed, take these offline if ever having to go fallow.
  2. Use just a light layer of sand; the deeper it is the more likely tomonts can get "trapped" down under there.
  3. Never have sand out of reach (i.e. under a rock) in case you need to vacuum it during a fallow period.
  4. Only use very porous rock which will allow plenty of flow (and oxygen) to pass through.
More information on Marine Ich (Cryptocaryon irritans) can be found here: https://www.reef2reef.com/threads/ich-cryptocaryon-irritans.191226/
 
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Brew12

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932165_1.jpg

We've all seen claims of ich, velvet, etc. returning after a 76 day fallow period. (For anyone wondering what a fallow period means click here: https://www.reef2reef.com/threads/fallow-periods-going-fishless.190324/)

Oftentimes, a fallow period failure is due to human error: The sick fish weren't treated long enough or the treatment itself wasn't done properly, cross contamination via wet hands or equipment, aerosol transmission (more info). It is also possible that undiscovered strains of ich (and other diseases) exist; ones with a prolonged life cycle that exceeds what we know to be true from scientific research. However, there is also this possibility to consider:

Dormancy induced by a hypoxic environment in tomonts of Cryptocaryon irritans, a parasitic ciliate of marine teleosts


Highlights from the study:
  • This study demonstrates that tomonts of Cryptocaryon irritans become dormant in hypoxic environments.
  • Dormant tomonts resume development in oxic environments at any developmental stages.
  • We examined tomont viability following variable sequences of oxic and hypoxic conditions.
  • Dormancy in hypoxic environments may be key to the autumn outbreaks of cryptocaryoniasis in floating net cages in temperate waters.
So what does this mean for us and our fallow aquariums? Primarily, the study showed that an ich tomont (the "egg stage" which encysts to corals, inverts, rocks, etc.) can go dormant if the protomont crawls into a hypoxic (low oxygen) environment or anaerobic (no oxygen) region of your DT just before encysting. Examples of this include under your sand bed (especially a DSB), inside a non-porous rock, any "no flow" region of a canister or other aquarium filter. The study also demonstrated that once returned to an oxygen rich environment, these once dormant tomonts resumed their development and released theronts (free swimmers which seek out fish to infect.) How long can it take for a dormant tomont in a hypoxic environment to suddenly be exposed to an oxic (oxygen rich) environment? The world may never know?! :eek:

So what can you do to eliminate low oxygen areas of your DT during a fallow period?
  1. Take any canister or enclosed filters offline, and sterilize them with bleach. Without fish to foul the water, your DT will be fine with just rock/sand for filtration and good water circulation.
  2. Speaking of circulation, crank up those pumps for maximum flow & gas exchange throughout the aquarium. (Don't forget to add a pump down in the sump.)
  3. Blow out your rocks (using a powerhead) and vacuum the sand during water changes whilst going fallow. This will "stir things up" and provide free oxygen to those areas.
How can I setup my Display Tank to be "hypoxic proof" just in case I ever have to go fallow?
  1. Only use filtration with an open top (like a sump), and avoid canister filters and other filters which may contain anaerobic regions. If needed, take these offline if ever having to go fallow.
  2. Use just a light layer of sand; the deeper it is the more likely tomonts can get "trapped" down under there.
  3. Never have sand out of reach (i.e. under a rock) in case you need to vacuum it during a fallow period.
  4. Only use very porous rock which will allow plenty of flow (and oxygen) to pass through.
More information on Marine Ich (Cryptocaryon irritans) can be found here: https://www.reef2reef.com/threads/ich-cryptocaryon-irritans.191226/
Ugh. It never gets any easier. :(

I do appreciate the work you put in to make sure we are informed.
 
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Brew12

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I'd ban you from this thread except for the fact you can unban yourself!
 

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Just when I was thinking about jumping on the QT train lol. I'm seriously considering just purchasing all captive bred fish at this point...
 
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Humblefish

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Just when I was thinking about jumping on the QT train lol. I'm seriously considering just purchasing all captive bred fish at this point...
I will say I don't think tomonts going dormant is a common occurrence. Maybe more the exception than the rule. And taking these simple steps will help counteract tomont dormancy if it does occur:
  1. Take any canister or enclosed filters offline, and sterilize them with bleach. Without fish to foul the water, your DT will be fine with just rock/sand for filtration and good water circulation.
  2. Speaking of circulation, crank up those pumps for maximum flow & gas exchange throughout the aquarium. (Don't forget to add a pump down in the sump.)
  3. Blow out your rocks (using a powerhead) and vacuum the sand during water changes whilst going fallow. This will "stir things up" and provide free oxygen to those areas.
 
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Humblefish

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Thanks for the great write up. Might indeed explain weird outbreaks of ich or especially velvet in tanks sometimes months after no fish additions ?
It's very possible that this study is the smoking gun and answer to that. However, I haven't found any similar studies regarding Amyloodinium (Velvet) tomonts being able to go dormant.
 

Brew12

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It's very possible that this study is the smoking gun and answer to that. However, I haven't found any similar studies regarding Amyloodinium (Velvet) tomonts being able to go dormant.
I think it is important to point out that Cryptocaryon Irritans is a Ciliate parasite where Velvet is a Dinoflagellate. Both are parasites but they are not similar enough to think they will behave similarly in regards to fallow periods.
 

Reefahholic

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This is why you never let ICH in your DT! :p

Thanks for the write up Humble! ;)

This is probably very unlikely, but good to know that this could potentially happen. Now hide this thread, because every newbie that cross-contaminates will now blame his failure on a hypoxic environment. :D
 

TheEngineer

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Very interesting! It’s a little scary, but also really helpful. Maybe we (or at least me) need to change how we think of fallow periods. Fallow periods aren’t periods of inactivity. They are active periods of cleaning and rejuvenating.
 

ScooterV

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cross contamination via wet hands or equipment
I bet I know who you thought of for that one!! Although, it's still unknown if I actually did contaminate other than frequently catching myself doing dumb, reflexive things. The two clowns are still doing great by the way, and inseparable :)
 

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Wowkuh

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I have a sump (slightly covered) should I fully uncover? Everything running as normal. Return pumps power heads skimmer etc.... Bare bottom tank. I should be good right? I'm about 2 weeks into fallow. All QT and other aquariums are appx 12' away.

@Humblefish
 

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