Marine Ich and Temperature

[HumbleFish]

I recently reexamined some of the literature I have on Marine Ich, paying closer attention to what it says about temperature and its effect on the parasite's known life cycle. As with most studies, precise conclusions can be somewhat ambiguous, but I wanted to share what I have learned and open a discussion regarding this topic.

The first article I reread was the 1997 Colorni and Burgess study, where it states: "œTheront excystment is very asynchronous, occurring between 3 and 72 days." This is the study which the infamous 72 day fallow period is based upon, and it has been suggested it took up to 72 days only because the original experimentation was done in cold water. Indeed, this excerpt from the article seems to support that:

The Australian trophonts stayed on the fish longer, tomonts took longer to excyst and the theronts were larger when fish were infected at 20C compared to 25C (Diggles and Lester, 1996a).

For the reader's reference, 20C=68F and 25C=77F.

However, later in the article (see red highlights below) it states that that the reason for the asynchronous excystment is "unclear". Wouldn't they just say the prolonged excystment (72 days) was due to cooler water temps if they were confident that was the case?

Even under identical incubation conditions tomonts vary considerably in the time required to form theronts (Nigrelli and Ruggieri, 1966; Colorni, 1992; Burgess and Matthews, 1994a; Diggles and Lester, 1996b). Thus, theront excystment is very asynchronous, occurring between 3 and 72 days and peaking at 6 ± 2 days (Colorni, 1992). This differs significantly from I. multifiliis, where the theront excystment takes only 18-24 h at 23C (Dickerson and Dawe, 1995).

The reason for asynchronous excystment is unclear. There is no relationship between the tomont size and excystment time (Nigrelli and Ruggieri, 1966; Colorni, 1992; Diggles and Lester, 1996a,b). In fact, a large and a small tomont may produce theronts at the same time, even though the smaller tomont undergoes fewer divisions. When tomites do not form until at least 2 weeks, a mass of endoplasm remains undifferentiated and fewer live theronts are produced (Colorni, 1992). Whatever the cause, asynchronous excystment prevents simultaneous exhaustion of all tomonts, facilitates theront dispersal in time and appears so advantageous to C. irritans that the phenomenon should be interpreted as a strategy for survival (Colorni, 1985).

I wouldn't think they'd label it a "œphenomenon" if the simple explanation was that cooler water temps were a contributing factor for asynchronous excystment. It could be because later on they discuss "œcold water intraspecific variants" which only adds to the confusion:

Cryptocaryon irritans was considered to be restricted to warmwater marine environments. However Diamant et al. (1991) found that C. irritans has a counterpart in the cooler waters of the eastern Mediterranean and Diggles and Lester (1996c) collected Cryptocaryon-infected fishes from Moreton Bay, Queensland, Australia, where the water temperature can fall to 15C. By comparing the rDNA sequences of isolates from Australia, Israel and the USA, Diggles and Adlard (1997) confirmed the existence of warm water and cold water intraspecific variants of C. irritans.

Can a cold water variant infect a reef fish typically found in warmer waters? And vice versa? With regards to temperature, the study was actually more focused on its correlation to trophont/tomont/theront size:



The next "œarticle" I reread was a 332 page PDF, written by Peter Burgess in 1992, where he conducted a series of experiments to partially fulfill the requirements for his PhD. Some of the information contained therein is now considered outdated/obsolete, but it still lays the groundwork for most of what we know about the parasite. One such example of possible outdated info is this excerpt:

The distribution of C.irritans in the wild appears to be limited by temperature. Under aquarium conditions, C.irritans has not been shown to develop or transmit below 19C to 20C (Wilkie and Gordin, 1969; Cheung et al., 1979) or above 30C (Cheung et al., 1979). Based on this information, it is considered that C.irritans is restricted to warmwater marine environments, although recent observations by Diamant et al. (1991) suggest that C.irritans may have a counterpart existing in the cooler waters of the eastern Mediterranean. This assumption was based on reports of disease outbreaks caused by a Cryptocaryon- like ciliate which was believed to have originated from cultured fish stocks from Cyprus and northern Israel.

I know from reading more recent studies that it has been proven ich can go dormant (for up to 6 months, I believe) if temp is lowered, but then become infectious again once the temp is returned to normal. I do not know if the same applies if you were to raise aquarium temperature above 30C/86F. According to "œTable 2" from this source, it would take 40C/104F for 1 hour to disinfect SW ich from your aquarium: https://edis.ifas.ufl.edu/fa164. However, I would think 104F would eradicate even nitrifying bacteria thus "œuncycling" your tank. I don't believe most fish/corals/inverts could handle > 86F (they would ALL need to be removed beforehand), but I do believe bacteria could survive that. The question is how long would you need to keep the aquarium > 86F to eradicate ich from it?

Next up is this table which outlines the development of C.irritans trophonts at different temperatures:



However, I found nothing above to be useful for our purposes since most of the animals we keep couldn't survive in 17C/62.6F water.

Finally, the study had this to say regarding temperature and immune response to SW ich:

The kinetics of the antibody response to C.irritans is likely to be influenced by temperature, within the physiological limits of the host, as is well recognised for teleosts antibody responses in general (Rijkers et al., 1981; Rijkers, 1982; Bly and Clem, 1992). The timing may also vary according to the host species, and there is some evidence to support this (Rijkers, 1982). Sailendri and Muthukkaruppan (1975), using Tilapia mossambica, have shown that under tropical conditions (30°C) a primary antibody response can be elicited within as short a period as five days after exposure to antigen. Although the species of mullet used here has a southerly distribution, extending to the Mediterranean (Lythgoe and Lythgoe, 1971), the speed of its immune response might not be representative of tropical marine fish species normally encountered by C.irritans. The delay in antibody response, recorded here, following intraperitoneal injection could also be attributed to temperature, as mullet immunized by this route were maintained at 5-10°C lower than those exposed to C.irritans by natural infection.

Two other articles I have not read on the subject, so I will just copy & paste their abstracts below:

Studies on cryptocaryoniasis in marine fish: effect of temperature and salinity on the reproductive cycle of Cryptocaryon irritans - Journal of Fish Diseases Volume 2, Issue 2, pages 93"“97, March 1979

Abstract. Trophonts of Cryptocaryon irritans Brown from infected three-spot damselfish, Dascyllus trimaculatus Ruppell, were kept at temperatures ranging from 7 to 37°C to observe encystment and development of the tomites. At 30, 25 and 20°C, the percentage of trophonts that had encysted in 16 h were 70, 77 and 64% respectively; at 37°C, 44% encysted and at 7°C only 10% had encysted.

The optimum temperature for excystment was 30°C; 50% excysted in 5 days and 100% in 7 days. At 25°C, 60% of the tomites started to excyst on the eighth day, and 70% on the ninth day. At 20°C, 10% started to excyst on the ninth day, reaching 40% on the tenth day. No excystment occurred at 37 and 7°C.

Newly encysted tomonts were placed in various dilutions of sea water (31 %0) and kept at temperatures ranging from 7 to 37°C. Low salinities, i.e. 16%0 and lower caused tomonts to rupture. At 37, 20 and 7°C, 35% of the tomonts started to rupture immediately in 50% sea water, while at 30 and 25 C, 30% of the tomonts ruptured in 25% seawater. However, none of the cysts developed normally at these dilutions. The percentage rupturing increased with decreasing salinity.

Influence of Temperature and Host Species on the Development of Cryptocaryon irritans
B. K. Diggles and R. J. G. Lester
The Journal of Parasitology
Vol. 82, No. 1 (Feb., 1996), pp. 45-51

Abstract. The course of infection of the parasitic ciliate Cryptocaryon irritans was followed on Lates calcarifer and Macquaria novemaculeata at 20 and 25 C. The parasite was originally isolated from locally caught Acanthopagrus australis. At 20 C trophonts stayed on the fish longer, tomonts took longer to excyst, and the resulting theronts were larger than at 25 C. On L. calcarifer at 20 C, trophonts grew slowly at first but eventually became significantly larger (mean tomont diameter 466 x 400 µm) than at 25 C (mean diameter 373 x 320 µm). On M. novemaculeata, trophonts never grew as large as on L. calcarifer and at 20 C they grew poorly. The number of theronts produced per tomont was directly related to the size of the tomont but was not influenced by incubation temperature. The tomont incubation period was not related to the diameter of the tomont but was significantly influenced by the host origin of the tomont. Theront size was also significantly affected by the host origin of the tomont but not the diameter of the tomont. These results show that C. irritans exhibits variability in morphometrics on different hosts and under different temperature conditions. This variability needs to be taken into account if utilizing morphometric data for separating strains of C. irritans.

Conclusions: Some of the information above is unusable for our purposes, as many of the animals we keep will not live in the experimental temperatures shown to have a negative impact on ich's life cycle. Although, those with cold water SW tanks battling ich might find it useful. The main thing I was looking for was whether or not the recommended 72 day fallow period is greatly exaggerated due to experimentation being conducted at cooler water temps. And while I admit there is some evidence to support it is, I also believe there are other variables in play which determines how long it can take for all the theronts to be released (or rupture) from their respective tomonts. I also cannot discount the numerous anecdotal accounts of 72 day fallow failures, or chalk every single one of them up to cross contamination or some other mental error on the part of the hobbyist. In short, we probably don't know as much about ich as we think we do.

I do think, however, that it would be prudent to monitor aquarium temp while going fallow. You probably want it to be at least 77F, and it is possible that running it at 80-82F will speed up ich's life cycle and increase your chances of having a successful fallow period. At the very least, it does no harm as most corals/inverts handle 80-82F just fine (except for possibly certain SPS.)

Whether you decide to go fallow for the entire 72 days (actually 76 if you factor in more than just the tomont stage), or roll the dice on a shorter duration is entirely up to you. For those who opt for the latter, Table 1 (below) provides some useful info taken from here: http://atj.net.au/marineaquaria/marineich.html



It shows lengths of stages of C. irritans from various studies before the 1997 Colorni and Burgess Study. In these listed studies, 35 days was the longest time it took for theront release (Burgess and Matthews, 1994a). So, 45 days fallow should be sufficient for most garden variety strains of ich so long as temp is 77F or greater during the entire fallow period.

One last thing I wanted to mention is something I said previously - about ich going dormant in lower temps and then becoming infectious again once the temp is returned to normal. That information is quoted below and was extracted from here: https://edis.ifas.ufl.edu/fa164

Temperatures for optimal growth of most strains of Cryptocaryon appear to be about 23"“30°C (73.4"“86°F) (Dickerson 2006; Yoshinaga 2001), although active infections at 15°C (59°F) have been documented (Diggles and Lester 1996). Encysted stages, off the host (tomonts), were also observed to survive for 2"“4 weeks under experimental hypoxic conditions (24% oxygen saturation); these released free-swimming infective stages (theronts) 10"“11 days after excystment (Yoshinaga 2001).

A more recent study demonstrated that two life stages of one strain of Cryptocaryon (trophonts, i.e., the feeding stage during which the parasite can be found on the fish, and tomonts) survived dormant for 4"“5 months at 12°C (53.6°F), and, after the water temperature increased to 27°C (80.6°F), developed and infected fish (Dan et al. 2009).

So let's now begin a lively discussion, debate, more info presented, etc. on Marine Ich and Temperature!

 

[ThRoewer]

You got a link to that 1997 Colorni and Burgess study, full text ideally? I've been searching for it but couldn't find it so far.

 

[microlady]

This is awesome. I've often wondered if a fallow period shorter than 72 days would be fine. Bob Fenner usually suggests that a month might work, but that two is better. Maybe most strains would die out after 35 days at 81 degrees. Hmmmm, I could always place my yellow tang back into the tank at the 40 day mark. He would be the easiest one to remove if it didn't work . . .

 

[microlady]

Or it might be better to add display water to the quarantine tank, and possibly a little sand. Then the fish would break out in the quarantine and not the display.

 

[Deinonych]

Or it might be better to add display water to the quarantine tank, and possibly a little sand. Then the fish would break out in the quarantine and not the display.

I think that would be a more prudent course of action. Kind of a "canary in a coal mine" approach. Even better to do it with a single fish isolated in a QT.

 

[ThRoewer]

Or it might be better to add display water to the quarantine tank, and possibly a little sand. Then the fish would break out in the quarantine and not the display.

I think that would be a more prudent course of action. Kind of a "canary in a coal mine" approach. Even better to do it with a single fish isolated in a QT.

That wouldn't be an reliable approach. The issue is that excystment and release of the threonts always happens in the dark (=night). If you take the water out in the morning or even in the evening, many if not all threonts may have been eaten or been removes (skimmer).
If a fish is in the tank the threonts will find and infect it quickly, but only an hour after excystment, corals, filter feeders and other predators may have eliminated all threonts.

The only way to have a somewhat reliable canary test would require to put a guaranteed non-immune fish into the tank and keep it there over night (in a cage for easy removal). The next day you would remove him (and replace him with the next "canary") to an observation tank to see if he will get sick.

Each test fish could only be used once and would ideally need to be held in isolation (that way you know when the last cyst popped).

I think this would be out of the scope for an average aquarist.

 

[HumbleFish]

Perfect canary fish = freshwater black molly. Once converted over, it would have no immunity to any saltwater diseases and ich/velvet/brook would show up easily on it. They are slow swimming (so easy to catch), but I know public aquariums will put them in an acclimation box for a week or so to see if a fallow period has been successful.

But it has to be a freshwater black molly, that you yourself convert over to full SW. One that has already been converted over (by a LFS) could actually introduce a disease into your DT the same as any other SW fish.

 

[coolxborg]

Perfect canary fish = freshwater black molly. Once converted over, it would have no immunity to any saltwater diseases and ich/velvet/brook would show up easily on it. They are slow swimming (so easy to catch), but I know public aquariums will put them in an acclimation box for a week or so to see if a fallow period has been successful.

But it has to be a freshwater black molly, that you yourself convert over to full SW. One that has already been converted over (by a LFS) could actually introduce a disease into your DT the same as any other SW fish.

Yes, this is exactly what Im going to do. DT is currently fallow.

If the fallow period works, then the molly(ies) will be part of clean up crew.

 

[Deinonych]

The only way to have a somewhat reliable canary test would require to put a guaranteed non-immune fish into the tank and keep it there over night (in a cage for easy removal). The next day you would remove him (and replace him with the next "canary") to an observation tank to see if he will get sick.

Yeah, I guess that would make better sense. Place the "canary" in the DT, expose it to the (potential) parasite, then place in observation so the parasite doesn't continue its life cycle in the DT if present.

 

[ThRoewer]

Perfect canary fish = freshwater black molly. Once converted over, it would have no immunity to any saltwater diseases and ich/velvet/brook would show up easily on it. They are slow swimming (so easy to catch), but I know public aquariums will put them in an acclimation box for a week or so to see if a fallow period has been successful.

But it has to be a freshwater black molly, that you yourself convert over to full SW. One that has already been converted over (by a LFS) could actually introduce a disease into your DT the same as any other SW fish.

That's pretty much what I had in mind.
Black Mollies are ideal because you see ich easily on them.

 

[ginpang]

Thanks for posting. Interesting read.

 

[microlady]

Good ideas, people! So do you suggest keeping the Molly in a breeder box for easy removal? How long should you leave it in to be sure you are in the clear?

 

[HumbleFish]

Good ideas, people! So do you suggest keeping the Molly in a breeder box for easy removal? How long should you leave it in to be sure you are in the clear?

I would say at least a couple of weeks to be sure. And personally, I wouldn't put them in a breeder box unless the flow in your DT is too much for them. When you're ready to take them out, just put some nori in a clip near the top of the tank. They swim very slow and are easy to catch with a net.

 

[ThRoewer]

Good ideas, people! So do you suggest keeping the Molly in a breeder box for easy removal? How long should you leave it in to be sure you are in the clear?

I would use a breeder box.

The time in the tank should be 2 days at the most, or you need to restart the clock on your fallow period.

Keep in mind, you want to see if still theronts hatch, but not release new tomonts into the tank.

The diagnosis whether the canary fish got infected or not has to be made in the observation tank.

 

[microlady]

I would use a breeder box.

The time in the tank should be 2 days at the most, or you need to restart the clock on your fallow period.

Keep in mind, you want to see if still theronts hatch, but not release new tomonts into the tank.

The diagnosis whether the canary fish got infected or not has to be made in the observation tank.

Ok I might try this around the 7 week mark. I want to go fallow at least 6 weeks just in case velvet or Brook was involved.

 

[coolxborg]

I would use a breeder box.

The time in the tank should be 2 days at the most, or you need to restart the clock on your fallow period.

Keep in mind, you want to see if still theronts hatch, but not release new tomonts into the tank.

The diagnosis whether the canary fish got infected or not has to be made in the observation tank.

Thanks for this. I didnt think through my plan enough. It would be painful to start the fallow period again.

Would two days be enough? How long would we need to observe the canary fish after the 2 day period?

Sorry @humblefish. We kinda diverted from the subject of your thread.

 

[HumbleFish]

Thanks for this. I didnt think through my plan enough. It would be painful to start the fallow period again.

Would two days be enough? How long would we need to observe the canary fish after the 2 day period?

Sorry @humblefish. We kinda diverted from the subject of your thread.

No worries, it's all good. FWIW; 2 days would be long enough if all you were testing for were active theronts in the water. However, if you were waiting to see if some tomonts had not yet ruptured, a longer "canary period" would be required.

 

[ThRoewer]

Thanks for this. I didnt think through my plan enough. It would be painful to start the fallow period again.

Would two days be enough? How long would we need to observe the canary fish after the 2 day period?

...

2 days per canary fish, never longer!

If you want to do this you will need to get a good number of mollies. Each can only be used once and the exposure time in the tank can't be any longer than 2 days.

After their 2 day exposure in the DT they need to be observed for at least 2 weeks, ideally each in its own isolated tank (one gallon tanks should do). Only this way you can tell when the last one was infected.

If you lump them together you will just know that there is still ich in the DT, but don't know when the infection occurred. If it is just to check after the 11 week fallow period if the tank is clean then this should be fine.

The minimum period I would do this is 2 weeks = 7 mollies. If you want a higher confidence level go 4 weeks with 14 mollies. In that case I would recommend to do 2 to 4 observation tanks (one for two weeks or one for each), so that you have at least some idea when the last (if any) infection occurred.

It is also very important that the mollies used for this come from freshwater and were never in saltwater before. Best is to use young ones.
To adapt them to saltwater use only sterile saltwater (freshly mixed or boiled). It's also best to keep the clean (unexposed) fish in an entirely different room to avoid any chance of cross contamination.

 

[HumbleFish]

Just wanted to share a little follow-up to this thread.....

I reached out to Dr. Colorni, who co-authored the article which established the "72 day rule" for ich. Here is my email to him:

Dear Sir,

I am writing to you regarding this article you co-authored back in 1997: http://link.springer.com/article/10.1023/A:1018360323287

The part I have a question about is quoted below:

Even under identical incubation conditions tomonts vary considerably in the time required to form theronts (Nigrelli and Ruggieri, 1966; Colorni, 1992; Burgess and Matthews, 1994a; Diggles and Lester, 1996b). Thus, theront excystment is very asynchronous, occurring between 3 and 72 days and peaking at 6 ± 2 days (Colorni, 1992). This differs significantly from I. multifiliis, where the theront excystment takes only 18-24 h at 23C (Dickerson and Dawe, 1995).

The reason for asynchronous excystment is unclear. There is no relationship between the tomont size and excystment time (Nigrelli and Ruggieri, 1966; Colorni, 1992; Diggles and Lester, 1996a,b). In fact, a large and a small tomont may produce theronts at the same time, even though the smaller tomont undergoes fewer divisions. When tomites do not form until at least 2 weeks, a mass of endoplasm remains undifferentiated and fewer live theronts are produced (Colorni, 1992). Whatever the cause, asynchronous excystment prevents simultaneous exhaustion of all tomonts, facilitates theront dispersal in time and appears so advantageous to C. irritans that the phenomenon should be interpreted as a strategy for survival (Colorni, 1985).

And also this section:

The Australian trophonts stayed on the fish longer, tomonts took longer to excyst and the theronts were larger when fish were infected at 20C compared to 25C (Diggles and Lester, 1996a).

As I am sure you are aware, 72 days is an unusually long time to take for theronts to excyst from tomonts. In most other studies I've seen, 35 days was the longest time it took for theront release. Do you think the cooler 20C water temperature was directly responsible for the prolonged excystment period?

I am needing this information to help determine what might be the proper fallow period if a marine aquarium was infected with Cryptocaryon. I thought less than 72 days might be sufficient if the aquarium was being maintained at a more "reef-like temperature" of 25C, for example. Your expertise in this matter would be greatly appreciated.

Kind regards,
Bobby

Dr. Colorni graciously took the time to respond to me and his reply can be found below:

Dear Bobby,

Thank you for your (continuous) interest in my work.

Undoubtedly, low temperature slows down Cryptocaryon's metabolism and thus lengthens its life cycle. Indeed 72 days were an exceptional period, but it occurred with the aid of antibiotics in a sterile flask. In nature (and in an aquarium), over more than two months, I would expect bacteria to "œgnaw" on the tomont and eventually damage it.

In conclusion, a combination of "œreef-like" temperature and non-aseptic conditions should make a quarantine period "œless than 72 days". How long such period should be presumed to be safe remains a difficult question. The bug has millions of years of evolution on its side...!

Sorry I can't give you a more clear-cut answer.

Keep up the good work,

Angelo

**********************************************************************

Angelo Colorni, Ph.D., Senior Scientist
Retired ! Former Head, Dept. of Pathobiology

National Center for Mariculture
Israel Oceanographic and Limnological Research

- P.O.Box 1212, Eilat 88112, Israel

Research Website: www.ocean.org.il

**********************************************************************

Life is a whim of several billion cells to be you for a while.

 

[HumbleFish]

Without a clear-cut answer, I feel it is advisable to continue to go fallow for 72 days (actually 76) for marine ich.