Come across this interesting read when searching about temperature stability . Worth a look

[Richee]

https://aquariumscience.org/index.php/4-2-aquarium-temperatures/

 

[Ichthys]

Another aquariumscience article that gives zero consideration to stress. “It’s ok because not many died”. I take that whole site with a pinch of salt. Many bad articles based on bad practices that “seem to work…ish”, and not many based on actual knowledge.

 

[GaryE]

That is a hackwork article by a lazy writer, whoever that is.

There is a body of research that shows a few things Cory in the co-op has never worried his head about. Things like temperature dependent digestive enzymes, for example.

Ten minutes of research into one group (let's take Corys for the poetry of it) would have shown his blackwater ideal to be idiotic. 30 minutes looking at scientific sites would have shown that writer they weren't ready to post. But a no checks and balances internet probably means that'll be taken as gospel by its readers.

 

[Byron]

I am with others here. There is abundant evidence (have a look at the Manual of Fish Heath written by four leading UK scientists) discrediting much of this. Temperature is a prime issue for tropical fish. It drives the fish's metabolism, and this when sped up (as in higher temperatures) wears the fish out quickly. Others above have mentioned lower temperatures. The other thing is that no credence is given to actual habitat conditions, and these are no where near as flexible as this site suggests. The diurnal temperature is only a couple of degrees if that, and seasonally most of the rainforest is basically steady.

 

[TwoTankAmin]

I have actually read a number of research papers on temperature and fish. Most of them deal with a specific species and then what are the limits of temperatures that can survive and what temp will kill half. This is typically how anyfatal limits for fish are tested. What is the point which kills half. Oddly, most of these papers do not deal with how the save fish when they are going to be dying at extremes of hot or cold. The papers look at how the fish behave as they near the fatal temperatures.

Howeverm I did come across a paper which alaso asked, when the fish exhibit the behavior at either a very high or low temp. which indicates that hey will soon be dying, what is the best way to save them. The answer was pretty simple. As quickly as possibly return them to water withing their normal temperature range.

I have personally on several occassions seen this work to save fish and then failure to do this has resulted in many dead discus.

But what made me conclude that the paper that the OP's link leads to made a statement that show this paper is not worth reading. Look at the last two boxes iin the colored chart. They say two things that are absolutely false.
TDS must be over 60. But they neglect to say 60 what scale of measurement. If we assume it is PPM and I can te;l you I brought inported Altums intp a tank with TDS of 30ppm. TDS or conductivity matter.
KH and GH ro not matter. And I can agree with the KH part, fish have no KH requirements, But that doesn't mean that KH is not relavant because it does contribute to TDS.

Next, research papers are not all equal. There is a process called Peer Review which is utilized by most puiblishers. Before they will publish a paper they use a groups or scientist who are know experts in the relevant filed to review it. These folks are there to insure to the greatest extent possible, that the research was doen in a proper manner and that it support the conculsions.

So, the first thing i did when I saw the study the [a[er mention about discus and cold temps was to head over the Google Scholar so I could read the paper for myelf. Across the top of the PDF I linked to, it said the following (red added by me):

bioRxiv preprint doi: https://doi.org/10.1101/749705; this version posted August 29, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under
aCC-BY-NC-ND 4.0 International license.

When the paper was published it did say it had been peer reviewed. So I also checked that process for the paticular publication. I was not impressed. How peer reviewers are selected and how many are used fo a given paper matters. I think these folks are a little lax in the peer review process. But that is my opinion only.

So, as far as I am concerned the paper may or may not be accurate in its conclusions. For one, they did not deal with fatal temps and then at the coldest temps they only left the fish at them for 12 hours. What would have happened to the fish if they had stayed in those temps for a day or more? Usually, the general water temperatures at any given location (think depth especially) do not change on a 12 hour schedule.

The authors did get one thing right, different species have different thermal tolerances. Moreover, individual of a given species do not all have the exact same thermal tolerances. one fish may be fine at 14C for 12 hours while another fish may suffer a worse result. One way to see this is the next time you and a bunch of friend are out in cold weather, some of you will find it more objectionable than others as to how cold they feel and how badly then want to warm up.

I did find another paper where they fish were left for 24 hours but there the coldest temps was 20C not 14C.

Physiological responses to cold stress in the gills of discus fish (Symphysodon aequifasciatus) revealed by conventional biochemical assays and GC-TOF-MS metabolomics​

https://www.sciencedirect.com/science/article/abs/pii/S0048969718320588

However, I also came across the following information re discus in the wild and their waters temps. The information was collected by Heiko Bleher and sumarised in Practical Fishkeeping.

What temperature is the water where Discus live?​

Heiko Bleher has collected data on Discus habitats for the past 40-50 years, so he knows the answer to this one...

Each species is found in waters of a specific temperature and chemistry and they have evolved to live in these conditions over millenia. This is also why they are isolated from each other, except during extreme floods.

I have collected data on the water they are found in over the past 40-50 years and used scientific equipment and taken measurements at depths of 1.5-2.5m/5-8.2’ where the Discus live.

Symphysodon discus, the Heckel Discus, lives in water with an average temperature of 28.6°C/83.5°F. The highest I measured was 31.7°C/89°F in one biotope and the lowest was 25°C/77°F. S. discus is a blackwater species.

Symphysodon aequifasciatus, the Green Discus, lived in waters with an average temperature of 28.2°C/82.7°F through 1997. Prior to 1996 the average was 27.4°C/81.3°F. The highest I measured was 31°C/87.8°F and the lowest in its biotope was 24.6°C/76.3°F. It also lives in blackwater.

Symphysodon haraldi, the Blue or Brown Discus, lives in a water average at 28.8°C/83.8°F The highest temperature I ever recorded was 32.4°C/90.3°F and the lowest was 23.5°C/74.3°F.

It is the most tolerant, as regards water parameters and temperatures, of all three species.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine.

from https://www.practicalfishkeeping.co.uk/features/what-temperature-is-the-water-where-discus-live/

But here is an interesting challenge. Can anybody find reliable information on people who who report having kept their discus for fun, for breeding or for selling at 20C let alone 14C? I would love to see this info.

 

[Back in the fold]

Very interesting . The comments , not the article .

 

[Richee]

Very interesting . The comments , not the article .

There’s some good points given , it’s a whole book not just one article and there cited scientific research listed for every topic

 

[Richee]

But he is right about tropical fish and their water habitat going through rapid temperature changes in the different water layers and they swim through all of them with no harm done to them . How are they about to do it in the wild and not in our tanks ?

 

[gwand]

If you think the author’s comments merit attention then set your tank at 85F or 55F and see what happens. That’s not an experiment worth trying.

 

[Richee]

If you think the author’s comments merit attention then set your tank at 85F or 55F and see what happens. That’s not an experiment worth trying.

He didn’t say that they would be fine at a constant temp of 85 or 55

 

[Byron]

But he is right about tropical fish and their water habitat going through rapid temperature changes in the different water layers and they swim through all of them with no harm done to them . How are they about to do it in the wild and not in our tanks ?

This is not the same thing, far from it. It is certainly true that fish live at different water levels, as the text from Heiko Bleher explained. And I noted in my larger tanks that there was a difference between water near the substrate and closer to the surface. But this is not the same as what is being proclaimed in the article. Far from it.

 

[Richee]

This is not the same thing, far from it. It is certainly true that fish live at different water levels, as the text from Heiko Bleher explained. And I noted in my larger tanks that there was a difference between water near the substrate and closer to the surface. But this is not the same as what is being proclaimed in the article. Far from it.

I think he is trying to say that a temperature change a couple degrees , rapid or not , isn’t going to harm them . Should you keep your fish at 85 or 65 no but I’ve seen a lot of people saying that even a 2 degree drop at night will kill the fish eventually and I just don’t agree with that from all the research I’ve done . My tank would drop 3 degrees maybe at night some nights and I went and got a huge heater but a few degree drop in the range over night and a few degree increase as the day goes on isn’t going to hurt them

 

[Richee]

This is not the same thing, far from it. It is certainly true that fish live at different water levels, as the text from Heiko Bleher explained. And I noted in my larger tanks that there was a difference between water near the substrate and closer to the surface. But this is not the same as what is being proclaimed in the article. Far from it.

I’m wanting to see research on WHY it temperature changes are detrimental to the fish, by a couple degrees in their range. Not to prove anybody wrong I am always down to learn something new if I’m misinformed

 

[GaryE]

All of the fish we caught this summer, along the equator in Central Africa, had their water tested. The standard temp was around 23-24. None were higher than that, even though the air was pretty well always 26.

The article is unimpressive because it overgeneralizes. I worked with tropical fish in a cold climate for years, and I've seen ice in fish bags from South America and Africa - airlines do what airlines do, and not just to your baggage. No fish survived the ice, but in the next layer of boxes back, they could be saved in most cases by sudden immersion in warm water. That would be worthless data, because it reflects nothing but a hobby situation.

When my fishroom water fell to 1 degree C in a 1998 icestorm, all fish were dead by 10 degrees. It proves only that they are not adapted to ice storms.

I detect some cherry picking in that article, though I see that for the majority of tropical species in our tanks, 23 is a good temperature. For Discus, cardinals and other warm water fish, it isn't. I heat those tanks.

For breeding fish, each species has a range you adapt to.

Somewhere I read a serious paper suggesting a 3 degree celsius drop entered the danger zone for most fish. It's a rule I've followed with zero issues. The thermocline issue is fun, as a number of species are differentiated by their depth in lakes. They sense temperatures and stay in their zone so rigidly it's a barrier to interbreeding and a motor in species formation. I believe the relatively recent discovery of a Pseudocrenilabrus species flock in Lake Mweru, DRC, bears that one out. Who assumes tiny fish live at all levels of a lake? Larger fish can, but.

Out there somewhere is a paper trying to explain why different Aphyosemion killie species in an African river stay in their own stretches and don't mix, or even seem to compete. Outwardly @Richee , they are similar enough, but one species starts appearing where sun warms the water 2 or 3 degrees, and the other stays in shaded water a couple of degrees cooler. The discovery was they had temperature dependent digestive enzymes, and those enzymes could not adapt. The cool fish in the warm water grew more slowly, were sluggish and easily predated, and were completely outcompeted (especially young fish) by their warmer water cousins. It went the other way too. The conclusion was climate change could decimate species in the region.

But no studies have appeared to follow up - no one wants to pay people to study that. I can say that all the fish studied as needing the cooler (20-22 range) are ones considered hard to breed in aquaria, and the warmer ones are generally seen as easy.

I do all water changes a degree or two above tank temperature, especially in quarantine, as I have observed that fish facing sudden temperature drops are more prone to Ich, if it's present. I'm not sure about velvet, although I've wondered. But that's for short term drops of a few hours. Certainly fry growth at either species extreme is slowed. If you crank the heater thinking you can speed the growth of a fish from 22 degree water, you get weak fry, as bad as if you raise them at 17.

We also have that curious question of bacteria in our tanks, and fish, and not just parasites like Ich. Different bacterial diseases have their own temperature needs. That is a factor - nothing exists in isolation.

 

[Byron]

I’m wanting to see research on WHY it temperature changes are detrimental to the fish, by a couple degrees in their range. Not to prove anybody wrong I am always down to learn something new if I’m misinformed

Temperature governs the fishes metabolism, how their internal processes function. Mammals like us have a set temperature. When it goes high we suffer, from fever or just exhaustion, and the opposite way from hypothermia. Fish are ectotherms, and there is plenty of evidence how just a few degrees can affect this. The temperature in the habitats does not fluctuate more than a very few degrees. If I read the initial post correctly, there was more than this involved (it has since been removed).