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The temperature for Fish

Bradders

Bradders

Member
Joined
11 Dec 2023
Messages
808
Location
United Kingdom
Hello All,

When you scan the internet and read research, you find lots of different advice for species fish temperatures and the ranges that they can live in. I am talking more about adult fish, rather than breeding, which sometimes requires a more specific environment.

I just wondered whether people on UKAPS have performed any experiments, like reducing the temperature to 23 or raising it to 26, to see any noticeable difference in the fish behaviour or anything detrimental that has been observed - such as lethargy or aggression?

I have moved my temperature to just below 23C and up to 26C and could see nothing to indicate this bothered the fish. But then again, that is all within a tolerance (well, the wide tolerance range which exists on the internet!) of livebearers and tetra.

So, has anyone had any temperature experiences they can share? What have you observed, and why have you settled on one temperature over others?

Thanks,
Brad
 
I think 22-23 degrees is fine for most species. That also suits many aquascapers too. Open top tanks loose a lot of moisture to evaporation, even more to transpiration if plants are emergent, and this helps keep it to a minimum
 
Depends on fish; 25c is my standard temperature but I tend to do a lot of research on the fish I keep so that I set the heater to be that of the average water temperature for that fish at their known wild locations.

I mostly keep wild caught fish, however farmed fish tend to be in warm places that get cold over night - creating some adaptability 👍

Unless keeping temperate fish, I generally wouldn’t go below 22c
 
Tim Harrison said:
I think 22-23 degrees is fine for most species.
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castle said:
Unless keeping temperate fish, I generally wouldn’t go below 22c
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I also agree that down to 22/23 is going to work for most (non-breeding) freshwater fish. What I find strange is so much of the internet and LFS is 'pinned' on 25C. Maybe that is just a general and safe range that works for many.
 
I go with 25 C for my covered tank. I always unplug the heater when doing maintenance and of occasion forget to plug it back in. That sends the temperature down to 20C. At the lower temperature fish that would be reasonably active in the upper/middle part of the water column all go to the bottom of the tank and become much less active. It's a pretty obvious effect - the other day my wife gave the tank a casual glance and asked if I had forgotten to plug in the heater and sure enough that was the case. These are rummy-nosed tetras, 5 (probably 6 actually) banded barbs, and ember tetras.
 
Andy Pierce said:
I go with 25 C for my covered tank. I always unplug the heater when doing maintenance and of occasion forget to plug it back in. That sends the temperature down to 20C. At the lower temperature fish that would be reasonably active in the upper/middle part of the water column all go to the bottom of the tank and become much less active. It's a pretty obvious effect - the other day my wife gave the tank a casual glance and asked if I had forgotten to plug in the heater and sure enough that was the case. These are rummy-nosed tetras, 5 (probably 6 actually) banded barbs, and ember tetras.
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Interesting. So you do see a difference in the behaviour (i.e. increase lethargy) as you head down to 20. Is there a point (i.e. 22) where you see that start to occur?
 
I only got my tank a few months ago (it's set to 23⁰C) but I'm curious what happens to the water temperature in summer, especially when there's a heatwave and it can reach 30⁰C during the day in my flat? I quite like the idea of having some seasonal variation in temperatures, so long as it's not too much.
 
Katharine said:
I only got my tank a few months ago (it's set to 23⁰C) but I'm curious what happens to the water temperature in summer, especially when there's a heatwave and it can reach 30⁰C during the day in my flat? I quite like the idea of having some seasonal variation in temperatures, so long as it's not too much.
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Mass deaths in the marine world, and of course plenty of deaths in the tropicals too. 30c is very warm for any prolonged period for a lot of fish.
 
Katharine said:
I only got my tank a few months ago (it's set to 23⁰C) but I'm curious what happens to the water temperature in summer, especially when there's a heatwave and it can reach 30⁰C during the day in my flat? I quite like the idea of having some seasonal variation in temperatures, so long as it's not too much.
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castle said:
Mass deaths in the marine world, and of course plenty of deaths in the tropicals too. 30c is very warm for any prolonged period for a lot of fish.
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Well, this is one I can answer! (Well, at least from a freshwater perspective with livebearers and tetras).

My home gets very hot in the summer and the highest reading on my tank was 29C - and that persistent on and off for several weeks of last summer. At night, it would go back down to 24C ish.

This fish took the variation, and there were no casualties over the summer. I did not like that temperature in the aquarium of course, but the fish seemed quite resilient.
 
Bradders said:
Well, this is one I can answer! (Well, at least from a freshwater perspective with livebearers and tetras).

My home gets very hot in the summer and the highest reading on my tank was 29C - and that persistent on and off for several weeks of last summer. At night, it would go back down to 24C ish.

This fish took the variation, and there were no casualties over the summer. I did not like that temperature in the aquarium of course, but the fish seemed quite resilient.
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That's good to know, thank you! I assume with evaporative cooling it stayed cooler than ambient temperatures too?
 
I agree it's weird that the standard is so warm. I don't heat my tanks at all, but I keep my house on the warmer side (it doesn't get that cold here, so the extra heating cost isn't bad) and stay away from fish that really need the heat. My fish are lively and healthy and I feel good about it.

It is limiting though. I have a heater and an inkbird ready to go for my next tank because just a few degrees (fahrenheit) warmer in the winter would allow me to keep so many more species comfortably.
 
Katharine said:
That's good to know, thank you! I assume with evaporative cooling it stayed cooler than ambient temperatures too?
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Yes, the room was hotter than the aquarium was at its peak.
 
It is easy for those living up north to keep tanks in the temperatures mentioned in this topic, but in equatorial lands, tanks simply stay between 26~30ºC all the time, and during heat waves go above that. Around here, if someone says the temperature of the tank is 25ºC, inevitably someone else is going to say that this is going to kill their fish as it is basically freezing.

Fishes adapt to the environment and will be OK in a very wide temperature range. Temperature oscillation, on the other hand, I imagine that can stress the more sensible species.
 
22 degrees seems to work for my plants, fish and shrimp and keep evaporation to a minimum. I would like to go down to 20 degrees and keen to hear from others on this. I suspect warmer Summer temperatures prompts shrimp and fish breeding.
 
Malarky said:
22 degrees seems to work for my plants, fish and shrimp and keep evaporation to a minimum. I would like to go down to 20 degrees and keen to hear from others on this. I suspect warmer Summer temperatures prompts shrimp and fish breeding.
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My personal opinion is that 21 is on the low side. I have experimented with 22-23 for prolonged periods, and the fish have not batted an eyelid. There is conflicting reporting that fish can go down to 19-20, but I have chosen to stick to above 23. But that does not mean I am right, and it might work for some environments and fish!
LMuhlen said:
It is easy for those living up north to keep tanks in the temperatures mentioned in this topic, but in equatorial lands, tanks simply stay between 26~30ºC
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I have a 'bad' placement of my aquarium in a room that gets hot. All summer last year the tank hit 28 degrees + during the day. Have to say they survived just fine and were bombing around like they usually do.
 
I think at the lower end a degree can make huge difference. Personally wouldn’t go below 23 degrees. At the middle to upper acceptable end I think there’s perhaps a little more wriggle room. But obviously extremes at either end are not a good idea, especially for prolonged periods.
 
Heater failed two nights ago, and the tetras in that tank went down to 12c

They were lethargic, pale and not looking good. Pretty sure I’d have lost them if I did t catch it sooner (within 24 hours)
 
castle said:
Mass deaths in the marine world, and of course plenty of deaths in the tropicals too. 30c is very warm for any prolonged period for a lot of fish.
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Dissolved Oxygen levels for some fish can become an issue at 30 and above
 
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