Dipping a toe in colder waters

[JMorgan]

Recently I've been intrigued by some snippets of info I picked up watching videos made by a young Aussie fishkeeper based in Brisbane. Go north up the coast from Brisbane along the Sunshine Coast and you get to the Great Sandy National Park where he's made a few videos of him and friends observing and collecting various species of Rainbow fish. Anyone who's enjoyed the Ivan Mikolji underwater videos of Venezualan freshwater biotopes will probably enjoy these. The channel is called KeepingFishSimple.

However the point is that on many occasions they're remarking on how "f'ing freezing' the water is they're snorkling in. On one occasion they state the water temperature to be around 16˚C. Bear in mind that typical swimming pool temperature in the UK is 26 to 28˚C , with pools for kids being around 30 ˚C, or quite a bit hotter than the 24 to 25˚C I've been keeping my fish at for years!

In other videos, where he's doing fish room tours with local (to Brisbane) fishkeepers, it turns out these guys are routinely extending their mostly indoor hobby with numerous outdoor tubs and ponds. While these get a lot more use in summer time (as is the case in the hobby the world over), it would seem it's not unusual for a great many tropical fish species (typical of UK community tanks) to over-winter outdoors in these tubs.

Now initially I shrugged this off, mostly because I've been to Brisbane and it was bloody hot, to put it mildly. But again, some off-the-cuff comments are made on the videos: one of which reported winter temperatures getting down to around 0 ˚C (which amazed me) - with the fish in these outdoor tubs being perfectly OK, not merely surviving, but going on to thrive and breed the following summer. Anecdotal for sure, but intriguing even so . . .

So I did a bit of research online and it turns out that, while such exceptionally low temperatures aren't typical, nor is it all that unusual for night-time winter temperatures to drop below 5 ˚C, with the mean temperature during the winter months being around 15˚C . I assume that this mean ambient temperature would approximate the water temperature in the outdoor tubs, especially the larger ones. i.e. around 14 to 16˚C.

My guess is that the semi tropical climate in Brisbane has created a different mindset to the hobby in general: Where those of us in the UK tend to assume, with good reason, that (except for the brief summer months) our climate will kill tropical fish, while those actually living in areas of the world some of our fish come from, have a more pragmatic perspective.

Chief of which includes the understanding that, especially semi-tropical fish (versus equatorial tropical where temperatures fluctuate much less), are evolved to cope with quite considerable seasonal fluctuations in temperature. Spending months on end in temperatures we humans would experience as intolerably cold.

Anyone who's swum in tropical waters will also appreciate that temperatures plummet the deeper you dive - that whizz to the surface and back so typical of corydoras could easily see them swimming through several degrees of temperature differential within a few seconds - so it's not just a gradual seasonal change we're talking about. Then, of course, there's the lowering of temperature through rainfall / Andean melt water, flooding etc. which is more gradual, but still pretty abrupt and which plays a huge part in triggering breeding cycles.

Apart from giving me pause with regard to questioning whether I really need to be heating tanks in a house that never drops below 21˚C, (especially if I pay more attention to species selection), I'm also wondering about the consequences of effectively depriving our fish of the seasonal fluctuation in temperature with thermostatically controlled heaters? What about the depth differential that's non existant in a heated tank with good circulation? Might they be healthier and more fecund if allowed a period of semi-dormancy during the winter? Might they be healthier if given an environment with clearer temperature gradations allowing them to seek out cooler or warmer areas as needed?

No idea how you'd recreate a lower temperature with depth indoors, but I suspect that might be part of why fish tend to thrive in summer tubs.

I need to do a lot more research, especially regarding species distribution ranges, as I realise I've previously (and I'm ashamed to say that 'previously' is now quite a few decades!) been far too vague and generalised in how I thought about such a critical factor as temperature, with far too great a tendency to just lump all fish living between the tropics into one conveniently broad category - that's gone hand in glove with a set and forget attitude to my heaters' thermostats.

Your thoughts and experiences?

 

[Heelllooo]

From my meager experience what I think :

Those question are really species dependant.

For exemple, I would take a lot of precaution with fish that lives in equatorial climate rivers or big water volume that don't tend to fluctuate a lot.

But sp. that lives farther from the equator and also fish that tend to lives in small water volume ( small rivers, small pools of water in the wild ) can handle pretty big and fast changes. I've been doing nearly 50% WC with water 5 degree celsius or more less than my tank water stock with apisto Borelli ( which is subtropical and can be found in really small rivers ) and Amano. No issue.

I've read a lot about people doing big and cold WC before doing so and it's really hard to find report of people having issue

I agree that in general in the hobby we tend to clump all tropical and subtropical fish together and underestimate how much a healthy fish can handle temperature variation and temperature outside its optimal range.

However I would advise to always do things with cautions and research the real natural condition of the fish habitat before trying anything.

 

[Myrtle]

As above, it's def species specific. As you say though, it's worth researching the origins of the species even if they have been tank bred for generations. How many generations would it take to revert to being adaptable to temp fluctuations again? I doubt the domestic strains would manage well, but some of the species that haven't been messed about with too much may do better.

 

[Oldguy]

No idea how you'd recreate a lower temperature with depth indoors, but I suspect that might be part of why fish tend to thrive in summer tubs.

Interesting post.
Try a large tank with no water movement. As a kid I found temperature gradients in my tanks, a heater in one corner and no pump or air stone. Fish were not that happy. Houses back then were just cold.
On a planned project a deep tank with a heater halfway up and little or no turn over of water should give a temperature gradient with depth but even the deepest 'home' tank would be shallow compared with a natural pond or lake.

 

[jaisol]

I agree with the above.
Rivers / lakes, can have 10- 18F variations from shallows banks to depth, I think problems arise when fish are at either their upper or lower extremes and then there is a further sudden change.
My neo-caradina shrimp happily survive and are active down to about 52F (not gone below that yet), However bristle nose plecs have problems with water changes if cooler water around 52F is added to tank water around 55F, warmer WC water and no problems. For other tropicals I have left the heater off once or twice after maintenance and had drops down to the low 60s without incident.
Plants, dropping the temp slows growth with some appearing to be dormant over winter, one or two have died (java fern does not like low temps).