What temperature for an aquarium?

The ideal temperature for an aquarium is often debated.

Generally, there is agreement on 24°C. This is for tropical species, of course.

For Amazonian “biotopes” (Discus, cardinalis, etc.), it often goes even higher (what temperature for an aquarium?).

 

 

Aquarium-keeping manuals mention quite precise temperatures for each species, and sometimes there is a dilemma when one wants to keep several together.

 

An unsuitable temperature is obviously a source of stress for the organism (fish happiness and animal well-being).

For a fish, it is quite different from what we might imagine. In our case, cold makes us shiver and heat makes us sweat. But this is because our body struggles to stay around 37°C, whether it is 0°C or 35°C outside.

For fish, it is different. Their body temperature varies with that of the water. They are therefore much more subject and sensitive to it, since their metabolism must function at this temperature, without them being able to change it. Some enzymes made to work optimally at 20°C work less well below or above that.

 

 

Unlike ours, the metabolism of fish does not require 37°C to function (far from it!). It is adapted to temperature variations, since it is subject to them. Each species has its optimum. But it is only an optimum, not a strict requirement (unlike our 37°C).

A goldfish outdoors (where it feels best) goes from 5°C in winter (or even less, slowed down at the bottom of a pond) up to 25°C in summer (the scandal of goldfish).

 

But a trout will die if the water is warm, less because of the heat than because warm water is too poorly oxygenated.

Conversely, a Discus will not tolerate cool water and will fall ill, then die, its metabolism faltering at low temperatures.

 

Should we conclude that, apart from goldfish, all fish live with their nose on the thermometer?

 

No, because experiments carried out in trash tanks have shown that, within certain limits, temperature can appear as a relatively secondary factor (the phenomenon of aquariums without fish).

Important, but secondary.

For example, a tropical fish placed outdoors in summer will choose its temperature by rising to the surface or descending to the depths. Indeed, there can be a 6°C difference between the surface and the bottom of a trash tank in summer. Yet it will not hesitate, to avoid your gaze or chase a daphnia , to dive in a few seconds, thus enduring without problem a significant difference.

 

Finally, I personally collected guppies, platys, and swordtails at the end of October in water at 11°C. They were in full health, with incomparable colors and an astonishing vitality in the net (platy variatus: hardy fish in aquarium) ! They would never have tolerated that in an aquarium.

 

 

It therefore seems that the theory of cumulative stresses applies to fish as to other animals: a stress (within reason) is a stimulus that brings well-being or excitement, but the same stress, if combined with others in excess, becomes harmful, even deadly. Beyond a certain threshold very difficult to assess, and probably, as for us, different depending on the individual.

The pleasure of a varied life in a trash tank (natural food, rain and wind, green water, calm, etc.) largely compensates for the micro-aggression of temperature. But in an aquarium, it adds to noises (filter, bubbler, pumps), captivity (transparent walls, view of humans…), industrial food, overcrowding, etc. And there, the fish’s tolerance (or even its pleasure) regarding temperature variations becomes low, even nil. Temperature then becomes "the stress too many" (putting an end to the goldfish indoors).

 

 

Once again, we face the issue of the fish’s pleasure.
A new field of research, long ignored, but clearly fascinating! (fish sleep: do they sleep?)

Aquarium-keeping is finally evolving, and that is all to the good.

To feed your fish properly and avoid any stress, you must understand their feeding and breeding (the key to fish breeding) and adapt the size of your aquarium (aquarium: which size to choose?). Finally, some foods can be given without risk (can fish safely eat tubifex?).