Aquarium: which volume to choose?

What fish population for an aquarium of what size?

 

This is a recurring question, to which there is no simple answer.

And, as always with complicated questions, there are simple dogmas, perfectly wrong, but which allow one to pretend to have an answer!

 

As a young fishkeeper (so a long time ago!), I learned, like everyone else, THE rule: "one centimetre of fish per litre".

It has some variations, such as subtracting from the water volume the substrate and a margin for the fill level, but overall, it is the only clear rule given to beginners who ask the question.

 

Yet, it makes absolutely no sense.

Because it is based on a criterion that has no relevance: the length of the fish.

 

 

Indeed, the length of the fish does not determine its metabolism at all: neither its oxygen needs, nor its food needs, nor filtration, nor water purification, nor the volume of its waste (excrement, CO2...).

What best determines an animal's metabolism is its live weight.

 

 

A friendly danio (the famous "zebra fish") measures 4 cm and weighs 0.5 grams.

While an average goldfish measures 10 to 15 cm for... 100 grams (the goldfish scandal)!

The goldfish is 3 times longer, but 200 times heavier.

And when it reaches 45 cm, once adult, it weighs 2.5 kg, which is only 11 times the length of a danio, but 5,000 times its weight!

Would we put a 45 cm goldfish in a 45 litre aquarium?

 

 

In fish farms, a powerful filtration and strong oxygenation allow staggering fish concentrations. With a probably disastrous level of well-being (fish happiness and animal well-being).

 

The most widespread dogma in fishkeeping is therefore false.
It does not even allow approaching any reality. It corresponds to nothing, except the idea of the one who spread it at the start.

 

On the contrary, if we take the problem differently, we can try to rely on the natural conditions of the species.
For a territorial fish, bottom dweller or very active swimmer, the surface area makes more sense than the volume.
But above all, a free fish has several cubic metres of water all to itself. The natural population density is very low, with thousands of litres per fish.

And that is not feasible in your living room!

 

So a compromise will have to be made.

Between the ideal of 10,000 litres per guppy and the obvious constraint of the square metres of our apartments.

My dream, never realised, was an infinitely long aquarium, not necessarily deep, which would house fish like a riverbed, whose sections are alternately planted, free, sandy or deep, dark then bright. Populated, above all, by very small species (platy variatus: hardy fish in aquarium).

In short, an aquarium so long to travel for the fish, compared to its size, that it almost forgets captivity.

 

Some have solved this with the keeping of shrimps, which swim little and spend their life in a small space. It is a solution.

 

 

 

Others (and you are increasingly many here) have created fishless aquariums, housing all kinds of critters, from fascinating micro-fauna to snails, including Blackworms and water lice! (the fishless aquarium phenomenon)

Aquatic gardens providing the living room with soft light, where something is always happening, and where size matters little, since its inhabitants are tiny!

For your fish to reproduce under these conditions, you need to understand the key to their reproduction (the key to fish reproduction) and ensure the water temperature is suitable (what temperature for an aquarium?).

Finally, to ensure they stay in good shape, it is useful to know their natural rhythm and sleep (fish sleep: do they sleep?), and to know that fish can safely eat certain foods (can fish safely eat tubifex?).

And if, for some species, you want to avoid problems related to goldfish, it is better to know the precautions to take (putting an end to goldfish indoors).