Guppy Population Density

Michael Langerman
5 min readJun 24, 2020

Here is my oldest 1.6 liter aquarium on October 6th, 2018 after I added a young couple of dwarf guppies.

The first breeding couple had 13 drops with a total of 90 babies that were moved out of the tank for inline selective breeding of a dwarf guppy strain.

I need my adult dwarf guppies to be under 2 cm long for self-sustaining aquariums.
And they have to breed less.
Otherwise no aquarium of any size would be enough to support them all.

The new couple had their first baby on April 19th, 2019
This time I am going to keep all newborns with their parents in the aquarium.

Four months later on August 22nd.
There are total of 4 babies of different drops.

I allow plants to grow thicker to make more hiding spots for fry to rest and to enforce an advantage for smaller sized fish.
Once in a while I still have to remove some of the plants.

This is the aquarium on March 14th, 2020
It’s hard to count all the fish in this thicket of plants.

I count a total of a dozen fish, mature adults and fry.

May 18th, 2020
The largest, about 2 years old guppies are about 2,5 cm long.

I did not change the water in this aquarium for about 4 years now.
The accumulated residue is about 1,5 cm with gravel.

Amazingly, it did not change from the previous year!

I decide to disassemble this aquarium — let’s count the fish.

I use a pipette to move fry and young guppies.

And I use a net to move large adult fish.

One year of breeding and keeping all fish in the same aquarium yielded a total of 14 adults and fry guppies.
That is 6 times less compared to when I remove newborn fish.

Okay. Let’s move all the fish into a new 3 liter mason jar aquarium garden.

This aquarium is twice as spacious compared to the old aquarium.
That is where I am going to continue observations on the population density and to test new ideas with regards to self sustainable aquariums with fish.

A couple things became obvious already.
First of all, limited aquarium space reduces the breeding rate of guppies greatly.
And secondly, adult fish seem to grow smaller — without me making such selections.
That is exactly what I need for my self sustainable aquariums ;)

Now, let’s get to the old aquarium for the final look.

I have already removed all plants and drained the water.
All you can see is the gravel with dirt accumulated over a 4 year period of time.

And here you can see adult scuds — gammarus hiding in the gravel and feeding on the waste.

More about scuds and other aspects of self sustainable aquariums in my previous and future videos.

Have fun and happy aquarium gardens :)