Many beginning aquarists take the “kid in a candy store” approach to populating their tanks. This is a serious mistake for many reasons.

You will likely buy too many fish and not pay proper attention to population management in terms of compatibility.

Rather than simply going to an aquarium store and “window shopping,” it’s best to plan your tank population in advance. Err on the side of less is more, and make sure the mix of fish you’re considering can cohabitate peacefully.

Things to Consider Before You Buy

There are many theories about minimizing aggression and territoriality in a tank. Of these, maintaining a good mix of fish from different families can go a long way toward keeping the peace. Aggression in fish is typically directed toward their own kind.

This response may be purely instinct on the part of the fish. They know what they like to eat, so by attacking their relatives who want to eat the same things, the fish is simply protecting what he sees as a limited food supply. This holds true even in an environment where ample food is provided.

It’s also important to consider the vertical and horizontal spaces in the tank and to select species that occupy different niches and zones.

Obviously if you overstock a particular region of this enclosed environment, you’re setting the stage for an underwater turf war.

It’s always a mistake to just go for the “pretty” fish, or the ones you find attractive for other reasons. Population management has to be based on a complete understanding of how any one fish will live and behave in the tank.

For beginners, stick to the one inch (2.54 cm) of fish per 5 gallons (18.9 liters) of water rule.