plebian
Fish Fanatic
I don’t think most people give it a thought, but an aquarium is at best a form of gilded cage. Some poorly kept aquariums are more like a Turkish prison, overcrowded and polluted. Overcrowding is the rule, even among better kept aquariums.
The old “one gallon per inch of fish” rule is wholly inadequate for all but the smallest fish. As far as maintaining water quality, the mass of a fish is more important than its length. Assuming adequate water quality, the length of the aquarium, not the fish, should then take precedence.
There are very few species that don’t spend most of their time swimming, and even the smallest species benefit from longer aquariums. Water depth is simply not very important except perhaps for some of the larger species, which probably shouldn’t be kept in any hobbyist aquarium to begin with.
It is my personal opinion that nobody should be keeping any fish, no matter how small, in an aquarium less than 36 inches long. There are exceptions, like Betta splendens, but they are few. Even smaller tetras, like neons, appreciate swimming space. Smaller fish are typically found in schools, or shoals, as a means of avoiding predation. They are always more comfortable in groups, the smaller the fish the larger the group. The larger the group, the longer the aquarium.
For example, I currently have 9 cardinal tetras in my 180 gallon aquarium. Except when actively feeding, their group typically occupies a volume of water roughly measuring 12”H x 18”W by 24”L in the middle of the water column. That’s equivalent to 22 gallons of water.
Since you cannot fill a tank to the top with water, and since you would need some substrate and some plants and/or driftwood for shelter, you would need a 29 gallon tank to provide an minimum optimal volume of water. But a 29 gallon tank would not meet the horizontal space requirements of a group of 9 tetras, since it’s only 12” wide. The smallest standard size tank that would accommodate an optimal swimming space for a group of 9 cardinal tetras is a 40 gallon breeder.
Most hobbyist resources recommend minimum acceptable aquarium sizes for any given species. While it is possible to maintain healthy fish according to these recommendations, it seems the word “minimum” is frequently overlooked. Minimum conditions should not be interpreted as optimal.
Aside from requiring increased maintenance, smaller aquariums frequently have a negative effect on species behavior. This is especially true of community aquariums. Most species do not naturally mingle with other species. Each needs their own space to be comfortable. In fact, even members of a single species require what might be called their personal space. This is obvious among territorial species, but even shoaling species require personal space.
In the example I gave above for a small group of 9 cardinal tetras, each fish typically maintains a distance from its nearest neighbor of from 4” to 6”. That distance shrinks when other, larger species are nearby. This is what is referred to as schooling behavior. It is a defense mechanism used to avoid predation.
Very few species form schools unless threatened. Instead, they spend most of their time congregating in loose groups referred to as shoals. While schooling behavior is highly valued by most hobbyists, in most cases schooling behavior is an indicator of stress. Brief episodes of schooling are perfectly normal and healthy among shoaling species. But frequent occurrences are an indicator of unusual levels of stress and something to be avoided.
Like many, when I was young my parents purchased a small (10 gallon) aquarium and overstocked it with swordtails, mollies and guppies as a form of entertainment. The aquarium had no filtration, only an airstone and the substrate consisted of colored marbles. Needless to say, the fish did not survive long.
The first aquarium I purchased as an adult was a 30 gallon equipped with an undergravel filter. Initially, I kept a few goldfish. That was before I learned how large goldfish could become. I replaced my 30 gallon with a 55 gallon which I later populated with 4 adult discus. At the time, and even to this day, most discus keepers will tell you that’s perfectly acceptable.
Even though I had relatively little knowledge at the time, as I observed the behavior of my fish I realized that a larger aquarium was necessary. I told myself then that if I ever owned another aquarium it would be at least 125 gallons.
Now, many years later, I have a 180 gallon aquarium. I designed and built it myself with the goal of maximizing swimming space. Unlike a traditional 180 gallon aquarium which provides 6 linear feet of swimming space, my custom built aquarium provides 9 linear feet of swimming space.
My aquarium currently houses 5 discus, 9 cardinal tetras, 4 emerald Corydoras, one dwarf spotted catfish, one bristlenose catfish, and one red lizard catfish. I consider this very close to a maximum optimal stocking level.
The old “one gallon per inch of fish” rule is wholly inadequate for all but the smallest fish. As far as maintaining water quality, the mass of a fish is more important than its length. Assuming adequate water quality, the length of the aquarium, not the fish, should then take precedence.
There are very few species that don’t spend most of their time swimming, and even the smallest species benefit from longer aquariums. Water depth is simply not very important except perhaps for some of the larger species, which probably shouldn’t be kept in any hobbyist aquarium to begin with.
It is my personal opinion that nobody should be keeping any fish, no matter how small, in an aquarium less than 36 inches long. There are exceptions, like Betta splendens, but they are few. Even smaller tetras, like neons, appreciate swimming space. Smaller fish are typically found in schools, or shoals, as a means of avoiding predation. They are always more comfortable in groups, the smaller the fish the larger the group. The larger the group, the longer the aquarium.
For example, I currently have 9 cardinal tetras in my 180 gallon aquarium. Except when actively feeding, their group typically occupies a volume of water roughly measuring 12”H x 18”W by 24”L in the middle of the water column. That’s equivalent to 22 gallons of water.
Since you cannot fill a tank to the top with water, and since you would need some substrate and some plants and/or driftwood for shelter, you would need a 29 gallon tank to provide an minimum optimal volume of water. But a 29 gallon tank would not meet the horizontal space requirements of a group of 9 tetras, since it’s only 12” wide. The smallest standard size tank that would accommodate an optimal swimming space for a group of 9 cardinal tetras is a 40 gallon breeder.
Most hobbyist resources recommend minimum acceptable aquarium sizes for any given species. While it is possible to maintain healthy fish according to these recommendations, it seems the word “minimum” is frequently overlooked. Minimum conditions should not be interpreted as optimal.
Aside from requiring increased maintenance, smaller aquariums frequently have a negative effect on species behavior. This is especially true of community aquariums. Most species do not naturally mingle with other species. Each needs their own space to be comfortable. In fact, even members of a single species require what might be called their personal space. This is obvious among territorial species, but even shoaling species require personal space.
In the example I gave above for a small group of 9 cardinal tetras, each fish typically maintains a distance from its nearest neighbor of from 4” to 6”. That distance shrinks when other, larger species are nearby. This is what is referred to as schooling behavior. It is a defense mechanism used to avoid predation.
Very few species form schools unless threatened. Instead, they spend most of their time congregating in loose groups referred to as shoals. While schooling behavior is highly valued by most hobbyists, in most cases schooling behavior is an indicator of stress. Brief episodes of schooling are perfectly normal and healthy among shoaling species. But frequent occurrences are an indicator of unusual levels of stress and something to be avoided.
Like many, when I was young my parents purchased a small (10 gallon) aquarium and overstocked it with swordtails, mollies and guppies as a form of entertainment. The aquarium had no filtration, only an airstone and the substrate consisted of colored marbles. Needless to say, the fish did not survive long.
The first aquarium I purchased as an adult was a 30 gallon equipped with an undergravel filter. Initially, I kept a few goldfish. That was before I learned how large goldfish could become. I replaced my 30 gallon with a 55 gallon which I later populated with 4 adult discus. At the time, and even to this day, most discus keepers will tell you that’s perfectly acceptable.
Even though I had relatively little knowledge at the time, as I observed the behavior of my fish I realized that a larger aquarium was necessary. I told myself then that if I ever owned another aquarium it would be at least 125 gallons.
Now, many years later, I have a 180 gallon aquarium. I designed and built it myself with the goal of maximizing swimming space. Unlike a traditional 180 gallon aquarium which provides 6 linear feet of swimming space, my custom built aquarium provides 9 linear feet of swimming space.
My aquarium currently houses 5 discus, 9 cardinal tetras, 4 emerald Corydoras, one dwarf spotted catfish, one bristlenose catfish, and one red lizard catfish. I consider this very close to a maximum optimal stocking level.
