A myth that I am sure everyone has heard, is that a fish will only
grow to the size of its container. This is something I believe---If
you disagree with me just stop and think about it for a minute. A fish
obviously does not grow larger than the container it lives in...right?
The ugly fact is that it generally dies when it reaches the maximum
size that the container can handle, thus no longer growing
and
making this a catchy yet convenient myth, more conducive to buying
fish indiscriminately.
There is also the one inch per gallon
rule, a grossly
inadequate system for estimating the amount of fish an aquarium can
handle, but it persists. Why?
Well, for one thing it is generally true. It gives a rough biomass
to aquarium size proportion that is pretty accurate for the type of
fish a novice usually thinks of (guppies, tetras and other
community fish
). To get more specific than this gross
generalization, we have books and magazine articles in which the
authors give us minimums which are required for keeping
certain species of fish. Granted, many authors and experts will give
the more fuzzy recommended for things such as tank size
(gallons, liters or tank length), but I always wonder what it is that
these seemingly reasonable numbers are based on. Is it experience? Is
there some sort of calculation you can use? What?
If I were to make up rules about tank sizes required for certain fish or the number of fish which can be supported in certain sized tanks, I would start with the actual physical size of the fish. In general I believe it is a bad idea to have a tank that is smaller in length, width or depth, than the length (or height) of the fish kept in it.
This is a nice rule (lets call it rule #1) that I would like to see followed when it comes to fish such as cichlids or characins, but I would say this rule can be affected by the flexibility or lifestyle of the fish in question. A 3 foot fire eel can be well maintained in a fairly narrow tank, and exceptions are easily made for fish with these sorts of unique characteristics.
Following the physical size of the fish, rule #2 would focus on the means of locomotion... or the way the fish swims. I like to see a fish wag his tail a few times while swimming the length of his tank, so I think a five-fish-length rule is good for fish who like to swim freely---of course not all fish swim in the same manner and that is where more exceptions can be made.
Predatory fish that prefer to lurk, like some of the large South
American catfish, seldom swim any length greater than the distance to
their next meal. Other fish I would make exceptions for are those like
the knife fish --which swim forward or backwards equally wellor
plecos whose flat bodies tend to scoot
along either horizontal or
vertical surfaces.
The final Rule (#3) I would consider for tank size, would have to be the most import and variable one. What amount of work we as fishkeepers are willing to do to keep the water healthy. Excellent filtration and massive daily water changes would keep a very small environment healthy almost regardless of the fish load living in it---but daily water changes are absurd (well, unless raising very delicate fry but even that would have to end after a while).
I generally target a 1/4 water change weekly, keeping nitrates in the 20-40ppm range. If I cannot do this I either reduce fish load or add plants. Currently, all my home tanks have nitrates in this acceptable range even though my water change schedule is sometimes not the 1/4 tank weekly I like to tout.
Now that I’ve laid the foundation for the way I do tank size estimations in 3 simple rules, I’d like to share some small-tank set-ups I have done successfully.
I’ve kept a fancy goldfish alive, healthy and growing in a two gallon bowl, even though some experts believe that you should have at least 20 gallons for each fancy goldfish. I was very uptight about water changes and feeding and in the course of his first year he grew from 1.5 inches (2 counting his tail) to a healthy 3.5 inches (5 with tail). By the end of his second year he was upgraded to a 15 gallon tank and eventually ended his days in a 100 gallon tank with many friends and relatives present. Some of you may remember his bowl show appearance in 1996 as the $1.98 goldfish.
Currently, I have 2 small tanks (2.5 gallons) set up and running, one is a small family community of the midget livebearer Heterandria formosa [see article by Dave Sanford in January’s NW Aquaria], and the other is an experiment started on May 1st, 1997.
The Heterandria tank (using undergravel filtration and no heater) currently has mom, 14 offspring, an otocinclus and a few snails. There is a small piece of bogwood, some Java fern and Java moss, and lapis luster natural gravel that keeps the Ph buffered up a bit between water changes which only happen about once a month.
My experiment which I started in May, is a dual experiment. The
important part is that there is less than one gallon of water, in
which several zebra danios lived... about August the number was
reduced to a single danio, but he seems to be living quite well in his
little setup. My experiment
is too see if I can run a tank
without water changes for a full year. So far, so good. More on this
in May 1998.
I guess the point I’m hoping to convey with this article is that we should listen to the experts, understand why they make up rules about what you can or cannot do, and then season those rules liberally with our own experience and common sense. When you’ve been keeping fish a while you begin to understand a little bit about the environment of the aquarium, and exactly how a fish will or will not thrive under different situations. Just because you read it in a book doesn’t make it correct (though reading it in several books does make it more likely to be true). I used to be frustrated by the fact that the information I got in different books frequently differed and was sometimes even contradictory... until I realized that in this hobby there are very few absolute laws. I think that’s part of the reason it is so much fun, and once you’ve gotten a little experience under your belt you can start formulating your own rules, and doling out your own opinions as advice... heck, you can even write an article about your experiences. I did.
Heather Candelaria is the owner of Crystal Aquarium, and no doubt has to answer questions about tank size like this every day.