Principles of Keeping Good Aquariums

Keeping fish is an endlessly fascinating andsolubility of oxygen, and thus the lower the fish
absorbing hobby. The size and shape of tanks iscapacity. The following estimates assume an
discussed below, as is the fish capacity of tanks.average temperature of about 75 degrees F for
Aquaria for decorative purposes should be madetropical and about 60 degrees F for cold-water
from clear glass, without the irregularities andfishes. They assume no aeration, and they also
flaws frequent in ordinary window glass, and theassume that young fishes and small fishes, even
glass should be thicker than window glass in anythough adult, use more oxygen per unit of body
but the very smallest tanks.weight than do larger fish.
Shape and Size of TanksThis is in line with such experimental details as are
Aquaria should be as shallow as possible, since theavailable, though they are scanty, and with general
surface of water exposed to the air is the mostexperience. They are not based on the "gallon" or
important factor in determining the number of"inch of fish" rules, which give various estimates
fishes they can safely hold. However, a veryof the number of inches of fish per gallon which
shallow tank is an eyesore, and a compromise ismay be placed in tanks, because this type of
always made between biological and artisticcomputation is clearly fallacious and is not in line
requirements.with either the practice or the experience of
Many prefer a "double cube" type of construction,observant aquarists.
with the tank twice as long as it is wide and high,The general basis of the estimates is as follows. It
i.e., 24 X 12 X 12 inches. This tank is still ratheris assumed that, age and activity apart, the same
shallow for the full growth of plants and looksvolume or weight of fish uses about the same
better if the height is somewhat increased, soamount of oxygen per minute, whether it
that a common variation is 24 X 12 X 14 or evencomprises a hundred small fishes or one big fish.
24 X 12 X 16 inches.However, small fishes and young fishes are usually
Fish Capacity of Tanksmore active and young fishes are still rapidly
Until recently it was believed that the exchange ofgrowing. They therefore consume more oxygen
carbon dioxide and oxygen between fish andweight for weight, and allowance is made for this
plants, taking place directly through the water,to the extent that 1 ounce of 1-1/2 inch fishes is
was more important than is really the case. In aallowed five times the oxygen consumption of 1
crowded tank, with plants in a good light, thisounce of 2-1/2 inch fishes, and each ounce of
interaction matters considerably, and the same6-inch fishes is allowed rather less oxygen than
tank is often in a poor state at night.that of 2-1/2 inchers.
With a tank not unduly crowded, either with fishThe base line is the 2-1/2 inch tropical fish, which
or with plants, the exchange of gases betweenis allowed 20 square inches of surface area - a
the air and water is more important than anygenerous allowance - and all estimates should be
other factor. This is why the surface area of thedivided by 3 for cold-water fishes and by 6 for
tank counts for so much and why, in practically allfancy goldfish varieties. The 20-square-inch
circumstances, the influence of plants may beallowance is intended to permit further growth
ignored when fish capacity is considered from aand good health. The fishes would not be
respiratory point of view.expected to show distress if their numbers were
We compute fish capacity from surface area, anddoubled, but they would not flourish so well.
we may modify this by including the effects ofFollowing these few simple principles, an attractive
temperature, water movement, and various otherand long-lasting aquarium can easily be set up.
factors. The warmer the water, the lower the