WATERS AND HOLDING PROCEDURES
11
water must be low enough to permit natural processes
to maintain the water in a condition satisfactory for
fishes. Higher aquatic plants are often added to this
set-up. They increase the available oxygen and decrease the carbon dioxide, at least when they are exposed to light, and probably have the over-all effect
of making it possible to hold more fish per volume of
water. This arrangement most closely resembles natural pond conditions and is the best choice of arrangements when one seeks a good choice for display
tanks. It requires less care, may be made to look quite
natural and does not require a water supply or drain
service.
The second arrangement includes a partial change
of water daily and continuous aeration. This type of
arrangement permits holding a considerable weight of
fish in a limited space and without much special equipment. It is of value for testing toxicity of chemicals
and for the study of rapidly developing diseases such
as those caused by bacteria and some protozoans.
In the third basic type set-up the water is circulated
and filtered. This type of holding facility is of special
value where one wishes to maintain dense populations
of fish over an extended period of time and there is a
scarcity of good water of the correct temperature.
The fourth arrangement involves continuous replacement of the water by flushing. The amount of
flushing may vary considerably. Holding tanks in goldfish hatcheries may have a flush rate high enough to
give the water a change every twenty to thirty minutes,
but for aquaria where the fish are much less crowded,
a flush rate giving a complete change in twenty-four
hours is suflBcient to maintain clean water. Of course.
11
water must be low enough to permit natural processes
to maintain the water in a condition satisfactory for
fishes. Higher aquatic plants are often added to this
set-up. They increase the available oxygen and decrease the carbon dioxide, at least when they are exposed to light, and probably have the over-all effect
of making it possible to hold more fish per volume of
water. This arrangement most closely resembles natural pond conditions and is the best choice of arrangements when one seeks a good choice for display
tanks. It requires less care, may be made to look quite
natural and does not require a water supply or drain
service.
The second arrangement includes a partial change
of water daily and continuous aeration. This type of
arrangement permits holding a considerable weight of
fish in a limited space and without much special equipment. It is of value for testing toxicity of chemicals
and for the study of rapidly developing diseases such
as those caused by bacteria and some protozoans.
In the third basic type set-up the water is circulated
and filtered. This type of holding facility is of special
value where one wishes to maintain dense populations
of fish over an extended period of time and there is a
scarcity of good water of the correct temperature.
The fourth arrangement involves continuous replacement of the water by flushing. The amount of
flushing may vary considerably. Holding tanks in goldfish hatcheries may have a flush rate high enough to
give the water a change every twenty to thirty minutes,
but for aquaria where the fish are much less crowded,
a flush rate giving a complete change in twenty-four
hours is suflBcient to maintain clean water. Of course.