WATERS AND HOLDING PROCEDURES
7
evident that some of the pollutants are produced by
the fishes occupying the water while others are from
outside sources.
Any materials which will readily decay we may
class as putrescible. Associated with the decay of
such materials is the utilization of the available dissolved oxygen and the production of carbon dioxide
and ammonia. The best example of this class of pollutants is excess food. Fecal material is also putrescible and has been shown by Kawamoto ( 1961 ) to result in a serious build-up of ammonia and a reduction
in dissolved oxygen.
Ammonia is considered to be a highly toxic material, and the accumulation of it in aquarium water
is undesirable. In addition to the ammonia produced
from putrescible materials ammonia is excreted by
fishes. Urea is also excreted and breaks down to form
additional ammonia. It is thus evident that ammonia
is a principal pollutant of aquarium water, and
aquarium management should involve arrangements
for disposing of it.
Under an aquarium management system where the
water level is maintained by the addition of water
without any draining of the old water there is a
gradual increase in the salt content of the water. In
addition, there is probably on the part of the fishes
some selective removal of ions and an addition of
others to the water. It is questionable if this abnormal
condition of the salt content is desirable.
When some fishes are crowded they cease to reproduce. Since water utilized by a crowded fish population wiU reduce reproduction in an uncrowded
population, it appears that fishes produce some sub-