|Fortunately, compared to other fish species,
koi do not require an especially high level
of dissolved oxygen (DO) which makes them relatively
undemanding in this area. Even when, through
whatever reason, DO does fall below a kois
minimum requirement, they can adapt by coming
to the surface to gulp in air as a short-term
survival strategy. However, this is extremely
stressful for fish and if you are witness to
such an extreme change in behaviour the alarm
bells should start ringing.
As is the case
when confronted by any pond or koi-related problem,
a responsible koi keeper should approach it
in 2 ways and ask a couple of questions.
- How can I remedy the problem and avoid
stressing the fish any further?
- What can I learn from this experience
as far as what caused it and how can I prevent
it from happening again?
A gasping response in fish will not necessarily
always be caused by an unhealthy drop in DO
but may also be behaviour shown by fish that
is not getting sufficient oxygen to its tissues
for another reason.
Besides a drop in DO (which is the most likely
cause of gasping behaviour) another cause could
be that the koi are suffering from poor water
quality, specifically nitrite toxicity.
If for some reason, toxic nitrite is not
being broken down and detoxified effectively
by a biofilter, then it will cause a build up
of nitrite within a kois blood and tissues.
When nitrite reacts with the oxygen-carrying
haemoglobin within the blood, it forms a stable
non-oxygen carrying form of haemoglobin, which
will in turn cause the fish to gasp.
For this reason, in addition to adding extra
aeration it would be prudent to carry out a
water test to identify if the cause of the problem
is associated with a water quality problem.
Other more common causes of gasping in fish
can usually quite simply be identified and easily
rectified. These include:
Yes, occasionally we can suffer from hot
weather in the UK. As water warms up, its ability
to hold DO decreases and yet a fishs oxygen
requirements increase. The DO requirements of
other organisms in the pond such as bacteria
and other aquatic creepy crawlies also increase.
If a pond is running close to a comfortable
oxygen level prior to such a hot spell then
when the water temperature rises, the double
whammy affect described above can leave koi
and the pond environment oxygen-deficient.
A well-planted pond in full sunlight is a
real asset as a natural source of oxygen as
the plants produce far more oxygen in photosynthesis
than they use in respiration. However, at night,
the same plants will still be using oxygen and
will not be releasing any oxygen through photosynthesis.
This will cause a drop in pond DO causing the
fish to gasp first thing in the morning as a
result of a phenomenon called dawn depletion.
A remedy for this is to thin out excessive submerged
plant growth and improve aeration or circulation
within the pond.
Some pond medications when added to the water
can cause quite a severe drop in DO through
chemical reaction. Medication may also reduce
DO through adverse interaction with other pond
life. Extra aeration should be added during
any course of treatment or medication as a precaution
and extra care should be taken after the use
of an algicide. Dead algal matter will put an
extra burden on the oxygen budget within the
pond as it is broken down by bacteria.
This cause of low DO may sound obvious but
a blocked pump or filter may cause problems
by stealth where a gradual, almost unnoticeable
drop in turnover occurs. This will have a knock-on
adverse effect on DO levels.
Regular flushing and maintenance of filter
media and pump pre-filters will keep this from
becoming a real problem. Blockages are more
likely to be an issue in the warmer months when
excessive algae growth is experienced.
It is reassuring to know that a pond can
not be over-aerated and through the many different
means and devices available today, barring accidents,
low DO should not be a problem in a well managed
Filtration will nearly always benefit from
the addition of extra aeration which in turn
will lead to better water quality. Venturis,
air stones, micro-bubblers, and even air domes
fitted to bottom drains allow easy, effective
and efficient aeration and are a must for any
serious koi keeper.
pond oxygen-carrying water fish koi "extra
aeration" nitrite reason gasping medication
"water quality" air filter plants bacteria