What if my koi are gasping?
Koi breathe by pumping water over their gills to extract
essential oxygen, which is invisibly dissolved in the pond water.
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 koi's
minimum requirement, they can adapt by coming to the surface to gulp
in air as a short-term survival strategy.
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
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 koi's 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.
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