Page 68 - Koi Net - On-Line Koi Magazine - Issue 94

Then they performed an awesome experiment! They What does this mean for our Koi hobby?
sacrificed a few carp from these groups and placed the
gills in airtight rooms with radiologically labelled
Ammonia and nitrite, and looked at how much nitrogen
gas N was produced in 150 minutes. Control fish that
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were not fed produced 26µMol, while the gills of fed fish
produced 303µMol. Because a lot of oxygen is always
present on the gills, the question was asked whether this
was due to anaerobic bacteria (without oxygen growing)
or by aerobic bacteria (with oxygen). As it turns out,
without the presence of oxygen, no nitrogen gas was
produced by the gills (the bacteria present on them).
This result implies that there must be a cooperation
between bacteria that oxidise the Ammonia (making
nitrite) and the denitrifying bacteria (that turn nitrite into
N gas). Up to this point it has always been assumed
²
that the presence of oxygen prevents denitrification.
Then they demonstrate with complicated techniques
that I will not be explaining now, which bacteria they
found on the gills. They have found groups of bacteria
that include Nitrosomonas-like (Ammonia oxidising) and
the protein (NirS) that is in bacteria that break down
Nitrite into N gas. The different types of bacteria were
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grouped together around the blood vessels in the gills.
The authors further claim to have found these to be
intracellular. Intracellular means literally in the cell, so in
the fish cell, which of course would be a sensational
find. I must honestly say that I find the evidence in this
article that they are inside the cell very limited. The fact
that these bacteria are co-localised, so found together
on the gills around the blood vessels and produce
nitrogen gas, that evidence looks solid.
Fluorescence in situ hybridisation
(FISH) on gills of common carp. A B chambers, and anammox part will be there.
(A) Phase contrast image with
visible bacterial clusters
(arrows) surrounding a blood
vessel ( ).
*
(B) FISH using eubmix (Eub I, II,
III, labelled with Cy3)
targeting all bacteria. Scale
bar represents 10 µm.
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I expect that this effect has also played a role in all
previous studies, so the measured and presented value
is lower than the actual secreted Ammonia (TAN) value.
The percentage excretion from the food will therefore
have actually been somewhat higher. The values that
have been measured as excretion are still the amount of
Ammonia that your filter must process, so that does not
change much. You can therefore influence the total
amount of Ammonia formed by this way of feeding. If
you do decide to give a certain amount per day, spread
it as much as possible over the day (and night). If the
effect from the last article takes place in our ponds then
we can use this. Just provide the food a bit every hour
with a feeding machine in the summer when the amount
of feed rises. This gives you the best growth with the
least amount of food and the Ammonia excretion gets
fewer high peaks but remains more constant. The fish
can handle this better and so can your filter. Because if
your filter bacteria are permanently supplied with a
small amount of food (Ammonia), they will not be
hungry in between and will function best.
My question was: Where does the nitrogen in our ponds
go to? Well, I have not been able to find solid evidence
for which process in our ponds is precisely the most
responsible for removing the nitrogen from all our
ponds. Probably denitrification. It is almost certainly a
combination of the processes mentioned. Depending
on your pond and filter setup and management, one or
a few of these processes will take place in your pond.
Gasification via the gill bacteria population will help for
the removal of nitrogen from the pond, but also
heterotrophic growth via cleaning of sedimentation
Denitrification should certainly take place if you do not
want to continue to build up the nitrate. I think that in
successful ponds in particular the colonies with
Ammonia oxidising and denitrifying bacteria together in
the filter can form the same mini-colonies and
cooperation as described in the last article on the gills.
This would in fact explain that in our filters, despite the
usually too thin biofilm layer for anammox, in addition to
nitrite and nitrate, N gas is also made and if this
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evaporates away you can reduce the nitrogen content
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