POND STERILIZATION
In many cases ponds can become contaminated
with pest species which can critically impact on your commercial
production. Eels and mosquito fish are
the main culprits on the Eastern Drainage, and carp, spangled perch and
mosquito fish are the main culprits on the Western Drainage. All are problems and need to be removed from
ponds if Commercial Aquaculture is to be viable. Most of these pest fish species can breed in your ponds at
phenomenal rates. It is not uncommon to
see a 2000 square meter pond with over 50kgs of small mosquito fish in it. These fish will eat much the same food as
the yabbies or fish and consume valuable resources such as oxygen. These fish once in a pond can be very hard
to eradicate as leaving only a few in a puddle, the mud, a tyre or hollow log
will allow them to survive and then breed when you refill the pond and you will
be back to a viable population of these pests in a few months.
Most people add these species themselves
unintentionally when they fill the pond with water from storage dams. It is essential you filter your water though
a 400 micro screen to remove small fish and eggs etc. It is not uncommon for small fish, eels or eggs to be sucked up
by the pump, hurtle up the intake pipe,
go through the impeller of the pump and then through a kilometer of hose and
splash into your pond and survive.
Mosquito fish (gambusia) are masters of survival. These fish can enter ponds if water flows
over the banks, they just swim up the overflow. They can even jump vertically 1 meter and survive in shallow hot
dirty puddles when all other fish are long dead.
We use two methods of totally eliminating
these pest species. Either Hydrated
Lime or Rotenone.
Hydrated lime is a fine, dry, white powder which we purchase from our local
produce store. You need gloves to
handle it and caution on getting it on your skin or eyes etc but is relatively
safe to use if handled correctly. We
only use it to sterilize small puddles after a drain harvest. It is quite toxic to fish as it raises the
pH of the water so high that fish die very rapidly. Only small amounts of hydrated lime can be used in a yabby
pond. This form of lime acts as a
flocculent, the hydrated lime particles attract clay particles from the water
column and the whole lot becomes heavy and settles to the floor of the
pond. Too much hydrated lime can send
your pond water clear.
Rotenone is a fine powder extracted from the
roots of certain species of plants.
Rotenone is a very effective fish poison used around the world to
sterilize ponds. We apply rotenone at a
rate of 2.5 kgs/mega litre of water. We
purchase the power from a chemical firm in Sydney in 25kg bags.( Consolidated
Chemicals 02 9672 8700 ). Its relatively cheep at around $15/kg. This powder is a poison so care needs to be
employed in its handling. We use dust
masks and gloves when handling rotenone.
We add the needed amount into a 360 litre tank mix with water and use a
small efco 1 inch petrol pump to pump it out and spray it over the pond trying
to get an even distribution over the whole pond. Alternatively we will mix 2kgs of rotenone into a 20 litre bucket
of water on the bank of the pond. We
then place 100mm of this stock solution into a 10 litre bucket and then fill it
with water. We then walk around the
pond tipping in a cupful here there and everywhere into the pond. We keep doing 10 litre buckets with 100 mm
of stock solution added until all the pond is covered and all the poison is
used.
We generally reduce the pond water level by
50% before application of rotenone to reduce the amount of poison needed. Once the poison is in the pond fish will
start dying within the hour and the water will continue to kill fish for the
next 3 days. After that the poison is
biodegradable and will become less toxic on a daily basis. If used in summer within a couple of weeks
the poison will be all gone. The added
advantage of rotenone and the reason we use it is that it does not kill the
yabbies only the fish. A mixed pond of
yabbies, shrimp and fish and eels can be sterilized for the fish and eels
without the yabbies or shrimp missing a beat.
Additionally if stock drink from the poisoned water they should not be
effected and if birds eat the dead fish they should not be effected
either. Rotenone is the main fish
poison used by all the yabby farmers in this region mostly to kill eels which
destroy yabby crops. Poison is used due
to the fact that NSW Fisheries will not allow the farmers to sell eels, they
must kill them. If applied correctly
Rotenone is 100% effective at killing all fish and eels without killing your
yabbies. We ably the rotenone at a rate of 2.5kgs per mega liter of water. This is a relatively high dosage rate but
best to do it once and do it 100%. We
do all our poisoning in summer when the waters hot as its more effective at
higher temperatures at killing fish and also degrades quicker at the higher
temperatures.