WATER HARVESTING AND AQUACULTURE
FOR RURAL
DEVELOPMENT
INTRODUCTION
Poisons or "toxicants" are used to eliminate unwanted fish, insects and other
harmful organisms from a pond. A wide variety of poisons is available. This
manual describes some which are commonly used.
ELIMINATING UNWANTED FISH
Unwanted or "wild" fish may enter a pond through the water supply system. These
fish may be predators which eat newly stocked fingerlings, or they may compete
with fingerlings for food. In either case, they create problems for the fish
pond manager. Unwanted fish can be eliminated at harvest when a pond is drained
and dried. Poisons are effective in ponds which cannot be completely drained
and dried. Poisoning should be done with caution to avoid harmful effects to
humans, livestock, and the surrounding environment. Numerous poisons are used.
Some may be purchased in stores. Others can be found growing near the farm.
Suitable fish poisons: 1) are effective in killing unwanted species at low doses;
2) detoxify quickly in water and are not injurious to cattle and people who
may use the water; 3) leave no cumulative adverse residues; 4) are readily available
and 5) are economical to use. Table 1 describes poisons and their application
rates which may be used safely to kill fish. In Table 1, only fish killed by
(Derris root) rotenone are known to be safe for human consumption. Insufficient
information is available on the other poisons listed to make recommendations
on the safety of eating fish killed by them. DO NOT use chlorinated hydrocarbon
insecticides like endrin, dieldrin and DDT. They can make animals and people
very sick.
Figure 1: Some common fish poisons.
Table 1: Various fish poisons and their application rates in ponds.* Common
names and
comments have been supplied where possible.
Organic Methods
1. Derris root or powder
a)
10 to 20 kg of commercial powder containing 5% to 8% rotenone is applied per
hectare of water. Use the higher amount if water is greater than 15 cm deep. Mix
the powder in pails of water and splash the liquid over the pond surface.
b)
0.25 kg of dried root/100 m2 of pond surface area covered with 5 to 10 cm of
water. This equals 2.5 g of dried root/m2.
c) 1.0 kg of dried root/100 m2 in
ponds greater than 10 cm deep.
Comments:
1) Rotenone is a white
odorless substance in Derris root which inhibits respiration in fish.
2)
Poisonous effects may last from 4 to 12 days depending on the dosage used.
3) Figure 2 shows how the root is processed.
2. Bassia
latifolia (or mahua in India)
The cake remaining after oil extraction
is ground up. Powder can be thrown into puddles or broadcast over the water
surface. Ground cake can also be soaked in water overnight and spread over the
pond surface with the water it was soaked in. Apply 200 to 250 g of oil cake
made from the plant/m3 of pond water 2 weeks prior to
stocking.
Comments:
1) Poisonous effects may last from 2 to 8 days
depending on dosage used.
2) Mahua oil cake contains a water soluble
substance called saponin, which destroys red blood cells of the
fish.
3. Croton tiglium seed (croton seed)
3 to 5
g of powdered seed/m3 of pond water. Mix the powder in pails of water and splash
it on the pond surface.
4. Milletia pachycarpa
2
to 6 g of powdered root/m3 of pond water. Mix the powder in pails of water and
splash over the pond surface.
5. Barringtonia
acutangula
20 g of powdered seed/m3 of pond water. Mix the powder in
pails of water and splash over the pond surface.
Comments:
Poisonous
effects last about 2 days.
6. Randia dumetorum
12
g of powdered unripe fruit/m3 of pond water. Mix the powder in pails of water
and splash over the pond surface.
7. Walsura piscidia
(soap bark)
10 g of powdered bark/m3 of pond water. Mix the powder in
pails of water and splash over the pond surface.
8. Tobacco
waste
1.5 to 2.0 kg of waste/10 m3 of water. Tobacco waste is best
applied when water is 5 to 10 cm deep. Soak the waste overnight in water and
broadcast the waste over the pond bottom as evenly as
possible.
Comments:
Tobacco waste includes the dust, shavings, stalks
and other waste materials from cigar and cigarette factories. Nicotine is the
agent which affects fish. After decomposition, tobacco waste also serves as an
organic fertilizer.
9. Camellia seed cake (teaseed
cake)
1.5 to 2.0 kg of ground cake/10 m3 of water. Apply when water is 5
to 10 cm deep. The required amount of cake is first crushed into small pieces
and soaked in a tub or vat of water for about 24 hours. This mixture is then
broadcast evenly over the pond surface. In large ponds, the poison may be soaked
overnight in the bottom of a boat and broadcast over the pond the next
morning.
Comments:
Teaseed cake is a residue remaining after the oil
has been extracted from the seeds of certain plants in the Camellia family such
as Camellia sasangua or C. semiserrata. It is compressed into a round shape and
contains saponin (a toxin reacting in the blood).
10. Saponin (an
extract of teaseed and mahua cake)
0.5 g/m3 of pond
water.
Combined Organic and Chemical Methods
11. Teaseed cake +
Quicklime (Method 1):
a) First apply 5.25 to 6.75 kg of prepared teaseed
cake/100 m3 of pond water averaging 1 m deep.
b) Next, apply 1.5 kg of
quicklime/100 m3 of pond water.
Comments:
Quicklime is calcium oxide
(CaO) and must be used cautiously. It can burn the skin or lungs if inhaled.
Wear gloves and a mask when using it.
12. Teaseed cake + Quicklime
(Method 2):
a) First apply 15.75 to 22.50 kg of quicklime/100 m3 of pond
with an average depth of 1 m.
b) Next apply 5.25 to 6.75 kg of teaseed
cake/100 m3 of pond water.
c) Add 1.5 kg of quicklime/100 m3 a week
later.
Chemical Methods
13. Quicklime alone
a) 9 to 10.5
kg/10 m3 of water in a pond 5 to 10 cm deep. Broadcast the lime over the pond
surface.
b) 15.75 to 22.5 kg/100 m3 of water averaging 1 m
deep.
14. Hydrated lime (Ca(OH)2)
a) 55 kg/10 m3 of water in a
pond that is 5 to 10 cm deep. Broadcast the lime over the pond surface.
b)
100 kg/100 m3 water in a pond 1 m deep.
15. Sodium hypochlorite
(liquid bleach)
20 liters of bleaching solution per hectare in water 2 cm
deep.
Comments:
Chlorine is the fish killing agent.
16)
Calcium hypochlorite (swimming pool chlorine)
a) As a "rule of thumb"
apply sufficient chlorine for the fish to start dying.
b) 1.5 kg of powder
per hectare in water 2 cm deep. First dissolve the powder in water and then
broadcast over the pond surface.
Comment:
Calcium hypochlorite is a
solid powder. It can burn the lungs if inhaled. A filter mask should be worn or
breath held until the powder is safely in water.
17) Ammonium sulfate
(NH4) 2SO4
a) 10 to 20 g/m 2 to standing puddle areas.
b) 100 to 200
kg/ha to entire ponds containing water 10 cm deep.
Comments:
Ammonia
is the agent affecting fish. Increasing water pH by adding 50 to 100 g/m2 of
quicklime just before adding ammonium sulfate increases its effect.
* information in this table came from:
1) Florentino, A., J.H. Primevera and
P.L. Torres, Jr. 1983. Farming of prawns and shrimps. Extension Manual No. 5.
August, 1983. Aquaculture Department, Southeast Asian Fisheries Development
Center, Tigbauan, Iloilo, Philippines.
2) Jhingran, V.G., 1975. Fish and
Fisheries of India. Hindustan Publishing Corporation, Delhi, India.
3)
V.G. Jhingran and R.S.V. Pullin, 1985. A hatchery manual for the common, Chinese
and Indian major carps. ICLARM Studies and Reviews 11, 191 p. Asian Development
Bank, Manila, Philippines and International Center for Living Aquatic Resources
Management, Manila, Philippines.
Other plants useful in eliminating unwanted fish from ponds are listed
below. This list comes from Jhingran, 1975. Processing methods, dosage rates and
application procedures are not given.
| Indian Name
| Scientific Name
|
| safed siris
| Albizzia procera
|
| nogdona tithwan
| Artemisia vulgaris
|
| dar-hald
| Berberis aristata
|
| banalu
| Dioscorea spp.
|
| chaulmugra
| Hydnocarpus hurzee
|
| akhrot
| Juglans regia
|
| hazarmani
| Phyllanthus urinaria
|
| kuchla
| Strychnos nuxvomica
|
| sarphonka
| Tephrosia purpurea
|
| ban tambaku or gidar tambaku
| Verbasum thapsus
|
|
PROCESSING PLANT POISONS
Plant poisons are usually processed in some way to increase their
potency. Derris root is a good example. First it is dried; then soaked in water
overnight; then pounded flat. The flattened fibers are dipped and squeezed into
a pail of water until the water becomes milky (Figure 2). The milky liquid is
broadcast over the pond surface (Figure 3).
Soak the root overnight in water, then pound it
flat. Next, squeeze the root into a bucket of water until the water turns milky.
Prevent any liquid from getting into the eyes as it may burn.
Figure 2: Processing Derris root.
Figure 3: Broadcast the "milky" water over the pond
surface.
CALCULATING HOW MUCH POISON TO USE
Several factors influence
the amount of poison necessary to kill fish and the length of time the poison
remains active in the pond. The most important are water temperature, volume of
water in the pond, and the amount of decaying organic matter in the water. In
general, deep, cool water with abundant decaying matter requires more poison.
Therefore, poisoning is done in the afternoon when the water is warm. It is best
to drain most of the water from the pond before applying poison so that less
will be needed. In the case of quicklime, acidity in the pond soil affects the
amount used. For acid soils, use the high dose rate mentioned in Table
1.
A general rule to follow when poisoning puddles is to add poison until
fish start to die. For example, one puddle may require a cup of quicklime, a cup
of chlorine or a handful of mahua powder. Experience can tell a farmer how much
is required. Calculations should be made for larger volumes of water. The
following are example calculations for determining the amount of poison to use.
Refer to Table 1 for help with these problems.
Example 1:
A
farmer needs to poison his pond. He plans to stock it with fish in 3 weeks. The
pond is drained but several puddles containing fish remain on the bottom. The
farmer estimates that 200 m2 of water with an average depth of 10 cm remains.
The farmer has derris root. How much root should he use if the recommendation
(Table 1) is 0.25 kg of dried root per 100 m2 of water.?
Calculation:
200 m2 of water X 0.25 kg of dried root/100 m2 of water = 0.5 kg of dried
root
Example 2:
A rural village has a rectangular pond. The
water surface is about 48 m long and 35 m wide. The total water surface area
(length X width) is 1680 m2. The average pond depth is 1 m. Total water volume
(area x depth) is 1,680 m3. The pond has been harvested with a net, but has no
drain. Villagers want to restock the pond with new fingerlings, and want to kill
the remaining fish in the pond before restocking. Enough teaseed cake and
quicklime are available to use method 1 under item 10 in Table 1. How much of
each poison should the village use?
Calculation
A. Teaseed cake:
1,680 m3 of water X 6.0 kg teaseed cake/100 m3 of full pond = 101 kg teaseed
cake
B. Quicklime:
1,680 m3 of water X 1.5 kg quicklime/100 m3 of
full pond = 25.2 kg quicklime
Example 3:
A farmer has an
irregularly shaped pond which he can not drain completely. Remaining water is an
average of 10 cm (or 0.1 m) deep with an estimated area of 300 m2. He wants to
poison the pond with powdered croton seed. How much should he
use?
Calculation
1. Estimate the volume of water in the
pond.
a.) 0.1 m deep X 300 m2 area = 30 m3 of water.
2. From Table 1,
apply 5 g of powdered seed/m3 of water.
a.) 30 m3 of water X 5 g croton
seed/m3 of water = 150 g of seed needed
After poisoning a pond, take
precautions to prevent wild fish from entering the pond through the water inlet.
Screening or prefiltration devices are commonly used for this purpose (Figures
4, 5 and 6). Screens are typically of fine mesh (1mm square) and are reenforced
with hardware cloth for added strength.
Figure 4: Screen box and nylon mesh bag used for filtering pond inlet
water.
Figure 5: Water screening device.
Figure 6: Prefiltration method for removing unwanted fish.
TESTING TO SEE IF WATER IS SAFE FOR STOCKING NEW FISH
A
simple procedure is used to determine if a previously poisoned pond is safe for
stocking with new fingerlings (Figure 7).
Figure 7: Tie a basket to poles driven into the mud. The basket should have a
weave loose enough to let water enter but to keep fish inside, and should be at
least half submerged. Early in the morning, add about five fingerlings and let
the basket sit undisturbed. The basket can be covered to prevent fish from
jumping out.
Figure 8: Check the basket in
several hours. If the fish are still alive, the water is safe to stock. If the
fish are dead, wait a few days and test the water again with new
fingerlings.
METHODS TO ELIMINATE PREDATORY INSECTS
Young
fry and small fingerlings are especially vulnerable to predation by certain
aquatic insects which inhabit ponds virtually year-round. Ideal insecticides
kill insects without harming beneficial plankton, other natural food organisms
or fish. The safest insecticides are oil based. Oil clogs the air intake of
insects which breath at the water surface and cause them to suffocate. Other
chemical poisons containing toxic substances which affect respiration are
sometimes used. However, they may also kill beneficial food organisms or fish
and are used mostly under research conditions. A competent fisheries agent
should be consulted if such poisons are being considered for use.
Table 2: Recommendations for elimination of aquatic insects from ponds.
OIL BASED SPRAYS
1) Spray an emulsion of 56 kg of mustard or
coconut oil and 18 kg of washing soap per
hectare, 12 to 24 hours before
stocking fry.
2) Apply 0.75 l of diesel fuel per 100 m2 of pond surface
area.
Comments:
Mild wind will push the oil into a small area of the
pond causing the treatment to be ineffective. Thus, oil based poisons work best
when it is not windy.
Recommendation 1 (Table 2) was obtained from: V.G. Jhingran and R.S.V. Pullin,
1985. A hatchery manual for the common, Chinese and Indian major carps. ICLARM
Studies and Reviews 11, 191 p. Asian Development Bank, Manila, Philippines and
International Center for Living Aquatic Resources Management, Manila,
Philippines.
EDITOR'S COMMENT
Many different fish
poisons used throughout the world are not mentioned here. Readers are encouraged
to submit their methods and comments regarding locally used poisons for
inclusion in the next edition of this manual. Details regarding common and
scientific names as well as other information on finding, collecting and
processing the poisons should be included as available. Pictures would be
helpful. The following example was received from Habitat for Humanity in Zaire,
West Africa. Please follow this format when submitting
information.
Nature of Poison: A plant used to kill unwanted
fish.
Scientific Name: Tephrosia vagelli
Common Name:
information not provided
Description of Plant (tree, vine, bush,
etc.): information not provided
Method of Processing: Fresh leaves
and stems were pounded
Application to Ponds: Pounded fresh leaves
and stems were spread over the pond bottom at a rate approximately equal to 30
to 60 heaping wheel barrows full per hectare (1 to 2 barrows per 350 m2 pond)
and left for at least 3 days. Water depth in the ponds was about 3 cm.
Comments:
1) Fish and tadpoles were said to die within 2 days.
2)
The poison is believed to prevent oxygen uptake.
3) Ponds were filled and
restocked with fish 1 week after poisoning.
4) Plant leaves are oval in shape
and have short, fine, erect , white hairs, as do the seed pods. Leaves are 2 to
3 cm long and seed pods are about 5 cm long and flat.
GLOSSARY OF TERMS
emulsion - oil suspended in a watery
liquid.
fish poison/toxicant - a substance or material applied to
ponds which kills fish or insects.
fingerling - a fish weighing
from 1 to 25 g or measuring longer than 2.5 cm.
fry - recently
hatched fish weighing less than 1 g or measuring less than 2.5 cm in total
length.
insecticide - a substance used to kill
insects.
plankton - the mostly microscopic organisms (plants and
animals) suspended in the water column that serve as food for larger aquatic
animals.
Funding for this series was provided by the United
States Agency for International Development. Communications regarding this and
other technical brochures on water harvesting and aquaculture should be sent
to:
Alex Bocek, Editor
International Center for Aquaculture and Aquatic
Environments
Swingle Hall
Auburn University, Alabama 36849-5419
USA
Suzanne Gray, Illustrator
Information contained herein is available to all persons regardless of race,
color, sex or national origin.
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