FROM PLANT TO POISON - IDL-BNC @ IDRC

AJ?er betng soaked in waterfor hua
houn-, tbe ptscicide is spread over
shn’mpponds. The substance 1eaue.s
no toxic residue.
Five plants were ultimately chosen
for fïeld testing on shrimp farms.
Researchers extracted powders from
the plants and dried leaf preparxions
and experimented with different
methods of applying them as pisci-
cides. They assessed fish mortality by
species along with yields and eco-
nomic returns Their findings vfere
compared to tbe results of using tea
seed as a fish poison.
A fat-growing shrub called Mueseu
ramentaceawas the final plant to be
selected for further testing and evalua-
tion. “One of “UT biggest challenges
was trying to determine the active
ingredient of the plant,” says Prof
Pichaet. It took a lot of investigation
to learn the st”lct”*e of the chemical
compound of tbe plant” The detective
work revealed that the plant’s key
active ingredient was saponin, which
selectively kills fish without affecting
other organisms in the water.
Dubbed Swimtop by researchers,
the pisciùde is made by drying and
crushing the leaves of the Maesea
ramentaceashmb. The resulting
powder is packaged in small enve-
lapes resembling tea bags and then
suspended on the water’s surface. The
piscicide, absorbed through a fish’s
gills, breaks down red blood cells.
‘Ibe fish is thus deprived of oxygen
and dia. Shrimp remain unaffected
because they are physiologically
different from fish.
Only a small quantity of leaves is
required to kil1 fish (2Og of dry leaf
powder per ton of water). At doses
lower than this, Swimtop temporarily
stuns the tîsh, making them casier to
harvest. In one field tria1 in the village
of Ko+ the fish were even caught
with bare hands.
The piscicide is currently undergo
ing tests to determine ifs effects on
humans and other mammals. ?he
analysis is being done according to
the OECD Guidelines for the Testing
of Chemicals. Dr Sam Kacew of the
Department of Pharmacology at the
University of Ottawa, is supervising
these tests. He says the early studies
show that in high concentrations,
Swimtop has no apparent toxic effect
on mammals.
The piscicide has been well received
by shrimp and fsh farmers. It is inox-
pensive and the plant from which it is
derived is easily available and an be
mass cultivated. “You ca” take a cut-
ting, stick it in the ground and it will
grow into a tree, ” says Towers. More-
“ver, it leaves no toxic residue SO the
fish an be eaten without harm.
Swimtop also breaks down quickly SO
treated ponds an be restocked with
fish within 72 heurs.
Researchers bave applied for patents
in both Thailand and Canada. They
bave also prepared a business plan
and bave held preliminary discussions
with several companies about the
commercial manufacture of Swimtop.
If successful, seven years of research
into an effective piscicide may lad to
pd3.S.
Ron Stanaitis in Thatland
Kil
Professa Pichaet Wiriyachitia
Research Centre for Natural
PICdUCt.5
Faculty of Pharmacy
Chiang Mai University
Chiang Mai 5ooO2
Thailand
Tel and Fax: (053) 217 288
Dr Neil Towers
Department of Biology
University of British Columbia
Vancouver, British Columbia
canada V6T lW5
Tel: (604) 822-3338
Dr. Sam Kacew
Department of Pharmacology
University of Ottawa
451 Smyth Road
Ottawa, Ontario
Canada KlH 8M5
Tel: (613) 787-6531
Fax: (613) 731-8949
IDRC Repens, January 1993 19