How to control aquatic weeds, predators, weed fishes and pests in coastal aquaculture.

1. Presentation on:
Control of Aquatic vegetation, Predators,
Weed animals and pests
Presenting by-
Md. Obaidul Haque (ASH1502059M)
Mahmuda Akter (BKH1502060F)
Md. Wahiduzzaman (ASH1502061M)
Dept. of Fisheries and Marine Science
Noakhali Science and Technology University
Sonapur, Noakhali-3814

2. Aquatic vegetation
Aquatic weeds are unwanted and
undesirable vegetation that reproduce and
grow in water. If left unchecked may
choke the water body posing a serious
manace to pisciculture

3. Impacts of Aquatic Weeds
 Provide shelter to predatory and weed fishes and molluscs.
 They restrict free movement of fry.
 They cause obstruction during netting.
 Limit living space for fish
 Limit plankton production
 Reduce sunlight penetration and nutrients.
 Upsets the equilibrium of physico-chemical properties of water.
 Cause imbalance in dissolved oxygen budget.
 Promote accumulation of deposits leading to siltation
 Reduce water movement, thereby limits oxygen circulation in water.
 Some weeds release toxic gases that cause fish death and add foul smell to water.

4. Aquatic vegetation Control
Control of aquatic vegetation can be subdivided into four general
categories:
(1) prevention,
(2) Manual and mechanical method,
(3) biological method, and
(4) chemical method.
Often a combination of these practices is necessary for adequate
control.

5. Aquatic vegetation Control (contd.)
1. Prevention of infestations and utilization of weeds
 Ponds or lakes should be constructed so that shallow water areas
are minimized by shaping the sides with a 3 to 1 slope (3 feet
horizontal to 1 foot vertical drop) down to a depth of at least 3
feet.
 Excessive nutrients should be prevented
 Erecting barriers or mesh filters
 The use of netting, treated with anti-fouling chemicals

6. Aquatic vegetation Control (contd.)
2. Manual and mechanical
method
 Pulling marginal plants by hand
 Small amounts of submersed plants can be
pulled out or raked by hand.
 by pulling a long chain or cable
 A hand pulled cutter, consisting of a "V"
shaped flat metal piece sharpened on the
outer edge.
 Weed cutter

7. Aquatic vegetation Control (contd.)
3. Biological method
 Herbivorous fish
e.g. Ctenopharyngodon idella;
 Other animals
e.g. Waterfowl; Ducks, geese, swans etc.

8. Aquatic vegetation Control (contd.)
4. Chemical method
Herbicides may be used to control
aquatic weeds but control may
vary due to such factors as
susceptibility of the aquatic
weed(s) to the herbicide, stage of
growth, rate of application; and
the time of application. Some
herbicides may also cause injury
to fish if not applied properly.

9. Selection of control method
The selection of the method of control has naturally to be based on
the type and density of the infestations, the nature of the farms, and
the species that is cultured. Similarly, it is necessary to select the
most appropriate time for treatment to get best results. Control
measures are more effective if applied at the most vulnerable period
in the life history of the weed, which is often the period of intensive
production of reproductory units.

10. Control of predators
1. Predatory fish
 Complete removal can be accomplished by totally
draining the body of water or by chemical treatment.
 Chemical removal of fish populations is a widely
practiced management procedure applied to ponds and
lakes used for recreation or for aquaculture.

11. Control of predators (contd.)
2. Birds
 Small ponds and raceways can often be
covered with nets or wire-mesh.
 Devices like flash guns, sirens, klaxon horns,
gongs, scarecrows, bamboo rattles and bells
have all been tried with initial success.
 In small nursery pond in Southeast Asia,
farmers sometimes run lines of string on poles
set in the pond and attach bright colored pieces
of cloth or metal to the string to scare birds.

12. Control of predators (contd.)
3. Mammals
 The best control methods involve trapping (when legal).
 Other nonchemical methods include reducing the food supply,
installing protective barriers, and shooting. Chemical control
may consist of the use of repellents, fumigants, and baits.

13. Control of predators (contd.)
4. Reptiles
 There are no pesticides registered for the control of
aquatic reptiles. Control can usually be
accomplished by trapping or shooting.

14. Control of predators (contd.)
5. Amphibians
Can be prevented from entering farms with proper
fencing and by keeping the pond banks and
surrounding areas free from dense growths of
vegetation.

15. Control of weed animals
1. Weed fish
 Use of filtering device
 Selective fishing or selective toxins will have to be used.

16. Control of weed animals (contd.)
2. Snails
 The application of 12-15 kg/ha of nicotine (commercial tobacco dust)
or 15-18 kg/ha of saponin on the pond bottom after drainage of the
pond is reported to be effective in controlling snails in coastal ponds
(Tang, 1967).
 Manual or mechanical removal of snails can also be effective if
properly done after the ponds are drained.
 When the pond cannot be drained, application of Bayluscide (5,2-
dichloro-4f-nitro-salicylicaniline-ethanolamine), at a concentration of 3
ppm in the pond water, has been suggested ( Tang, 19670).

17. Control of Pests
1. Polychaete worms
 Drainage of ponds seldom helps to eradicate the worms.
 Tang (1967) reported that 2 ppm nicotine or 3 ppm
Bayluscide are effective.
 Application of technical Y-BHC at a concentration of 0.08-
0.1 ppm ( Tang and Chen, 1959).

18. Control of Pests (contd.)
2. Crabs
 Jordan (1957) reported that repeated fortnightly spraying
with a 10% suspension of technical BHC (containing
6.5% gamma isomer) was effective in controlling
Sesarma and Sarmatium species.
 ASEAN (1978) reported the use of the insecticide
‘Sevin’.
 Application of calcium carbide in crab holes.
 Tobacco dust and several other toxic materials and
insecticides have also been used as contact poisons to kill
crabs.

19. Control of Pests (contd.)
3. Burrowing shrimp
 The methods adopted for controlling crabs can be
used for killing this.
 Special trigger-type traps have also been found to
be useful in catching them.

20. Control of Pests (contd.)
4. Musk rats (Ondatra)
Suggested ways of controlling them are
capture with traps and trap-nets or by
shooting.

21. Control of Pests (contd.)
5. Fouling organisms
 Regular cleaning and drying is essential to keep these in
good condition.
 Greater use of cement concrete to build water control
structure.

22. References
T.V.R Pillay, Aquaculture principles and practices, First Indian reprint 2005, PP-216-227.