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Biocontrol for Fish Pond Management

The increase use of chemicals fertilizers in agriculture helped the country in achieving self sufficiency in food grain production. How ever it has also polluted the environment. The constant removal of aquatic weed by manual or mechanical methods from the fish pond weakens the productivity while the aqua culturist would like to enrich the natural status of the system. A lot of work has been done on interaction studies between crops, crops plants and weeds but reports on aquatic weeds are very few has coined the term allelopthay for the impact of secondary metabolites of one plant on other plants. Organic compounds or allelochemicals are released from all group of plants (including algae and ferns) affecting the growth and function of receiving species either by volatilization exudation or by decomposition of litter.

Methods of biocontrol: bio control may be done by using plants, animals, fungi and insects.
Plants: Ahmad (1954), Philipose (1959) has recommended use of of Salvmia, Pistin, Lemna, Eichhornia crassipes. Plants reduce the light intensity. The water surfaces of the ponds are covered by sunlight in the water and check the growth of weed.
Uses of fungus: Different species of fungus when inoculated in aquatic weed, it spreads and kills the leaves and ultimately weed is destroyed. Blooms prevent growth of weed due to high turbidity. It has been observed that presence of phytoplanktons e.g. Scenedesmus bijugatus, Chlorella pyrenoides suppresses the growth of macrophytes e.g. Eichhornia crassipes (Dharma 1985). Introduction of Ottelia to water bodies infested with Eichhornia crassipes causes anatomical and morphological changes in the latter leading to its destruction, the whole cycle of changes, degenerate and destruction takes place within three to four weeks. At the same time it was also proved that the Ottelia is harmless to other aquatic plants, animals and microbes. Beside this Ottelia could be removed easily.
Animals: Animals are used as biocontrol such as:
Birds: Kahki cambell a duck used in biocontrol. If feeds on salvinia. Insects such as Neochetina belongs to the order Coleoptera is brown color, long, elbowed antenna with three pairs of legs. Antenna folds into special grooves on the prominent snout which has mouth parts at its end. Egg hatch within seven to fourteen days. Larva makes a tunnel towards the petiole and feeds on the tissue. The tissue get rotten, leaves with feeding scars turn yellowish brown and ultimately dry.
Fishes: Fishes are the aquatic vertebrates used as biocontrol and bioindicators. Pangasisus control helminthes causing human infection, insects and gastropods of the pond. Silver carp, it checks on the development of bloom and decayed macrophytes.
Use of natural chemicals can save the environment from pollution. Major challenges before the chemist and aquacultrist is to synthesize and develop herbicides or pesticides from plants or microorganisms as these are more easily degradable. With more rapid development of biochemicals and other fast acting bio agents, bio control, which is an environmentally compatible, should be given first preference in weed management programs.

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