weeds & planktons and its control
TRANSCRIPT
WEEDS & PLANKTONS AND ITS CONTROL
Balwant SinghAmbreen Wahidy
Babasaheb Bhimrao Ambedkar UniversityLucknow-226025 INDIA
Aquatic weeds are the undesirable plants that grow inwater and are more harmful than beneficial for fish culture.Excessive growth of aquatic vegetation prevent effectiveutilisation of water and reduces productivity. Depending on theirhabitats, weeds have been classified into the following groups.
1. Floating plants:
these weeds have there their leaves freelyfloating on the surface of water, and roots hanging underneath.They are profusely found in wind protected ponds and areharmful as they shade the pond, e.g., Eichhornia, Pisita, Lemna,Azolla, Wolffia etc.
AQUATIC WEEDS AND THEIR CONTROL
2. Emergent weeds:
these are surface plants which are rooted in the bottomof the ponds, but their levels on the water surface or rise above the waterlevel. They prefer shallow parts and shores of the ponds, e.g., nymphea(Lotus), nelumbium, nymphoides.
3. Submerged weeds:
these plants grow under the water surface and mayor may not be rooted submerged weeds are Hydrilla, Najas, Vallisneria,Potamogeton etc. Rootless plants are Ceratophyllum, utricularia etc.
4. Marginal weeds:
these plants grow along the shore line of the pond e.g.,Typha, Cyperus, Colocasia, Ipomoea, sagittaria etc.
5. Mats or scums:
these formed by filamentous algae and chlamydomonas
e.g., spirogyra, pithophora etc.
SUBMERGED WEED
Hydrilla
Floating plant
Pistia
Emergent Weed
Nelumbium
MARGINAL WEED
Cyprus
Aquatic weeds are harmful as theyconsume nutrients of the pond and obstructnetting operations. They check free movementof the fish and cause oxygen depletion andaccumulation of carbon-dioxide. Gases likehydrogen sulphide and methane are formedwhich are harmful to the fish. Algal bloomschoke the gills and spoil the water on rotting.
DISADVANTAGES OF WEEDS
aquatic plants, when in limitedquantity are useful and necessary for theecology of the pond. They form naturalfood of many species of fish, and fertilizethe pond when decayed. They reduceturbidity and provide spawning beds forfishes.
Advantage of aquatic weeds
The aquatic weeds can be kept in check bythree methods:
1. Mechanical
2. Chemical
3. Biological
WEED CONTROL
Mechanical removal of weeds by employing human labor or bymachines is the most satisfactory method. In India, where labour is cheap,manual labour is often employed. Periodical removal of aquatic plants byhand picking, uprooting or cutting, keeps them in check. During the recentyear, power lifts or diesel operated machines have been used for eradicatingdense rooted vegetation.
several weeds like water hyacinth, Pistia, Salvinia, Azola, and lemnaare the most common floating weeds in ponds and lakes. Complete removalof these weeds by manual labour, drying and burning it up,is considered themost effective method of eradication it. Good manure can be obtain bycomposting the weed in pits. However, these plant have to be removablebefore they emerge again.
WEED CONTROL BY MANUAL AND MECHANICAL METHODS
Several chemical weedicides are now available for the
control of aquatic weeds, but they have to be used carefully toprevent adverse effect on the fishes in water . The chemical is tobe selected and used in such a way that:
1. It should be cheap and easily available.
2. Non-toxic to fish and man.
3. Should not pullute the water and
4. Should not involve the use of special and costly equipment.
CHEMICAL CONTROL
Of all the floating weeds, the water hyacinth,Eichhornia crassipes, is the most common and ofgreatest nuisance value. It can be successfullycontrolled by the chemical 2,4-dichlorophenoxy aceticacid (2,4-D). This chemical is applied at the rate of 4.5-6.5 kg/ha, and has little harmful effect on fish.
3.5 kg of chloroxone in 500-1000 liter of watercan be sprayed on an acre of water. This chemical killsthe plants in 2-3 weeks but is harmless to fish andoperator.
FLOATING WEEDS
Plants like typha, colocasia, sagittaria and grassesgrow alow along the pond margin and harbourpredatory insects. Although the most effective methodis to cut them by manual labour. They can be controlledby chemical weedicides. Young cyperus and colocasiaare totally killed with 1-1.5% aqueous solution oftraficides-80 a solution of 2,4-D sodium salt (3-4%) with0.25% surf.
MARGINAL WEEDS
Water lilies and lotus are the common rootedplants with leaves emerging on the surface. Pullingthem out with manual labour or surface treatment withchemicals is of little use in eradicating them. Use oftraficde-80 is reported to be effective in controllingNelumbo.
EMERGENT WEEDS
Submerged plants like Hydrilla, Vallisneria,Potamogeton, naja and ceratophyllum are mosttrouble-some, and there removal by manual labour istedicus and costly. The submerged weeds are kilied ifthe water is made is made turbid for a long tirne.Copper sulphate in combination with ammonium salt isalso found to be effective.
SUBMERGE WEEDS
The filamentous algae rarely become a nuisance,but sumtimes Spirogyra and pythopthora formextensive mats. Sodium arsenite is effective in killingthem especially in warm weather. They can beeradicated by treatment with copper sulphate.Simazine at a small dose of 0.5-1.0 ppm is also effectivein controlling Microcystis.
ALGAL BLOOMS AND FILAMENTOUS ALGAE
Several type of weeds can be kept under controlwith the help of a few species of herbivorous fishessuch as the Ctenopharyngodon idella and cyprinumcarpio. It has been found that advanced fry andfingerlings consume wolffia. Advanced fingerlings,juverniles, lemna, azolla and salvinia. The fish is alsoreported to feed on vallisneria and potomogeton.
Inorganic fertilizer mixed with 10%, sodiumnitrate are used for controling submerged weeds likeNajas.
BIOLOGICAL CONTROLE
Plankton include the free floating minute plants andanimal organisms, that have very feeble locomotory organsand simpaly drift with the water currents. On the bassis ofsize. Plankton are divided in to three kind: macro-, micro-,and nanno- planktons. The macro-plankton includeorganisms that are large than 3 mm in size, and visible withthe naked eye, such as larvae, mysids, salpa etc. The largestforms are also called megaloplanktons. The microplanktonare form below 3 mm in size, while the forms less then then60 micra in diameter are called nannoplanktons. Theselatter can be collected by the finest mesh cloth andcomprises of diatoms, protozoans and bacteria.
PLANKTON & ITS ROLE IN FISHERIES
PHYTOPLANKTON
Plankton are also classified as phytoplankton. Ofthese the phytoplankton includes organisms withchlorophyll such as microcystis, volvox etc. as well asnon-photosynthetic plants like bacteria and fungi. Itinclude all the passivelly floating microscopic plants,diatoms and dinoflagellates. The zooplankton are minutanimals like the protozoans (radiolaria, forminifer)rotifer, crustaceans like the copepods, ostracoda,amphipods, worm, eggs and larvae. The plankton maybe of temporary nature. These consist of planktoniceggs and are abundant during certain season only,planktons found throughout the year are calledpermanent or holoplankton.
Cont….
Plnkton show a number of adaptation to keep themfloating in the surface water, and prevent sinking. Forexample, the cell is relatively large and become bladder-likefilled with alight fluid.
Sesonal qualitative and quantitative fluctuatoin occursin the plankton of pond. In fresh water ponds of utterpradesh peaks of plankton are reported to occur duringspring and monsoonwhile slake period is observed duringsummer months.a bimodial pattern of plankton productionhas been reported in various ponds,the monsoon peakconsisting mostly of pytoplancton while the winter peakconsists mainly of zooplankton.
Cont…
ZOOPLANKTON
Plankton are used as food by a large number of animal speciesincluding fishthey can also be used as food by man.
The phytoplankton are the producers in the aquatic foodchainand are found in aii waters upto the depth where lightcan penetrate.
Certain species of fish feed on phytoplankton such asmulticellular and unicelluar algae,and directly depend on themfor for their existance.
Zooplanktons feed on phytoplanktons and are primaryconsumers in the food chain.The planktons form the basic foodfor all fish species,directly or indirectly.
PLANKTON AS FOOD
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