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For fresh Water Fish Culture & Inland
Advantages of Aquatic Weeds
• Weeds are aquatic plants grows near, in or under water bodies. Weeds when present in a
water body have some advantages as well as disadvantages and when present abundantly in a
fish cultured ponds they pose threat to fish culture.. We found diversity as far as the type and
habitat of weeds are concerned.
Advantages of weeds are as follows.
• During day time aquatic weeds produce oxygen during photosynthesis.
• They serve as food for many aquatic organisms.
• They are autotrophs and hence serve very important starting link of ecology of a water body.
• They serve as protective cover for an organism [Even a fish] from enemy.
• Some weeds absorb heavy metals form water bodies and hence serve as anti-pollutants for
water bodies making the water bodies free from pollutants.
Disadvantages of Aquatic Weeds
As far as fisheries is concerned disadvantages of the weeds are to be considered, for weeds when
present in fish ponds poses threat to the fish production for the following reasons
• 1] Blocking Sunlight: - Sunlight plays important role in living world. It is
necessary for each and every living thing. However weeds when present in
fish ponds blocks the sunlight to reach in a pond water and thereby entire flora and in turn fauna
gets affected for want of sunlight and it has got adverse effects on the ecology of a water body.
Sunlight is important in the plankton production which is a natural and primary food of fish.
The plankton, natural fish food production is adversely affected which thereby may
results in mortality of fish, so also sunlight is also necessary for the growth of fish, which gets
adversely affected in the absence of sunlight. It is one of the reasons for which weeds must be
removed from the fish ponds.
2] Production of carbon dioxide: Weeds though during daytime produce oxygen which is
needed for the fish culture, however during night they produce carbon dioxide during respiration
which gets dissolved in the pond water. Excessive carbon dioxide may results in the higher
mortality rate of the fish depleting oxygen levels of water body, and also it create competition of
oxygen between weeds and fish which is dangerous for the fish cultured
3] Decomposition of weeds: -Parts like leaves, branches etc. of submerged, emergent
and floating weeds or when entire weed die it decomposes in the pond water. During
decomposition process foul smelling gases like hydrogen sulphide, ammonia etc. are produced.
These gases are also harmful to fish culture which is being carried out in a pond. Fish being
biological indicator, these gases affects fish at once may resulting in high mortality of fish seeds.
4] Enemy Hideout: - Weeds provides excellent hiding place for the fish enemies like
frog’s snakes and insects. All types of weeds weather marginal, submerged or free floating
provides space to the enemies of fish. Harmful insects like Anisop, Ranatra, Belostoma etc. may
attacks fish and may feed on the flesh of it or may drink blood of fish.
Snakes and frogs and other carnivorous aquatic species feeds on fish which may
results in less fish production.
5] Space: Weeds in a pond eats up the space in ponds and therefore as a result there
is less space is left for the fish movement. Lack of space for free movement may results in stunted
growth of fish and also may results in stress on fish causing diseases or mortality of fish, so also it
interferes in netting operations. If the fish seed is small then there is every possibility of fish seed
mortality, secondly one is unable to detect fish seeds in the heap of weeds and again possibilities
of mortality of fish seeds. Excessive weeds or algal blooms endanger fish seed life for it may get
settled on the gills of fish seeds resulting mortality of fish seeds
• 6] Interference in netting: - Weeds when present in ponds interfere in netting operations and
thereby making it difficult to catch fish. It also hampers the regular observations on growth and
health of fish population, which is one of the important aspects of culture fisheries.
Classification of Aquatic Weeds
• We found varieties of weeds in a water body. Weeds practically invaded the water bodies at
all the levels of water bodies and according to their habitat weeds are classified as given
• These are found along the margins of the fresh water bodies and include Typha, Ipomoea
etc. In case of typha the rhizome of it is having horizontal scales and it grows along the
margins of water body vertical leaves grown at the distance along the entire length of
rhizome. Marginal weeds provide cover for the fish enemies and also harmful insects. Typha
is one of commonly found weed along the margins of a neglected water bodies
• Ipomoea is also one of the commonest marginal weed found along the margins of a water
bodies. It is having alternate leaves and violet flowers.
FREE FLOATING AQUATIC WEEDS
Free floating weeds are found in fresh water ponds, lakes and or ditches. These are
called as free floating weeds for their roots hangs in the water body and not attached to the
substratum and therefore this type of weed floats freely in a given water body. The common
example of this type of weed is pistia, azolla, Lemna etc. these weeds have special modifications
for floating in the water bodies.
• In case of pistia roots are adventitious and clusters of leaves arise above the roots. The leaves
of the weed are compactly packed and appears like that of cabbage and hence it is also
known as water cabbage. The rosette of leaves remains open horizontaly during the day and
is closed during the night.
• In case of azolla the roots are adventitious, however the leaf is having two lobes one helps
the weed for floating since it is full of air and this lobe is inside the water the other above the
• Submerged weeds: - Submerged weeds are found in fresh water ponds, lakes and or ditches.
These types of weeds grow under water, if rooted the roots grows in the substratum for
holding the weed in the water body. These are of two types one with roots others without
roots the examples of rooted weeds are Vallisneria, Hydrilla, Ottelia ,Ceratophyllum and
• In case of vallisneria it grows in the water attached to the substratum firmly with the
adventitious roots. Leaves are like that of like sugarcane plant. The entire weed is coated with
the mucous which protects the weed from dying or decomposition.
• Ottelia:- It is found in fresh water lakes or damp places Stolon [ Stem] branched, leaves
alternate or opposite on the stolon.
• Utricularia:- It is found in fresh water bodies or in wet soil. They are carnivorous plants and
capture their prey in their bladder traps. These plants can feed on fish fry’s and are therefore
harmful for fish culture.
• Ceratophyllum is a submerged, free-floating aquatic plant, found in fresh water ponds, lakes, or
ditches. It is rooted in mud at the bottom of the water. The stems with numerous side shoots
making a single specimen appear as a large, bushy mass. The leaves are produced in whorls of six to
twelve, simple, or forked into two to eight thread-like segments edged with spiny teeth. Aquatic
weed with separate male and female flowers produced on the same plant. The flowers are small,
greenish-brown. The fruit is a small.
• Hydrilla It is rooted aquatic weed found in fresh water bodies. Stem is weak and leaves are
arranged alternately, however at the apex the phyllotaxy i.e. the arrangement of leaves is in whorls.
• Emergent weeds are found in fresh water ponds, lakes and or ditches. These weeds are attached to
the substratum inside water and emerge out of water. Lotus is one of the common examples of the
emergent weeds other examples are Nymphea and Nymphoides.
• Lotus is one of the best examples of emergent aquatic weeds. It is rooted in mud at the bottom of
the water the stem arises out of water. Leaves are big roundish and coated with waxy substance
hence the leaves cannot get wet. Flowers are big and rubbery; the entire weed is coated with
mucous to protect it in the water.