Freshwater aquaculture

Practical 5 - Study of aquatic weeds

5.1. Floating weeds

Eichhornia sp.

• Exotic, introduced from Brazil
• Multiplies rapidly
• Present in stagnant water bodies and slow moving rivers
• Leaves broad, swollen at the base of the leaf stock, filled with air – aides in floating
• Flowers purplish pink
• On plant can give rise to 1000-1200 in 4 months
• Forms fodder
• Used for breeding gold fish and common carp

Salvinia sp.

• Ranks second among problematic weeds in India.
• Exotic, introduced from Africa
• High infestation, especially in Kerala
• Stem a delicate floating rhizome, branched and dorsally covered with oblong semi-spherical leaves
• Leaves sessile with or without stock
• Leaves arranged in three whorls- two lateral floating and third submerged
• Submerged leaves covered with minute hair-like structures
• Leave have pimple like swellings which aid in floating
• Multiplies very rapidly through spores and vegetative propagation

Azolla sp.

• Leaves lobed, scale like, thick and about 0.r5 mm long. They have no rudimentary leaves.
• Young, plants green in colour, turn brown when they become old
• Commonly found in stagnant water bodies and paddy fields
• Good food for grass carp
• Fixes nitrogen
• Reproduction vegetative

Pistia sp.

• Ranks third among floating weeds problem in India
• Tufts of leaves rise in a form of rosette at the ended of the short stem
• Has number of branching rudimentary roots
• Leaves sessile, arranged in closed spiral, forming the shape of a cup
• Multiplies by vegetative propagation
• Common in Orissa and West Bengal
• Can be biologically controlled by giant gouramy
• 20 gouramies control 1 ha Pistia in one month.