Freshwater aquaculture (2+1)

Practical 5 - Study of aquatic weeds

Introduction

• Weed infestation is a problem in aquaculture, particularly in earthen ponds
• Control is easier in small ponds but not in large ponds
• Adds substantially to operational cost

Growth of weeds depends on

• Depth of water
• Type of bottom sediments
• Fertility and clarity of water
• Climatic condition

Disadvantages of weeds

• Hinder navigation
• Increase sedimentation
• Decrease plankton production
• Harbour predatory and weed fish
• Harbour insects
• Water loss through transpiration
• Hinder netting operation

Advantages of weeds

• Increase DO
• Reduce CO₂
• Egg collectors – Common carp, gold fish etc.
• Food for some fish
• Ornamental in aquaria
• Control of excess algal blooms

Classification of weeds
Weeds are classified based on the area in which they are present in ponds as follows

• Floating weeds: Unattached free floating, leave above surface and roots dangling down
• Submerged: Completely submerged in water, rooted at the bottom, some without roots
• Emergent: rooted at the bottom, all or some part of the leaves above water
• Marginal: found on the shore line rooted in water logged areas
• Filamentous algae: form mats or scums in pond