Aquatic weeds become menacing to fish cultivation when their growth is excessive. Excessive vegetation of all categories is harmful, be it emergent, floating or submerged type of weed. The disadvantages caused are many. Control of weeds is an important part of pond management. In this topic different types of aquatic weeds with example and their advantages, disadvantages and their control measures are described.
Keywords: Aquatic weeds; Types; Advantages; Disadvantages; Control
Weeds are unwanted aquatic plants of uncontrolled growth. Aquatic plants are the primary producers of the aquatic ecosystem. They help the fishes in providing food, oxygen, shelter etc. The presence of these unwanted and undesirable aquatic plants certainly pose threat to the productive potential of the aquatic body. In fact, the presence of certain aquatic plants is frequently desirable in fish ponds. Any slackness in controlling their excessive growth diminishes productivity of the water body by utilizing the nutrients or check the penetration of sunlight by shading may lead to either super saturation or depletion of O2. Aquatic weeds provide harboring place to predatory and weed fishes are profuse feeders and prolific breeders and over populate themselves. These factors limit the availability of foods. Gases like H2S and CH4 are formed which are harmful to fishes. On the other hand, presence of aquatic weeds in small numbers is necessary because they form natural food for many fishes. They form good fertilizers in the pond when decayed.
Over 140 species of plants have been reported to act as aquatic weeds both within and around various kinds of aquatic bodies in India. The states comprising West Bengal, Odisha, Bihar, Assam, Tripura and Manipur have the maximum incidence of weed infestation ranging from 40-70%, whereas in other states it may range between 20-50% (Philipose, 1968) [1-5].Over 140 species of plants have been reported to act as aquatic weeds both within and around various kinds of aquatic bodies in India. The states comprising West Bengal, Odisha, Bihar, Assam, Tripura and Manipur have the maximum incidence of weed infestation ranging from 40-70%, whereas in other states it may range between 20-50% (Philipose, 1968) [1-5].
They are not attached to the pond bottom rather float upon
the surface. Sometimes they profusely grow and shade the pond,
so are harmful to the fish in many ways. e.g. Azolla, Pistia, Wolfia,
Lemna etc (Figure 7-9).
i. Biological control through herbivorous fishes are -
Osphronemus gorannmi, Ctenopharyngodon idella (Grass carp),
Puntius javonicus (Tawes), Tilapia mossambica, Chanos chanos
(Milk fish) have been used.
ii. Some birds have been found in controlling aquatic
weeds. For example, Swans, Ducks feed on algae like Wolffia,
Lemna, Marginal grasses etc.
Aquatic weeds have economic value. They are used for
various purposes. The removal cost of aquatic weeds by manual,
mechanical and chemical methods is high and this cost can be
compensated by utilizing the weeds for the following purposes
Native aquatic plants are an important part of the ecosystem,
but invasive aquatic weeds degrade the pond habitat and limit the
use of affected waters. Most aquatic weeds have been intentionally
introduced, so exclusion or prevention is the first line of defense
against them. Once a pond has been invaded, several strategies can
be used to manage aquatic weeds, including cultural, mechanical,
biological and chemical control. Pond owners should first identify
the invasive species, then select a product labeled for that weed
and for the situation, making sure to apply the product according
to label instructions to avoid damage to native plants and fish.