CONTENTS-
Abstract
Background Information
Objectives
Study Area
Results
Problems
Discussion

Flood plains of Brahmaputra basin is either eutrophic or in the process of attaining higher trophic level. A recent survey has revealed that there are 3153 wetlands covering an area of 1,01232 ha comprising 1.29% of the total geographical area of Assam. These wetlands (locally known as beels ) harbour   a wide array of   ornamental fish species and they are in fact considered as fish granary of the state, producing about 160kg/ha /yr, which   can be increased by many fold. with proper strategy and management. Over exploitation of resources mainly fish from these wetlands coupled with large amount of water withdrawal or conversion of low lying land for agricultural purposes have already threatened the wetland habitats. Indiscriminate   killing of fish by using pesticides and other illegal devices is another major threat to the already depleted fishery resources of the flood plain lakes. The present   paper deals with the status of ichthyofauna of certain wetlands of upper Assam with special reference to Dibru Saikhowa biosphere reserve.

Wetlands of Assam are considered as fish granaries   of the state producing about 16,200 (t) of fish annually. Geoclimatic condition of Assam is quite conducive for fish production. Beels are major breeding ground for many riverine fishes (IMC). Wetland comprise of 1.29% of the total geographical area of Assam. 3153 wetland covering an area 1,01,232 ha, where the average fish production is 160 Kg / ha / yr. Wetlands locally known as beels are basically of two types: Open and close beel.

Open beels get privilege of autostocking and hence there is seasonal variation in species composition whereas the closed beels have their own residential population. The dominant fish species of closed beels are air breathing fishes.

The objectives of the present study were:

Ecology and fisheries of certain upper Assam beels   were studied with special reference   to Guijan beel i.e., an open beel in Dibru-Saikhowa national park. The Dibru-Saikhowa National Park is ranked 5th and is the eastern most national park of Assam extending from 27 ° 35 ¢ to 27 ° 45 ¢ latitude and 95 ° 10 ¢ to 95 ° 40 ¢ longitude   covering an area of 340 sq. km. The area is   flood prone, which is the cause of diversity and abundance of aquatic bodies. The biotic and abiotic factors were studied   as per the standard methods of APHA, Goyal and Trivedi.

Certain limnological parameters of Guijan beel

            Maximum length (monsoon) (m) – 1500

            Minimum length (winter) (m) – 1200

            Maximum breadth (monsoon) (m) – 800

            Minimum breadth (winter) (m) – 353

            Maximum depth (monsoon) (m) – 6.5

            Minimum depth (winter) (m) - 0.8

            Area – 6.2 ha – 8 ha

            Soil Type – 35% sand 26% clay

            pH – 5.5 – 6.2

            Water Temperature - 10 ° C (Dec.) - 40 ° C (July)

            Conductivity – 79 – 104 m mhos

            DO – 4 mg / l   - 11 mg / l

            CO 2 – 1.2 – 5.5 mg / l

            Alkalinity – 30 – 85 mg / l.

•  The residential fish fauna of Guijan beel is dominated by murrel and other air breathing fishes of Channa species

•  It also harbours a wide variety of ornamental fish.

Eutrophication : Most of the beels are highly weed infested and they cover the surface of the beels. This restricts the movement of fishes and reduces dissolved oxygen in water: Gradual accumulation of aquatic weeds and siltation has   turned the beel into swamps.

Encroachment of beels : A large number of beels are encroached by the people to utilise them for   purposes other than   fishing activities. In some beels during winter, people use link channels for agricultural purposes, and as a result link channels become shallow and unproductive.

Fish Mortality: Fish disease is one of the main causes for declination of fish production in beels. Presence of excessive decayed organic matter due to dead aquatic vegetation harbours high bacterial load   causing wide fluctuation of dissolved oxygen and carbon-di-oxide   resulting in various types of fish diseases. The most dreaded disease is EUS (Epizooitic Ulcerative Syndrome), which cause high mortality in   fish.

There are many beels, which is situated near the tea garden where large number of insecticides besides fungicides and herbicides are used. Apart from their run-off to the beels with rain water, the containers of pesticides are either thrown in the beels or are washed into the beel waters. This causes extensive damage to the fish population. It has been noticed that after every spraying operation, the fish mortality in the beels rises.

The beel ecology shows its productive environment and as a result to enhance fish production following steps should be taken into account. Construction of well designed bunds and check gates to allow free movement of fishes to beels. Most of the beels are under the control of revenue department. The disposal rights of fisheries of the beel have to be transferred to the fishery department, so that its technical personnel   can undertake the development programme. Effective eradication of aquatic weeds from beels should be done as an immediate measure. The existing laws for protection of fishing grounds should be effectively enforced. Further in order to stop indiscriminate killing of fish provisions of fisheries act should be enforced effectively to protect and develop fisheries of Assam. Beel fisheries can be developed by construction of fish ponds in the periphery of beels. Beels should be leased out for longer term so that leasers can take interest to develop the beels for better production. Beels should be protected from floods by constructing embankments. Sluice gate should be provided with screens to prevent escape of fish.

Dibrugarh University,
Assam – 786 004. India.
E-mail: mrini1@rediffmail.com