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Ecology And Water Quality Parameters Of Beel Fisheries In Assam

Dipanjan Kashyap1, Sonmoina Bhuyan1, Rajita Devi2, K. Kalita3 and P. K. Goswami3

1Central Institute of Fisheries Education, Versova, Mumbai-400061, India

2College of Fisheries, Central Agricultural University, Lembucherra, Tripura, India

3College of Fisheries, Assam Agricultural University, Raha, Assam, India

Email of corresponding author:


Beels constitute vitally important fishery resource of Assam. Beels are wetlands which, if judiciously managed, can furnish unimaginably high and rich benefits to the people of the state. The beel fisheries area in the state covers one lakh hectare against 2.30 lakh hectares being 43% of the country. In Assam two major river systems namely the Brahmaputra and the Barak are there and the beels are situated along the tributaries of these two river systems. In Brahmaputra valley, there exist a total of 1,030 number of beels covering an area of 92,693 hectares; out of which 306 beels (31,214 ha) are located in central Assam, 409 beels (29,383 ha) are in lower Assam and 315 beels (32,016 ha) are in Upper Assam. On the other hand, there are about 167 beels with an area of 8,122 ha in Barak valley. The potential of these beel fisheries could not be harnessed so far, as no substantial development effort could be taken up due to financial constraints. Presently these beels are under threat from many factors like pollution, reclamation, habitat degradation etc. These threats cause loss of important biodiversity of indigenous and migratory flora and fauna.

Ecology of the beels

Beel is a highly productive ecosystem which can effectively convert the solar energy into organic carbon in the presence of rich nutrients available from natural sources. Thus, growing fish in the beels is an effective way through which the gap between demand and supply of fish can be reduced. However, the ecosystem processes in open bodies are usually very complex due to the interaction of an array of physical, chemical and biological processes. Because of the combined effect of these processes on the biotic communities living in these water bodies, it is often difficult to link their fish production potential with any particular ecological parameters. The beel ecosystem is extraordinarily complex with wide temporal and spatial variations of many key parameters. Some of the important factors that influence the wetland ecosystem are depth, nature of catchment area or river basin, precipitation and duration of connection to river etc. Ecosystem processes in a beel is determined by a number of factors which can be included under three broad heads.

  1. Morphometry and hydrodynamics

  2. Physico-chemical properties and

  3. Biological characteristics

1. Morphometry and hydrodynamics

The main morphometric features that influence the productivity of beel ecosystem are shoreline area, depth and slope. These features are closely linked with the hydrodynamics of wetlands. There are three main sources of water input into the beel ecosystem viz. overspill from the river channel, surface flow and regeneration. During the period April-June heavy rainfall takes place in Assam, due to which all the beels and low lying areas are flooded with rain water. Surface run-off and increase in river height due to inflow of rain water from the upper stretches cause inundation of the floodplains, often causing resumption of connection between beels and main rivers. Therefore through the connecting channels the open beels receive the water from their parent rivers throughout the year. Permanently closed beels receive water through rainfall and surface run-off. Thus, flood is the main source of water for the beels of Assam.

After recession of flood, connecting channels are dried up due to the reduction in water level in the rivers. The water depth of the beels reduces through evapo-transpiration and seepage. In some places, people practice rabi crop and vegetable cultivation on the banks by extracting water from the beels. The water loss by various means causes shrinkage and lowering of depth in the beels. Consequently, the fluviatile nature of the system is transformed into a lentic and stagnant water body till next flooding. This seasonal change from a lotic to lentic condition and vice versa bestows the beels its unique character.

2. Physico-chemical properties

Water flow plays a vital role in nutrient dynamics and aquatic productivity through transport of nutrients to the organisms and removal of waste. Similarly, temperature, which affects all life processes including growth rate, lifecycle and overall productivity of the entire system, is a key physical variable. The flood water and surface run-off carry huge load of silt and organic matter which render water turbid, preventing light penetration. After the monsoon, the silt settles at the bottom making the water more transparent to facilitate light penetration. This increases effective photosynthetic zone making the system more productive.

There are three basic mechanisms that control the water chemistry of the beels: precipitation, evaporation and nature of the river basin. The ionic composition of water is chiefly determined by the rain and the substrata over which the parent river flows. Secondary influences on the ionic composition are exerted by macrophytes and phytoplankton. In recent years, human factors related industrial, agricultural and urban activities started playing an increasingly important role in determining the chemical quality of water. The chemical and physical load brought in by rain water or surface run-off gets concentrated by evaporation and altered by chemical and biological interaction within the system, causing seasonal variations of various parameters.

3. Biological characteristics

The living part of the ecosystem or the biotic communities in water is governed by the variations of physical and chemical features of the water body and trophic interactions associated with it. Biotic communities of the ecosystem can be catagorized broadly as autotrophs and heterotrophs. The autotrophs include photosynthetic pigment bearing microscopic plants, plankton and macrophytes; whereas heterotrophs include consumers and decomposers. Beels are generally considered as highly eutrophicated system with high rate of primary productivity. The energy produced at the primary stage i.e. phytoplankton and macrophytes are transformed into higher trophic levels through food chains. In beels, two main pathways viz. the grazing chain and the detritus chain are found. In the absence of fish feeding on macrophytes, the plants die and settle at thebottom which is later consumed by the detritivorous fishes.

Figure: A beel infested with water-hyacinth (Eichhornea spp.)

Water quality of the beels in Assam

Soil is vital in maintaining the productivity of any water body and water quality is vital for metabolic process of plants and animals living within the water body. The soil and water conditions of the beels in Assam are mentioned below.



Soil quality:


5.10 - 5.80

Organic carbon (%)

2.80 - 5.90

Water quality:

Temperature (0C)

18.50 - 31.50

Transparency (cm)

48.00 - 121.00

Dissolved oxygen (ppm)

4.27 - 11.20


6.40 - 7.60

Free carbon-di-oxide (ppm)

2.00 - 12.00

Total hardness (ppm)

13.90 - 35.60

Source: Social, economic and policy respects of Fisheries

Fish yield and fish yield potential of the beels

Beels of upper Assam has the highest average yield potential (1245 kg/ha/yr) followed by the lower (1221 kg/ha/yr) and central Assam (1060 kg/ha/yr). Barak valley beels with yield potential of 1093 kg/ha/yr was poor compared to upper and lower Assam areas of Brahmaputra valley.

Estimation of fish yield from beels of Assam is very difficult task due to the unorganized marketing activities and dissipation of catch. CIFRI have made some assessment of the fish yield on the basis of enquiries from the beel sites. According to CIFRI, fish yield are in the range of 14-488 kg/ha/yr with an average of 173 kg/ha/yr.

Management and control of beels

In Assam, normally, the beels or low lying wetlands are under the control of Revenue Department. Since 1977, about 182 beels have been handed over to the Assam Fisheries Development Corporation (AFDC) for maintenance and development of fisheries. As such under the present system, both the Revenue Department and AFDC lease out the beels for a period ranging from 5 to 7 years at a time. The prime objective of leasing beels is to earn revenue for the state’s exchequer. The protection of the interest of traditional fishermen is not given much attention under the existing policy. The system allows rich middlemen to obtain the lease. The leasees hire fishermen to do the netting and fishing. In most cases, fishermen of adjacent villages are hired at very low wages or on a shared-harvest basis mostly in the ratio of 70:30 or 60:40 between the lease and the fish catcher. The marketing of the fishes is totally controlled by the leasees. The fishermen are not allowed to sell their share of fish in the market. They have to sell their share of fishes to the leasee at a low price fixed by them.

As the lease period is short and fixed, the leasees maximize income by catching the entire stock of fish from the beel. To achieve this, the water level is often reduced by pumping it out. The fishermen also helped the leasee to maximize the catch, especially those fishermen who work on the share-harvest system. The provisions of the Fisheries Act, 1897 enacted for the protection and conservation of fish-biota are meaningless under existing management system.


Beels of Assam are rich in fish diversity and it harbours almost all freshwater species available in the North Eastern region. Due to improper fishing, lack of proper planning and proper conservation measures fish species are depleting very rapidly in the state. If it continues for another few years most of these indigenous fishes will extinct. So, immediate attention from government agencies, NGOs, researchers, planners and policy makers, local people etc. is required in this regard.


Acharjee, B., 1997. Ecological Status and Productivity Potential of Some Beels in lower Brahmaputra Basin, Assam. Unpublished Ph.D. Thesis, Gauhati University, Assam. p. 206.

Anon. Study on various species of fishes and strategy for development of Fishery sector in N.E. region: A report by AFDC.

Deka, T. K., 1999. Present Status of Beel Fisheries and its Impact on Socio-economic Condition of Fishermen Community of Assam. Unpublished Thesis, Gauhati University, Assam. p. 122.

Seafood — Fish — Crustacea

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