Report 2 of 5: A Cagey Concern - Bangladesh

Introduction

Fish is an important part of the diet for the people in Bangladesh and the supply is significant in nutritional terms, providing 80% of animal protein and 8% of the total protein intake of the average diet. Fish are important sources of calcium, fats and vitamins. Fish catches vary throughout the year but are highest after the monsoon rains when supplies of other foods, such as rice, are low. Capture of small, low value fish is particularly important for the extremely poor after the rice harvest when the demand for their labour declines.

Seasonal flooding of the Ganges, Brahmaputra and Meghna rivers during the monsoon rains means that up to 40% of Bangladesh can be covered in water. With so much water, fishing plays a vital role in the economy of rural villages. At least 11% of the population are estimated to depend principally on the fisheries sector for their livelihood, while 73% of rural households engage in part time fishing (Fisheries and Aquatic Resources Sector Strategy and Programme 1995-2000, DFID Bangladesh).

CAGES project

CARE started a project at the end of 1995, supported by the Department for International Development (DFID) in the UK, named Cage Aquaculture for Great Economic Security (CAGES) with an objective to develop and promote aquaculture throughout Bangladesh. An enormous variety of water bodies, including rivers, irrigation canals, flood plains, beels (large depression), ox bow lakes and ponds are dispersed throughout Bangladesh offering considerable potential for cage aquaculture.

Site selection

The sites for the cages are selected by using set criteria:

• Available groups adjacent to water

• Access to water

• More than 1 metre water retention capacity for at least 6 months

• Little disturbance from water traffic

• Availability of seed and feed nearby

• Pollution free

• Low tidal affects and current

• Low turbidity

A cage is a very simple means of restraining fish in one place and it can be easily made using local materials. Cage design must incorporate certain physical properties, including the ability to hold fish securely but also to be within the financial means of the potential cage operators. The cages presently used by the CAGES project are small in size, measuring between 1 and 2m³, inexpensive and simple to construct.

Farmers involved in the CAGES project use both fixed and floating cages. In general, fixed cages are installed in water where the depth is relatively low and bamboo poles can be fixed into the river bed or substrate. Floating cages do not have this limitation and can also be used in deep water. Floating cages tend to be easier to manage than fixed cages but when selecting the type and design the following points should be considered:

• Ability

• Input availability

• Natural disaster

• Type of water body

• Water depth

• Water current

• Water retention period over one year

• Social problem

• Cage management

Fixed cages

Fixed cages are very easy to construct and require only a small capital investment. The materials needed to make fixed cages are netting with an 8mm mesh size, bamboo, rope, twine and sinker. Routine management is difficult for these cages and storms, strong currents, tidal surges and flooding may cause damage if precautionary measures are not taken. Fixed cages are difficult to move from one place to another during water fluctuation.

A top cover is usually provided on cages to reduce the risk of fish escaping, especially in areas prone to flash floods where water levels rise very quickly. A small opening is kept at one edge or in the middle of the top covering for feeding purposes. A feeding platform made of fine mesh is placed on the bottom of each cage to minimise food loss. To fix the cage, four bamboo poles are fixed in the substrate and the four top and bottom corners of the cage are tied to the bamboo poles with nylon rope, allowing the cage netting to stretch.

To minimise installation cost and to reduce daily management labour, cages are sometimes fixed in rows with a narrow space between the adjacent cages.

Floating cages

The size of the cage is usually 1m³ (1m x 1m x 1m). A top net is always used to minimise escapees because the cage is only a few centimetres above the water surface. The top of the cage is on hinges that can be opened to allow feeding, the checking of fish, the removal of waste and harvesting.

A layer of fine mesh net is placed along the bottom of the cage and 10 centimetres up each side which reduces food loss. However, where water has a high turbidity, the use of fine mesh is not recommended as it clogs up the mesh and causes structural stress on the cage frame. In these areas, feeding trays should be used instead of fine mesh. Buoyancy is achieved by using four plastic floats (buoys) which are tied to the four horizontal frames, approximately 10 centimetres from the top of the cage.

Bamboo frame cage

To make a 1m³ bamboo cage, twelve one metre long bamboo sticks (about 2cm in diameter) are required and fixed into the holes of the angles, one angle for each corner, giving a box shape.

Advantages and disadvantages of fixed and floating cages
 

Fixed cages	Floating cages
Advantages	Advantages
Cost per unit is small Not damaged by storms Easy cage management Cage bags spread properly in the water Easy to construct	Water volume remains constant even with a fluctuation in the water level Cage can be installed in deep water Floating cage with box type frame gives adequate space inside In tidal water bodies effective cage depth is higher
Disadvantages	Disadvantages
Water depth inside cage varies with the fluctuation of the water level Vulnerable to tidal surge and storm Cage cannot be installed in all types of water bodies Prone to crab cutting Poorer fish growth and higher mortality rate	Cost per unit is higher than fixed cages Algae deposits on cage net affect the water exchange Cage management i.e. cleaning, moving and sampling are not easy Due to water flow sometimes the cage bag does not spread properly Easy to steal fish by lifting the cage During flooding may wash away

Cage management

Care of cages – cleaning of aquatic weeds nearby, removal of water hyacinth, cleaning of waste feeds from cages, cleaning of deposited silts from cage, removal of dead fishes, checking cage frames, floats, ties, anchors, feeding trays etc., cage shifting, considering the water level, checking water pollution and guarding.

Care of net – Algae attachment should be cleaned at regular basis to ensure water exchange, net holes must be checked properly and need quick repairing when necessary.

Care of fish – profitability depends on proper attention to the fish growth, regular, adequate and quality feeding is important. Fish health and disease should be monitored during feeding and sampling. The fish must be feed daily using aquatic weed or a mixture of rice bran, oil cakes, kitchen waste, chopped snails or cow dung.

Minimising risk of cage culture

• Appropriate cage design can help minimise failure.

• The use of more than one cage per household greatly reduces the risk of an individual losing all fish.

• Placing many cages together in clusters also reduces the risk of poaching.

• Individual farmers can form groups which can guard the fish and therefore considerably reduce potential poaching threats.

Fingerling production – culture cycle is between 1 and 2 months. Cage nursery producers sell fingerlings to the pond farmers and ox-bow lake operators.

Fish for food – culture cycle is between 4 and 6 months. Fish food producers consume the cage fish as well as selling them in the market.

Profitability in cage aquaculture depends on many factors including the type of water body and culture, cage construction materials, the choice of fish species, fingerling size and price, stocking density, feed price, availability of protein rich feed, culture duration, cage management, harvesting and marketing.
 

For further information, please contact:
 

CAGES Project CARE – Bangladesh House #65 Road #7A Dhanmondi Dhaka Bangladesh Tel: +880 2 814195-8 / +880 2 814207-9 / +880 2 9118460 / +880 2 9111804 Fax: +880 2 814183 E-mail: carebang@bangla.net

Intermediate Technology Development Group would like to thank CARE-CAGES Bangladesh for providing the original material on small-scale cage aquaculture practices and cage design in Bangladesh.

This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.

TVE/ Practical Action gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.