Aquaculture Engineering (2+1)

Site selection for Brackish water fish farms - Type of soil and its quality

Unit 8 - Brackish and marine water fish farms

Site selection for Brackish water fish farms

Type of soil and its quality

The type of soil and its composition at a site is of crucial importance. It has direct bearing on the productivity of pond. The site should contain soft bottom soil or mixed soil comprising of clay, sand and silt to ensure good water bearing capacity as well as production of natural food organisms on which fish and prawn could feed and grow. One of the most important characteristics is the ability of soil to hold the water. Good soil should contain a layer of impervious material thick enough to prevent excessive seepage. Clays and silty clays are excellent impervious materials. A soil permeability of K (Coefficient of permeability) less than 5 x 10-6 m/sec is desirable.

A sandy clayey soil to clayey loam soil is the best soil type for fish/shrimp pond construction. Clayey loam is an ideal soil as it has low permeability and also rich in organic matter. In case of mixed soils, clay content up to 30% is desirable. Loamy soils have great fertility. Clayey loam has both properties i.e. low permeability and high fertility. Organic matter of clayey loam helps in the production of benthic blue algae, which in turn along with some associated micro-organisms form natural food for fishes and prawns. Clayey loam soil also has high load bearing capacity, therefore it is the best material for constructing the embankments.

Soil texture requirements vary with the level of culture technology to be applied. In extensive culture system, which relies mainly on benthic organisms as natural food for the shrimp, loamy to sandy bottom is preferred. On other hand sandy clay loam to sandy loam is preferred for semi-intensive and intensive cultures where artificial food is given as main source of food. Pond bottom soil reacts with water and influences water quality. It plays a very important role in the storage and release of nutrients to water and mineralization of organic waste matter. Hence soil characteristics (Like texture, composition and fertility) govern water quality and pond productivity.