Coastal Aquaculture and Mariculture (2+1)

Unit 4 - Water and soil quality management

4.1.1.c. Turbidity

• Turbidity is a measure of light penetration in water.
• It is produced by dissolved and suspended substances such as clay particles, humic substances, plankton, coloured compounds etc.
• Excessive turbidity can be troublesome in fish ponds and flow-through systems.
• Turbidity caused by plankton is usually desirable since it enhances fish production.
• However, turbidity caused due to clay and other colloidal particles in undesirable since it can choke the gills of fish and shellfish. It can also restrict the growth of phytoplankton.
• Water turbidity in ponds is commonly measured with the Secchi disc. It is a round disk having a diameter of 30 cm. the disk is divided into quadrants, two opposite quadrants are painted white and the other two black. The disc is attached to a rope or cable marked in increments. A measurement is taken by lowering the disk into water body until it just disappears from sight. The depth at which the disk disappears is the Secchi disc visibility usually expressed in centimeters. Optimum Secchi disc visibility in extensive and semi-intensive ponds is 25 to 40 cm.

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