VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

QUANTITATIVE ANALYSIS OF PHYTO AND ZOOPLANKTON

Enumeration of net phytoplankton

• The plankton sample collected (through net bags or nets) and concentrated is poured into a measuring cylinder. Depending on the density of the phytoplankton, the sample is diluted and the final volume is accurately noted. The contents of the measuring cylinder are then transferred to a shaking vessel (round flask). A Stempel pipette is used to collect subsamples of desired volume (Stempel pipettes of 0.1-0.5 ml volumes are available in the market)

 

Stempel pipette

Counting of plankton in Sedgewick Rafter counting cell

• With the help of a Stempel pipette, one ml of plankton sample in transferred to a Sedgewick Rafter counting cell which is made as follows. A glass plate of suitable size or preferably a microscopic slide is taken and to its all side edges, suitable sized glass strips having 1 mm thickness are cemented using an adhesive. The cavity so formed should be of 50 x 20 x 1 mm to hold a plankton sample of 1 ml. The floor of the chamber plates is then marked out into squares of equal size using a diamond tripped pencil. The cell with the phytoplankton for counting is placed under a microscope provided with a mechanical stage. The counting is performed after an hour of sedimentation of plankton in the cell.

Sedgewick rafter

Source : http://www.2spi.com/catalog/standards/sedgewick-rafter-counting-cell.shtml

• The total number of phytoplankton present in a litre of water sample can be calculated using the following formula.

 N= (n x v) / V

• Where N - Total number of phytoplankton cells per litre of water filtered

n - Average number of phytoplankton cells in 1 ml of plankton sample taken for counting

v - Volume of plankton concentrated (ml)

V - Volume of total water filtered (l)

• In order to get the actual density of all phytoplankton present in a unit volume of water, it is necessary to include the nanophytoplankton species and their density obtained in sedimentation method with the net phytoplankton density.