Fish food organisms are essential for the developmental stages of many aquatic organisms. They are very important in the critical phases of finfishes and shellfishes for their better survival and growth. They are rich in proteins, carbohydrates and essential fatty acids.

1. Collection and Isolation of Live Feed
Organisms Using Various techniques
Jadhav Amit Waghambar
M.F.Sc. I Year
AQC-MA-09-03

2.  Fish food organisms are microscopic organisms naturally
present in the aquatic environment as primary food for
the larvae of finfish and shellfish.
 Fish food organisms are essential for the developmental
stages of many aquatic organisms. They are very
important in the critical phases of finfishes and
shellfishes for their better survival and growth. They are
rich in proteins, carbohydrates and essential fatty acids.
 The availability of good quality and quantity of live foods
contribute to successful operation of aqua-hatchery
both for intensive and small scale operations.

3. Collection from the wild:-
 can be collected from seawater bodies as well as freshwater
lakes or ponds.
Collection techniques:-
1) Plankton nets :-

4.  Plankton may be collected by towing through the water
by special plankton nets made of fine silk bolting cloth
(180 meshes/inch2). A small vial is attached to the end
of the net which serves as a collector. Collected samples
may also be centrifuged or filtered. Samples for
examination may be preserved in 10–15% formalin.

5. Isolation of plankton species from collected
samples
1.Isolation of single cells:-
 Cell is picked from the sample using a micropipette or
glass capillary under microscopic observation.
 Transferred to sterile droplets of water or suitable media
 The cells can get damaged due to shear stress caused by
micropipette or capillary tips.

6. 2. Serial dilution :-
 the most common conventional and established
method of microalgae isolation from collected samples.
 stepwise dilution of a substance in sterile solution. The
dilution factor is usually constant at each step, resulting
in a geometric progression of the concentration in a
logarithmic manner
 highly dependent on the accuracy of a measured
amount of cell culture during transfer from one
medium to another. The present method is helpful for
production of algal monoculture; however these are
generally not axenic cultures.

9. 3. Streak plating:-
This method of isolation is recommended when size
of desired algal species is about 10 micrometres or less.

10. cover, incubate the plate 4–8 days under suitable conditions for
growth
place 1–2 drops of natural collection near the periphery of the agar.
Flame-sterilize a wire loop or a glass rod using 70% ethanol and
alcohol lamp. Make parallel streaks of the suspension of the agar.
prepare Petri dishes containing sterile growth medium solidified by
1–1.5% agar

11. once growth is observed, transfer desired algal units to
liquid or agar medium
Observe under high power objective of a compound
microscope
remove a sample of the desired colony using a wire loop
and place in a drop of sterile medium on a cover glass

14. 4. Density centrifugation:-
 applies gravity settling to separate organisms based on
the cell size
 Usually applied to separate larger organisms from the
microalgal cells.
 Density gradient (Example: Silica sol, Percoll) centrifugal
technique separates the different species of microalgae
into different bands.
 The delicate cells might get damaged due to shear
stress generated during centrifugation.

15. • 10-20 ml of aliquot is centrifuged in an electrical centrifuge at
1500-2000 rpm for 15 to 30 minutes.
• supernatant water is decanted until the volume reduced to 1/10
to 1/30 of initial sample.
• add few drops of 1% potassium aluminium sulphate to ensure
the precipitation of phytoplankton.
• samples are preserved using neutralized formalin or lugol’s
iodine for further examination under microscope.