2.3.3. Isolating/obtaining and maintaining of cultures
Sterile cultures of micro-algae used for aquaculture purposes may be obtained from
specialized culture collections. A list of culture collections is provided by Vonshak (1986) and
Smith et al. (1993a). Alternatively, the isolation of endemic strains could be considered
because of their ability to grow under the local environmental conditions. Isolation of algal
species is not simple because of the small cell size and the association with other epiphytic
species. Several laboratory techniques are available for isolating individual cells, such as
serial dilution culture, successive plating on agar media (See Worksheet 2.1), and separation
using capillary pipettes. Bacteria can be eliminated from the phytoplankton culture by
washing or plating in the presence of antibiotics. The sterility of the culture can be checked
with a test tube containing sea water with 1 g.l-1 bactopeptone. After sterilization, a drop of
the culture to be tested is added and any residual bacteria will turn the bactopeptone solution
turbid.