Phytoplankton ~ Greenwater:
Phytoplankton is composed mainly of microscopic free floating or suspended
algae and is generally referred to as Greenwater by aquarium hobbyists. The
green colour is the result of chlorophyll produced by algae, as freshwater
phytoplankton is usually rich in green algae. However, it also includes
diatoms, blue-green algae, and flagellates. Phytoplankton contain proteins,
starches, fatty acids and oils and is an important part of the food chain in
fresh water environments. An adequate supply of nutrients, including carbon
dioxide, enables Phytoplankton to transform the light energy of the sun into
energy-rich chemical components through photosynthesis. Phytoplankton is an
excellent primary food source for newly hatched rainbowfish larvae.
Phytoplankton also serves as food for Zooplankton, which in turn are fed
upon by the fish larvae. Some have a symbiotic existence with lower animals
such as Hydra, which has a symbiotic relationship with Chlorella algae.
The majority of Phytoplankton is made up of Holoplankton, organisms that
spend most of their life cycle in the planktonic community. However, many
phytoplankton species are capable of producing resting spores, which can to
be found in deeper water or in the bottom sediment of fresh water habitats.
These 'resting stage' spores are generally what causes the algal blooms that
we often see in freshwater environments.
Most Phytoplankton are very small, often minute organisms ranging in size
from 0.2 to 2 mm in length that drift with water currents. Like terrestrial
plants, Phytoplankton uses carbon dioxide, release oxygen, and converts
minerals to a form animals can use. In fresh water, large numbers of green
algae often colour lakes, rivers and ponds. Some blue-green algae may be
toxic or affect the taste of drinking water. Although, it is generally
believed that Blue-green algae are actually bacteria and not algae.
Cultivation of Phytoplankton for feeding rainbowfish fry is very simple. All
that is required is water, light and nutrients, and if the culture is well
managed will produce healthy juveniles. Natural sunlight is best, if not
mandatory, as without strong light the Phytoplankton will simply not grow.
Perhaps the simplest way is just to place some old aquarium water from one
of your waterchanges into a suitable container and store it outdoors. When
it turns green you can then collect a portion of the culture each day to
feed to your fishes. If on the other hand you want to culture your
Phytoplankton indoors then the best way is to use a bare 50-litre aquarium
placed near a window that receives several hours of natural sunlight each
day. Fill the tank with old aquarium water and it should turn green within a
few days. Mechanical circulation can be used to keep the algal cells in
suspension, thus exposing as much surface area as possible to the light for
photosynthesis, while making sure they don't remain in the same spot too
long for photo inhibition to become a factor. Cultures are generally
maintained at a temperature range of 20-24°C, pH 7.5-8.5. High-density
cultures may require a pH buffer to prevent pH drift.
You could even set up a bank of 50 litre aquariums as raising tanks for
rainbowfishes and simply place the spawning mops into the greenwater tanks
for hatching. The culture needs to be very thick whereby; the bottom of the
tank cannot be seen through the greenwater when looked at from above. When
the eggs hatch the fry will survive and grow without any additional help
from you. As the fry grow you can start feeding brine shrimp nauplii and
other foods until they are large enough to move to a more suitable
environment. As the fry develop you may need to add some form of filtration.
The only problem you are like to face raising rainbowfishes in Phytoplankton
tanks is that the culture can suddenly crash, dying off as suddenly as it
appeared. The Phytoplankton simply consumes all of the nutrients in the
water and then collapses. It's important to vacuum out all of the dead algae
from the bottom of the tank as soon as possible. Otherwise, this organic
material will consume substantial amounts of dissolved oxygen from the water
as it decays and in doing so can kill all the fry. Therefore, careful
observation of the tank is required at all times.
Most aquarium related cultures of this type are generally referred to as
Infusoria. The term infusoria is a collective name for many microorganisms
and can include certain algae, bacteria, protozoans, desmids, rotifers,
paramecium and a host of other small organisms. Unless you are maintaining
pure cultures in sterile conditions your culture will have both
Phytoplankton and Zooplankton in greater or lesser degree. Cultures
maintained indoors without sufficient light will probably contain more
Zooplankton than Phytoplankton but outdoors the situation is usually
reversed. Phytoplankton cultures can also be used to raise other live foods
such as Daphnia, Rotifers and Brine shrimp.
Just an added note here about green algae - many are low in HUFA's so if you
want to get really serious about using greenwater to enrich brine shrimp
beore feeding them to your fishes you should use brown algae such as
Palvlova lutheri or Isochrysis sp. You could probably get starter cultures
of these from a biological or aquaculture supplier.
Adrian.
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Adrian R. Tappin
"Home of the Rainbowfish"
http://www.ecn.net.au/~atappin/home.htm
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