The potential of duckweed
as an alternative feed
source in tilapia production
U
Henk Stander
Aquaculture Division, Department of Animal Sciences,
Stellenbosch University
sing fish feeds in aquaculture
(sometimes referred to as artificial
or aqua feeds) generally increases
productivity. Feeds usually constitute
the most important operating cost for
any farm and efficient growth and food
conversion are the main keys for profitability.
However, to maximize cost-effectiveness, it is
particularly useful in small-scale aquaculture
to utilize locally available materials, either
as ingredients (raw materials) in compound
artificial feeds or as sole feedstuffs. There is
also a vital need to seek effective ingredients
that can either partially or totally replace
marine ingredients (fish meal) as protein
sources in animal feedstuffs generally, and
in particularly in aquaculture feeds. What
potential do duckweed have as an alternative
feed option for the tilapia farmer?
Food and Feeding Habits of Tilapia:
The tilapia group exhibit a great variety of
feeding habits and though this diversity, these
fish have adapted to fill a number of different
feeding niches. This extremely successful
exploitation of the environment has enabled
them to live together and to feed at different,
non-competitive trophic levels ranging from
AgriKultuur |AgriCulture
species feeding on detritus to the swiftly
moving carnivorous forms preying on other
living organisms like mosquito larvae.
Planktonic algae would appear to be the
preferred food of Oreochromis mossambicus
and Oreochromis niloticus and are removed
from the water by extracting the algae from
the respiratory water brought in through the
mouth to oxygenate the gills. The algal cells,
whether single cells, filamentous chains or
aggregate clumps, are entangled by copious
secretions of mucus produced by cells lining
the buccal cavity. This agglutinates the small,
numerous cells, which are then raked back
into the alimentary canal by the action of the
pharyngeal teeth. This mechanism may be
supplemented by a second mechanism which
collects small particles that may have escaped
the initial mucus entanglement. A series of
fine protrusions, the micro-gill rakers, situated
on the gill arches may act as a sieve. The gill
rakers proper are probably too widely spaced
to trap any algae but only the very large
particles and therefore serve only to prevent
damage to the delicate gill lamellae by debris
and sand taken in with the respiratory water.
The more closely spaced micro-gill rakers may
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