Page 16 - FULL YEAR BOOK 2021

Editorial

Monitoring.

One aspect of RAS that is very impor-
tant is the monitoring and management
of the systems and their parameters.
Each stage must be closely monitored to
ensure optimal water parameters. As the
system is based on many sub-systems,
pumps, electrical devices etc. that tend
to fail, it is essential to have a real-time
monitoring and alarm system for oxy-
gen, water flow, ammonia, CO2, pH etc.
Backup systems including electrical and
oxygen are essential due to the limited
response time (high fish biomass will
strip the oxygen from the water within
minutes) the system has.
Aqua Feed.

3. Removing excess CO2 and oxygen- Feed for aquatic organisms are, in
ating the water through ‘de-gassing’ via many cases, made with the assumption
exchange and passing of atmospheric air that the fish and/or shrimp are growing
and water. This can be followed by fur- in an environment that can contribute
ther oxygenation of the water with pure to their nutrition. For example, ponds Taste.
oxygen. De-gassing columns are used, in develop a natural biota with time after
which a large volume of air is pushed up inoculated. This biota contributes to the In some case, It was identified that fish
by blowers and passes through the water nutrition of the culture organism. By na- reared in RAS have a muddy off-flavor.
droplets. ture, RAS is a ‘clean’ system without any The amount of off-flavor will vary with
nutritional input aside from the feed. the system, water quality parameters,
4. Disinfecting the water to remove and Moreover, especially in shrimp culture, species and size of fish, and even indi-
eliminate pathogens using UV radiation the feed needs to be stable in the water vidual variations. The source of the off-
and/or ozone. This is an essential stage for a longer period of time to prevent flavor is accumulation of the cyanobac-
that removes all or most of the bacteria increased organic load on the system. teria metabolites geosmin (GSM) and
and viruses from the water. However, feeds designed for RAS have 2-methyl-isoborneol (MIB) in the fish.
In many cases some of these processes recently started to become available Eliminating the off-flavor is slower than
are combined into one apparatus such as and, in most cases, standard feeds are uptake, and the rate of elimination is re-
a protein skimmer which removes organ- still used in RAS. duced as water temperature decreases
ics, disinfects the water (when ozone is and tissue lipid content increases. Man-
used) and enriches the water with oxy- agement of off-flavors caused by aquatic
gen. microorganisms is difficult under com-
mercial conditions. Strategies include
eliminating odor-producing cyanobac-
teria from culture systems (using ozone)
or purging the fish without feed in clean
water before harvesting. In many cases,
new RAS are designed to deal with this
issue.
Summary.
Recirculating Aquaculture Systems
technology is fast developing around the
world. It presents many advantages over
traditional culture systems such as ponds
and cages. While it seems that RAS is the
way forward for certain species and lo-
cations, it is still relatively new and may
not result in good Return On Investment.

14 Arab Agriculture 2021

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