Luminous Vibriosis, a bacterial disease caused by Vibrio harveyi,
is one of the major causes of the failure in crustacean larval
rearing not only in the Philippines but also in other parts of
the world. In the past, various methods have been adopted to eliminate
this harmful bacterium in the hatchery production of crustaceans such
as water treatments using filtration and UV radiation; and the use of
antibiotics. However these methods do not cause permanent changes in
the bacterial concentrations and may even lead to the development of
resistant-strain bacteria. The latest innovative method is the use
of biocontrol agents like microalgae in hatchery operations and in
grow-out ponds. Biocontrol is the use of non-virulent/beneficial
organisms such as microalgae to repress and effectively control the
growth of pathogenic bacteria.
This high impact project funded by DA/BAR/AFMA started
in 1999 with a general objective of developing a cheap and
efficient system of controlling diseases in mud crab, Scylla
serrata hatchery system using microalgae as biocontrol agent.
Preliminary results of this study showed that Vibrio harveyi
was pathogenic to zoeal stages of mudcrab Scylla serrata at 102 - 103
colony forming unit per ml. Microalgae Chaetoceros and Skeletonema
were found to have a definite inhibitory effect against Vibrio harveyi
in in-vitro co-culture experiments at a density of 105 cells per ml.
Crude methanolic extract of Nannochloropsis was proven effective in
controlling the growth of gram-positive and gram-negative bacteria as
shown by the presence of zones of inhibition in the bacterial plate
cultures. Microalgae, Nannochloropsis and Chaetoceros, contain
bioactive substances with antibacterial properties that can be
developed for disease control in crab hatchery.
Now on its third and final year of implementation (2002),
the project is evaluating effective density, delivery systems
and protocols using different live and dried microalgae for maximum
beneficial effect for the control of Vibrio harveyi in crab hatchery
system. The project is also characterizing the bioactive compounds
in the microalgae extracts responsible for vibriostatic activity.
Biotechnology manual and scientific publication will be done based
on research outputs.
The project personnels are: Dr. Jesse D. Ronquillo
(December 1999 - June 2001) and Dr. Lourdes A. Dureza
(July 2001 - present) as project leaders, Dr. Ebonia B. Seraspe
and Nieves A. Toledo as study leaders, Vonie Suarnaba as
research associate and Shiela May Baylosis as research staff.