Training Manual Application of Genetics and Biotechnology in ...

CHAPTER 8
PROBIOTICS IN AQUACULTURE
S. KANNAPPAN AND G. GOPIKRISHNA
Probiotics can be defined as live microbial food that improves the health of
man and terrestrial animals. In aquaculture context, it is sometimes termed as a
biocontrol agent or a bio-remediator, which means that the microbe, when added to
the water body is taken up by the fish, passes through the intestinal tract, and may
survive there. The gastrointestinal biota of fish is just a reflection of the water biota,
as a large volume of water passes through them or is filtered by them. Most of the
probiotic preparations include microbes belonging to family Vibrionaceae, the
Pseudornonads, Lactic acid bacteria, Bacillus spp and yeasts. Some of the main
characteristics expected of a successful probiotic would be its antagonistic activity
against spoilage and pathogenic organisms and the ability to colonise in the gut.
Probiotics have got the ability to afford resistance to disease causing agents.
There is also the competitive exclusion of the pathogens for nutrients or adhesion
sites and immunostimulatory activity. Though the probiotic concept has been
extended from humans, terrestrial animals to aquatic animals, there are certain basic
differences in the embryonic development that should be learnt first in order to decide
the best age for probiotic treatment. Man and terrestrial livestock undergo embryonic
development within the amnion whereas the larval forms of fish and shellfish are
exposed to the external environment at an early ontogenic stage. Hence, these larvae
get exposed at an early stage to gastrointestinal tract disorders due to microbes as they
feed even before the tract is fully developed (Timmermans, 1987) and the immune
system complete (Vadstein, 1997). Probably the best time for probiotic treatment in
aquatic system is the larval stage to get the desired effect.
In the digestive tract of fish, the bacterial flora are predominantly Gram-
negative anaerobes (Clements, 1997). In crustaceans, marine fish and bivalves, the
two common genera recorded are Yibrio and Pseudomonas (Moriarty, 1990; Prieur et