. The
loss of common carp industry in Israel was estimated as $1.2 million
during 1998 [7]; mass mortality of cultured common carp was
recorded during the spring of 1998, when the temperature ranged
from 22 C to 26 C. The outbreaks are often characterized by very
high mortalities at water temperatures above 16 C [8]. The bacterium,
Aeromonas hydrophila is associated with various disease
problems in carp aquaculture production worldwide [9]. The
pathogenicity of the bacteria appears to mainly affect stressed or
compromised fish, and the infection is often secondary [10].
The traditional chemotherapy yields partial success; besides
with the increasing demand for eco-friendly carp production and
restrictions imposed against the use of various chemicals and antibiotics
[11e14]. In this regard, the use of herbals and probiotics as
immunostimulants in aquaculture is gaining importance [15e18].
Furthermore, it has been proved that chemicals and antibiotics alert
microflora of the digestive tract and lead to the emergence of
resistant strains of pathogens [19]. *