Abstract
The immune-enhancing
and antibacterial properties of Black cumin, Bunium persicum
have been reported in the literatures. The present work examined the effects of black
cumin essential oil (BEO) administration on immunity and resistance of rainbow trout,
Oncorhynchus mykiss against the pathogen, Aeromonas hydrophila. To this end, fish
were fed different levels of BEO [0%, 1% (10 g/kg diet), 2% (20 g/kg diet) and 3%
(30 g/kg diet)] for 60 days. At the end of feeding trial, the growth parameters and
immunological components of mucus and serum assayed and then fish challenged
with A. hydrophila for an additional 10 days. No significant changes were observed in
growth parameters (FCR, total weight gain, total final weight) between experimental
groups after feeding period (p > 0.05). The BEO in 2% and 3% levels enhanced the
serum and mucosal levels of lysozyme and bactericidal activity (p < 0.01). The serum
immunoglobulin (Ig) levels, alternative complement activity (ACH50) and peroxidase
activity elevated in fish administered 3% BPO (p < 0.01). Total albumin in blood, total
protein in mucus and blood increased in all BPO-administered
fish (p < 0.01). The
mucosal protease and ALP activities elevated in fish fed 2% and 3% BPO (p < 0.01).
The immune-related
genes (iNOS and C3) were up-regulated
in BEO-administered
fish, with maximum expression in fish fed 3% BEO (p < 0.01). After the challenge
with A. hydrophila, the IL-1b
and TNFα expression significantly elevated in all groups
(p < 0.01), although it was less pronounced in the EBO administrated fish. The diets
containing 2% and 3% BEO significantly decreased the fish mortality following the
challenge with A. hydrophila. In addition, less hepatocyte necrosis was observed in
these treatments compared with the control group. Based on GC–Mass
analysis of the
essential oil, some components with antioxidant and antibacterial properties such as
cuminaldehyde, ρ-cymene,
limonene and γ-terpinene
were recognized. In conclusion,
the results of the present study demonstrated that dietary BEO can enhance immunity
and increase the resistance of the rainbow trout against A. hydrophila.