2.3. Experimental design
In vaccination experiments, healthy grass carp were distributed
randomly into control group and bath immunization group (150 fish
per group). For bath immunization, fishwere immersed in 20mgL1
SWCNTs-Aera and the control groupwas immersed in PBS for 6 h. At
the end of the vaccination, grass carp were transferred to different
tanks without SWCNTs-Aera for 28 d. After 28 d, 15 fish in each
replicatewere euthanized in the laboratory throughwashrag soaked
with 20.0 g/m3 MS-222. Sampled fish were dissected immediately
with sterile scissors. The intestine, kidney and spleen were aseptically
removed from their abdominal cavity, separately, where five
fish were sampled for analyzing expression of seven immunerelated
genes through quantitative real-time PCR (qRT-PCR) and
the experiment was performed in triplicate replicates. Thereafter,
the intestine of three fish (15 fish per replicate) were also collected
and pooled together as described elsewhere to extract microbial
DNA for deep sequencing [29]. After 2 d, the remaining fish (15 grass
carp in each replicate) were intramuscularly injected with
6.5 104 cfu mL1 A. hydrophila, kept for 10 days and thereafter
euthanized for sampling. Subsequently, the intestine was carefully
excised and maintained as above, which was also for extracting
microbialDNAfor deep sequencing. All the samples were placed into
sterile polypropylene centrifuge tubes and stored in 80 C until
DNA extraction. All experiments were performed in triplicate.