Plant protein sources have been identified to have the greatest potential to replace fish meal protein in aquafeeds.
However, plant ingredients contain significant quantities of carbohydrates, and the ability of fish to utilize dietary
carbohydrates as energy sources for growth is limited. Included in the carbohydrate group, cellulose is not tolerated
by most fish. In the present study, the grass carp, a typical herbivorous fish, fed with duckweed was selected
to study the effect of exogenous cellulase on the growth. The results of 2-month feeding experiment showed that
the cellulase promoted the growth of grass carp. In addition, the cellulase increased various digestive enzyme activities,
such as cellulase, amylase and protease but not the lipase activity. Meanwhile, the polymerase chain reaction
denaturing gradient gel electrophoresis (PCR-DGGE) analysis indicated that the intestinal microbiota of
fish fed with the supplemental cellulase changed in bacteria species and density. Band patterns derived from control
and cellulase samples showed a low degree of similarity when analyzed by cluster analysis. Some bands were
unique to control samples, whereas other bands were obtained only with samples of the cellulase group. The 16S
rRNA gene sequencing identified that Proteobacteria and Firmicutes were the two dominant groups, and the
emergence of certain bacterial strains including Bacilli and Sphingomonas may contribute to the digestion of cellulose.
The former researches and this paper results suggest that the endogenous cellulase is far from sufficient to
fully digest the ingested fiber, so cellulase should be developed as a kind of aquatic additive