Growth and potential photosynthetic activity of cyanobacteria (predominantly Microcystis spp.) passed through intestine of crucian carp and koi carp were compared with those of phytoplankton taken directly from lake during a 9 day cultivation of fish faeces in algal BG-11 medium. The cyanobacteria exhibited a significant reduction of activity in both maximum optical quantum yield (Fv/Fm) (P<0.001) and non-photochemical quenching value (NPQ) (P<0.001) after passage through the experimental cyprinid fishes. The difference in the photosynthetic activity of the cyanobacteria from crucian carp and koi carp faeces was not significant (P>0.05) for all the measurement intervals. The results provide experimental evidence that Microcystis can be damaged by crucian carp and koi carp digestion. That may be a complementary method using bio-manipulation to control cyanobacterial blooms.
Key words: Microcystis colonies, photosynthetic activity, crucian carp, koi carp, gut passage.
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