Phosphorus uptake by Microcystis during passage through fish guts

Herbivorous fish feed on cyanobacteria. Digestability differs, however, between cyanobacteria species without mucous cover and mucilaginous genera such as Microcystis . The latter can pass fish guts almost undamaged, and it has been hypothesized that they can take up nutrients during gut passage. Here we tested whether live Microcystis , as food for juvenile roach labeled with 33 P, indeed showed higher radioactivity after gut passage as compared to gut contents in control experiments with fish fed heated Microcystis . Microcystis showed high viability after passage through roach guts, and live colonies had a significantly higher radioactivity than dead ones. We conclude that Microcystis is protected against digestion in roach guts and can directly use the phosphorus supplied in the fish guts during passage.