questions concerning zebrafish

[JENNIFER NG]

I work at the Salk Institute in the zebrafish facility. Yesterday we 
had an increase number of dead adult fish. The frequency is 
probably 4 dead fish for every 20 adults. The dead had enlarged 
bellies and very read gills.  We believe that there was an increase 
in the oxygen content of the system water. What can be done to 
get the facility back to normal without endangering more fish?  

Thanks for your cooperation.

Jennifer