questions: asked about fish mortality and water surfacing. 
 answers: fish mortality due to lack of oxygen-immediately change water @30% or give aeration using aerators.
potassium permanganate @250gms/0.1 ha and agitate the surface with bamboo.
immediately stop application of fertilizers and feed.
use oxyzen tablet (20-24 cakes/acre), oxy more tablets (20 tablet/bigha or 200 gm/bigha).