Question: asking about death of fish due to oxygen deplition
Answer: apply lime @ 8 kg per bigha
after 7 days apply cowdung 130 kg per bigha per month

for oxygen apply oxymore tablet @ 20 tablet per bigha

after 7 days of cowdung dung application:  apply urea @ 3.7 kg per bigha and ssp @ 2.7 kg per bigha