Question: asking about death of small fish showing red eye after harvest
Answer: suggestion 
cause is due to stress as a result of harvesting 
apply potassium parmanganate @ 13 gram for 1 bigha mix with suitable amount of water and broadcast on whole pond surfacer 
followed by agri lime @ 8 kg per bigha mix with suitable amount of water and keep for 1 night and apply on the next sunny day 
wait for 1 to 2 weeks
if good result does not happened then apply oxyteracycile @ 100 mg per 1 kg feed for 5 days