Which statements correctly describe the roles of Nitrosomonas and Nitrobacter in nitrification?

• A. Nitrosomonas converts ammonia to nitrite
• B. Nitrobacter converts nitrite to nitrate
• C. Both A and B
• D. Neither A nor B

Answer: (C)

Nitrification happens in two linked steps carried out by different bacteria. Nitrosomonas starts the process by oxidizing ammonia to nitrite, using ammonia from fish waste as its energy source. The next step is handled by Nitrobacter, which oxidizes that nitrite to nitrate. Because each step depends on the previous one, both activities together describe the full nitrification pathway. In aquaculture, this sequential conversion is crucial: ammonia and nitrite are toxic to fish, while nitrate is far less harmful and can be managed through water changes, plant uptake, or denitrification. These bacteria thrive in well-oxygenated biofilters under appropriate pH and temperature, forming a cooperative system that maintains safer water quality. Thus, stating both roles together accurately captures how nitrification operates.