Final answer:
Nitrifying bacteria convert fish waste into nitrites and then nitrates. These compounds can be utilized by plants or converted back to nitrogen gas in the denitrification process.
Step-by-step explanation:
Nitrifying bacteria play a crucial role in the nitrogen cycle by converting fish waste into forms that plants can use or that can be released back into the atmosphere. When fish excrete waste, it includes ammonium ions (NH4+). The nitrification process involves two main steps: first, the ammonium is oxidized to nitrites (NO₂⁻) by bacteria like Nitrosomonas. Following this, nitrite oxidizing bacteria further process the nitrites into nitrates (NO₃⁻), which can then be taken up by plants or later converted back into nitrogen gas through the denitrification process carried out by other types of bacteria such as Pseudomonas and Clostridium.