Answer: yes, many different kinds
Explanation: bacteria are everywhere and so will be found in aquaria. Aquarium health is dependent on bacteria. Fish excrete ammonia which is toxic. Bacteria such as Nitrosomonas and Nitrococcus convert ammonia to nitrite, and Nitrobacter converts nitrite to nitrate which is relatively harmless. Bacteria such as Pseudomonas stutzeri and Bacillus subtilis remove nitrate and organic waste. There are also bacteria in fish intestines, and other bacteria that can cause fish diseases or create undesirable conditions such as Pseudomonas fluorescens, Vibrio, Flexibacter or Aeromonas and anaerobes that reduce sulphates to hydrogen sulphide.
