Bacterial gill disease in fish may be caused by which of the following?

• A. Too much antibiotic in the water
• B. Water temperature maintained above 26 °C
• C. Not enough ammonia dissolved in the water
• D. Microsporidiosis

Answer: (B)

Elevated water temperature stresses fish and speeds up bacterial growth, making gill infections more likely. When the water is kept around 26 °C or higher, opportunistic bacteria that target gill tissue can multiply quickly, and the fish’s immune defenses may be less effective under heat stress. This combination creates favorable conditions for bacterial gill disease to develop, so temperature elevation is a common, driver factor.

By contrast, having too much antibiotic in the water would suppress bacteria rather than cause a bacterial infection; not enough dissolved ammonia isn’t a recognized trigger for bacterial gill disease (ammonia toxicity occurs with excess, not deficiency); and microsporidiosis is a parasitic infection, not bacterial.