What condition can cause ammonia toxicity in fish?

Low pH in the water is a critical factor that can lead to ammonia toxicity in fish. Ammonia exists in two forms in aquatic environments: ionic ammonium (NH4+) and non-ionized ammonia (NH3). The proportion of these forms is influenced significantly by the pH of the water. Specifically, at lower pH levels, the concentration of ammonium increases while the concentration of non-ionized ammonia decreases.

Non-ionized ammonia is the more toxic form that can diffuse freely across cell membranes, causing harm to fish. When the pH is low, the balance shifts towards the less toxic form, but this can still lead to elevated total ammonia levels in the water. If the buffering capacity of the water is poor (which is often the case when pH is not properly managed), small increases in total ammonia can quickly result in dangerous levels of non-ionized ammonia, leading to toxicity.

The other conditions, such as high levels of salinity, high water temperature, and inadequate lighting, do not have the same direct relationship with ammonia toxicity as pH does. For example, while high temperatures can increase metabolic rates and potentially increase ammonia production in fish through excretion, they do not directly change the chemical composition of ammonia in