Aquarium fish diseases

Black spots on fish, also known as melanosis or black ich, are usually caused by a parasitic infection or environmental stressors. The spots are typically small, black, and often appear on the fins, body, or eyes of the fish. They may also appear as a darkening of the scales. The most common cause of black spots is a parasitic infection, which can be caused by various organisms such as Ichthyophthirius multifiliis, or "ich." Environmental stressors such as poor water quality or overcrowding can also weaken a fish's immune system and make it more susceptible to infection. Treatment for black spots may involve medication or improving the water quality in the tank.