• Fish can get diseases from a variety of causes.fish image by cherie from Fotolia.com
  
  Fish can contract a variety of diseases, many of which cause visible symptoms. Some diseases are easy to diagnose visually; others come from microscopic bacteria or viruses and require laboratory tests to diagnose. Fungal and parasitic diseases are often easily treated with chemical water additives.
  
  

Parasitic Diseases

• University of Florida researchers explain that fish can get parasitic diseases from microscopic organisms. Parasites live in the skin and gills of the fish and cause a variety of symptoms, such as weight loss and irritation, which may eventually lead to death. Luckily, fish owners can add chemicals such as formalin and copper sulfate to the water that kill parasites.
  
  

Fungal Diseases

• Fungal spores tend to attack weakened areas of fish, according to the University of Florida. According to the University of Georgia, fungi tend to grow on infected wounds or dead tissue on fish. Fungi usually resemble cotton, but they may also look brownish. Anti-fungal chemicals added to fish tanks help fight infections.
  
  

Viral Diseases

• It's difficult to diagnose viral diseases without laboratory tests that distinguish them from bacterial diseases, according to the University of Florida. Symptoms may include bulging eyes, bloody fins, a swollen body cavity, sores and lesions.
  
  

Bacterial Diseases

• Bacterial diseases are usually impossible to distinguish from viral diseases without laboratory tests. Bacterial skin diseases sometimes come from rough handling of the fish.
  
  

Tapeworms

• Tapeworms live in the intestines of the fish and typically cause weight loss as they steal calories from the fish's diet. Fishermen may notice tapeworms when cleaning fish.