There are several potential causes for fish skin diseases which include bacteria, fungi, parasites and environmental factors. Some of the most common causes are:

Bacterial Infections - Various bacteria like Aeromonas, Pseudomonas and Streptococcus are known to infect fish skin and scales causing diseases. Improper water quality and poor hygiene increases the risk of bacterial infections.

Fungal Infections - Fungi like Saprolegnia and Ichthyophonus are often responsible for fungal skin infections in fish. Overcrowded and unhygienic conditions favor the spread of fungal diseases.

Parasitic Infestations - External parasites like Ichthyophthirius multifiliis (ich), Trichodina and Costia infect fish skin and gills. These parasites thrive in poor water quality and temperature fluctuations.

Poor Water Quality - High levels of ammonia, nitrites and low dissolved oxygen damages fish skin making them prone to secondary infections. High organic load and low pH/hardness also weakens the protective skin barrier.

Physical Injuries - Abrasions from sharp decorations, tank mates or equipment injure Fish Skin Disease allowing entry of pathogens. Improper net handling during water changes can also cause skin wounds.

Genetic Predisposition - Some fish breeds have genetic weaknesses making their skin more susceptible to certain diseases under suboptimal conditions.

Symptoms of Fish Disease

The common visible symptoms exhibited by fish with skin diseases include:

- Gray/white patches, cotton-like growths or ulcerations on the skin

- Presence of spots, dots or grains embedded in skin or patches of hemorrhaging

- Reddening, inflammation and swelling of infected areas of skin and fins

- Excessive mucus coating, erosion or scaling of the skin and fins

- Bleeding, discoloration, irritation along the bases of fins and at the skin-fin junction

- Popped out scales appearing pinhead sized or large ragged areas devoid of scales

- Bulging eyes, excessive rubbing, scratching or flashing against objects in the tank

- Lethargy, loss of appetite, erratic swimming, rapid/difficulty breathing or death.

Types of Common Fish Diseases

Some common skin diseases affecting both freshwater and saltwater fish include:

- Ich - Whitish spots caused by Ichthyophthirius multifiliis protozoan parasites.

- Fin Rot - Progressive bacterial/fungal infection around fins and base.

- Lymphocystis - Viral disease forming white cauliflower-like lumps on skin and fins.

- Columnaris - 'Cottonwool' grayish fungal growths caused by Flexibacter columnaris.

- Costia - Small white patches due to Trichodinella infection often found around gills.

- Fungus - Fluffy white/grey fungal growths on skin, often starting on the head region.

- Velvet - Gold/brown spots from Oodinium infection barely visible to naked eyes.

- Anchor Worms - Thread-like parasites embedding in skin causing ulceration.

- Bacterial Dermatitis - Pus/ulcer filled spots from bacterial pathogens aggravated by injuries.

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