Question

Saprolegniasis in fish is caused by

• A. Bacteria
• B. Fungus
• C. Virus
• D. Protozoan

Hint:

Cotton-wool disease = Saprolegniasis = Fungal infection. It is an opportunistic pathogen that attacks weakened or injured fish.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the causative agent of Saprolegniasis, a very common disease in freshwater fishes and fish eggs.
Detailed Explanation:

• Causative Agent: Saprolegniasis is caused by water molds belonging to the genus {Saprolegnia (most commonly Saprolegnia parasitica). Although traditionally classified as a fungus, modern taxonomy places these organisms in the group Oomycetes. However, in the context of fisheries science exams, they are always referred to as fungi.

• Symptoms: The disease is characterized by white or grey cotton-like growths on the skin, fins, or gills. It is often a secondary infection that occurs after the fish has been stressed or physically injured.

• Impact on Eggs: This fungus is a major threat in hatcheries, where it can quickly cover and suffocate healthy fish eggs if dead eggs are not removed promptly.

• Environment: It thrives in cool, stagnant water with high organic loads. Treatment often involves the use of salt baths or antifungal chemicals like malachite green (though many chemicals are now banned or restricted).

Step 2: Final Answer:
Saprolegniasis is a fungal disease.