Question

Aphanomyces invadans, which causes seasonal epizootics in wild and farmed fish, is a

• A. Bacteria
• B. Virus
• C. Parasite
• D. Fungi

Hint:

EUS (Epizootic Ulcerative Syndrome) = Aphanomyces invadans = Fungus.
It is most prevalent during winter (low temperature) or after floods. It has a very broad host range, affecting over 100 species of fish.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the biological classification of Aphanomyces invadans, the pathogen responsible for EUS (Epizootic Ulcerative Syndrome).
Detailed Explanation:

• EUS Overview: Epizootic Ulcerative Syndrome (also known as "red spot disease") is a devastating disease of freshwater and estuarine fishes in Asia and Australia. It is characterized by severe deep ulcers and granulomas.

• Pathogen: The primary causative agent is {Aphanomyces invadans. This organism is an Oomycete (water mold).

• Classification: In traditional and common fisheries terminology, Oomycetes are classified as fungi (Statement D). Although modern phylogenetics places them in the group Stramenopiles (closer to algae), they are consistently referred to as fungal pathogens in standard fish disease curricula.

• Mechanism: The fungal hyphae invade the muscle tissue of the fish, causing extensive necrosis and attracting a cellular inflammatory response that leads to the typical ulcers.

Step 3: Final Answer:
Aphanomyces invadans is classified as a fungus.