Question

Ichthyophthirius multifiliis is

• A. Crustacean parasite
• B. Protozoan parasite
• C. Cestode parasite
• D. Nematode parasite

Hint:

"Ich" is the most common parasite in home aquaria and hatcheries. Remember: Ich = Protozoan = Ciliates. Its marine counterpart is Cryptocaryon irritans.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the taxonomic classification of the pathogen Ichthyophthirius multifiliis, which is responsible for the well-known "White Spot Disease" or "Ich" in freshwater fishes.

Step 2: Detailed Explanation:

• Classification: Ichthyophthirius multifiliis is a Ciliated Protozoan. It belongs to the phylum Ciliophora. Protozoans are single-celled eukaryotic organisms. This specific parasite is characterized by having a horseshoe-shaped macronucleus, which is a diagnostic feature seen under a microscope.

• Life Cycle: It has a complex direct life cycle involving three stages:
- Trophont: The feeding stage found embedded under the fish's skin or gill epithelium (this causes the visible white spots).
- Tomont: The stage that leaves the fish and encysts on the pond bottom to divide.
- Theront: The free-swimming, infectious stage that must find a host within a short period to survive.

• Pathology: The white spots are actually the host's reaction (hyperplasia and mucus production) to the trophont feeding on the tissues. In severe cases, it causes respiratory distress and osmotic imbalance, leading to high mortality.

• Other Options: It is not a crustacean (like Argulus), nor is it a multicellular worm like cestodes (tapeworms) or nematodes (roundworms).

Step 3: Final Answer:
Ichthyophthirius multifiliis is a protozoan parasite.