Question

Whirling disease in fish is caused by

• A. Mixosporidians
• B. Saprolegnia
• C. Mixosoma cerebralis
• D. Ciliates

Hint:

Fish Parasitic Diseases:
Whirling Disease (Trout) $\rightarrow \textit{Myxobolus (Myxosoma) cerebralis}$ (Myxozoan).
Ich White Spot Disease $\rightarrow \textit{Ichthyophthirius multifiliis}$ (Ciliate).
Cotton Wool Disease $\rightarrow \textit{Saprolegnia}$ (Oomycete fungus).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Myxozoan fish parasitology: Myxobolus cerebralis (historically Myxosoma cerebralis) invades cartilage in juvenile salmonids, causing skeletal deformities, black tail, and erratic whirling swimming behavior.

Step 2: Detailed Explanation:
Whirling Disease of Salmonids:
- A devastating parasitic disease affecting juvenile salmon, trout (especially rainbow trout, Oncorhynchus mykiss), and char.
- Caused by the myxozoan cnidarian parasite {Myxobolus cerebralis (historically classified as {Myxosoma cerebralis).
- Life cycle alternates between the salmonid fish host and the aquatic oligochaete tubificid worm (Tubifex tubifex, producing infectious triactinomyxon spores).
- Trophozoites attack and digest the axial and cranial cartilage surrounding the inner ear and spinal cord, causing tail darkening ('black tail'), skeletal spinal deformities (scoliosis/lordosis), and loss of equilibrium leading to erratic tail-chasing 'whirling' swimming movements.

Step 3: Final Answer:
Therefore, Whirling disease is caused by Mixosoma cerebralis, matching option (C).