Fish health is one of the most scoring — and most feared — topics in fisheries exams. Whether you are preparing for ICAR, state fisheries exams, or a university viva, the same diseases keep coming back: EUS, white spot, columnaris, Argulus, anchor worm and more. This set of 20 multiple-choice questions covers the causative agents, symptoms and prevention basics every fisheries student should know. Try them first without peeking at the answers, then check your score at the end.
20 Fish Disease MCQs
Q1. Epizootic Ulcerative Syndrome (EUS) in fish is primarily caused by
(a) Aeromonas hydrophila
(b) Aphanomyces invadans
(c) Saprolegnia parasitica
(d) Flavobacterium columnare
Q2. White spot disease (Ich) in freshwater fish is caused by
(a) Ichthyophthirius multifiliis
(b) Cryptocaryon irritans
(c) Trichodina sp.
(d) Gyrodactylus sp.
Q3. Columnaris disease, also called cotton-wool disease or mouth fungus, is caused by
(a) A fungus
(b) A virus
(c) The bacterium Flavobacterium columnare
(d) A crustacean parasite
Q4. Argulus, commonly called the fish louse, belongs to which group?
(a) Protozoa
(b) Crustacea
(c) Monogenean flatworms
(d) Leeches
Q5. The anchor worm of fish is
(a) Argulus sp.
(b) Lernaea sp.
(c) Dactylogyrus sp.
(d) Piscicola sp.
Q6. Cotton-wool disease (saprolegniasis) of fish and fish eggs is caused by
(a) Saprolegnia parasitica
(b) Branchiomyces sanguinis
(c) Aphanomyces invadans
(d) Aeromonas hydrophila
Q7. The classic external sign of dropsy in fish is
(a) White spots on the fins
(b) Raised, pinecone-like scales with a swollen abdomen
(c) Cotton-like growth on the mouth
(d) Thread-like worms hanging from the body
Q8. Haemorrhagic septicaemia with red sores on the body of freshwater fish is most commonly associated with
(a) Aeromonas hydrophila
(b) Ichthyophthirius multifiliis
(c) Saprolegnia parasitica
(d) Argulus sp.
Q9. Koi Herpesvirus (KHV) disease of common carp and koi is a
(a) Bacterial disease
(b) Fungal disease
(c) Viral disease
(d) Nutritional disorder
Q10. Gill rot disease (branchiomycosis) in fish is caused by
(a) Branchiomyces sanguinis and Branchiomyces demigrans
(b) Flavobacterium columnare
(c) Trichodina sp.
(d) Lernaea cyprinacea
Q11. Velvet disease of fish, which gives a dusty, gold-coloured coating on the skin, is caused by
(a) Oodinium
(b) Ichthyophthirius multifiliis
(c) Saprolegnia parasitica
(d) Gyrodactylus sp.
Q12. Which of the following correctly pairs the parasite with its site?
(a) Dactylogyrus — skin flukes; Gyrodactylus — gill flukes
(b) Dactylogyrus — gill flukes; Gyrodactylus — skin flukes
(c) Argulus — gill flukes; Lernaea — skin flukes
(d) Trichodina — anchor worm; Argulus — gill fluke
Q13. The first sign of EUS on an affected fish is usually
(a) White cotton-like patches
(b) Small red spots on the skin that deepen into ulcers
(c) Thread-like worms on the fins
(d) Swollen, pinecone-like scales
Q14. The white spots seen in Ich are actually
(a) Fungal spores on the skin surface
(b) Feeding stages (trophonts) of the parasite embedded in the skin and fins
(c) Fish eggs attached to the skin
(d) Salt crystals from hard water
Q15. Fin rot in fish is best described as
(a) A purely viral disease of the tail
(b) Frayed, torn or eroding fins, usually linked to poor water quality, stress or bacterial infection
(c) A parasitic disease caused by anchor worm
(d) A nutritional deficiency of vitamin C only
Q16. Columnaris is also known as saddleback disease because
(a) It affects only saddle-shaped fish
(b) It can produce a saddle-shaped lesion behind the dorsal fin
(c) It is carried by horse saddles
(d) It only occurs in saddleback ponds
Q17. Trichodina is a
(a) Crustacean parasite
(b) Protozoan ectoparasite found on skin and gills
(c) Bacterial pathogen
(d) Fungal pathogen
Q18. Which is the single most important preventive step before adding new fish to a pond or tank?
(a) Feeding antibiotics for a week
(b) Quarantining the new fish and checking them for disease
(c) Raising the water temperature sharply
(d) Removing all aquatic plants
Q19. Why do the ulcers of EUS often become worse even after the fungus is established?
(a) Secondary bacterial infections commonly invade the ulcerated tissue
(b) The fish stops eating permanently
(c) The ulcers turn into tumours
(d) The fungus produces eggs on the skin
Q20. The most reliable general defence against most fish disease outbreaks is
(a) One strong chemical treatment per year
(b) Good water quality, avoiding overcrowding, and prompt removal of sick fish
(c) Keeping fish in complete darkness
(d) Feeding only live food
Answer Key with Explanations
1 — (b) Aphanomyces invadans is the primary causative agent of EUS; infection starts as red spots that become deep ulcers.
2 — (a) Ichthyophthirius multifiliis, a parasitic ciliate, causes white spot disease in freshwater fish. (Cryptocaryon irritans causes the marine form.)
3 — (c) Columnaris looks fungal but is bacterial — Flavobacterium columnare. Antifungal treatment alone will not control it.
4 — (b) Argulus is a disc-shaped, blood-feeding crustacean, easily seen with the naked eye on skin and fins.
5 — (b) Lernaea, the anchor worm, is a copepod; the female penetrates the skin and anchors in the muscle, with a thread-like body and paired egg sacs trailing behind.
6 — (a) Saprolegnia parasitica causes cotton-wool-like grey-white growths on skin, gills and eggs, especially on stressed or injured fish.
7 — (b) Dropsy shows as a swollen abdomen with scales standing out like a pinecone, reflecting internal bacterial infection affecting organs such as the kidney.
8 — (a) Aeromonas hydrophila causes haemorrhagic septicaemia — red sores, swollen abdomen and loss of appetite.
9 — (c) KHV is a viral disease of koi and common carp, marked by gasping, skin lesions, gill damage and sudden mass deaths; prevention rests on biosecurity and quarantine.
10 — (a) Branchiomyces sanguinis and Branchiomyces demigrans cause gill rot, with necrosis of the gills, favoured by crowding and high organic load.
11 — (a) Oodinium causes velvet disease — a fine, dusty, gold-coloured coating on the body.
12 — (b) Dactylogyrus are gill flukes; Gyrodactylus are skin flukes. This is a favourite examiner’s trap — do not swap them.
13 — (b) EUS begins as small red spots that spread and deepen into ulcers, sometimes reaching muscle.
14 — (b) The white spots are trophonts feeding inside the skin and fins, surrounded by host cells — not the parasite sitting on the surface.
15 — (b) Fin rot is a syndrome: frayed fins driven by poor water quality, injury, stress and secondary bacteria — fixing water quality comes first.
16 — (b) Columnaris can form a saddle-shaped lesion behind the dorsal fin, hence “saddleback disease”.
17 — (b) Trichodina is a ciliate protozoan ectoparasite of skin and gills.
18 — (b) Quarantine of new stock is the standard first line of defence; it stops new pathogens entering an established pond or tank.
19 — (a) Secondary bacterial infections are very common in EUS ulcers and worsen the damage.
20 — (b) No single chemical replaces husbandry: clean water, sensible stocking density, good feed and quick isolation of sick fish prevent most outbreaks.
Quick Revision Table
| Disease | Causative agent | Type |
|---|---|---|
| EUS | Aphanomyces invadans | Fungal (oomycete) |
| White spot (Ich) | Ichthyophthirius multifiliis | Protozoan |
| Columnaris | Flavobacterium columnare | Bacterial |
| Cotton-wool disease | Saprolegnia parasitica | Fungal |
| Gill rot | Branchiomyces spp. | Fungal |
| Fish louse | Argulus spp. | Crustacean |
| Anchor worm | Lernaea spp. | Crustacean (copepod) |
| Haemorrhagic septicaemia | Aeromonas hydrophila | Bacterial |
| KHV disease | Koi herpesvirus | Viral |
| Velvet disease | Oodinium | Protozoan |
How to Score Yourself
18–20: Exam-ready — you know your pathogens cold.
14–17: Strong — revise the fluke pair (Q12) and the fungal trio (EUS, saprolegniasis, gill rot).
Below 14: Re-read the table above, then retake the quiz tomorrow. Most fisheries exams test exactly these ten diseases.
Note: This is an educational quiz for exam preparation. Disease diagnosis and any treatment on a real farm should be done with guidance from a fisheries expert or veterinarian; no drug dosages are recommended here. The images in this post are illustrations.