Fish Health, Disease Diagnosis and Treatment
This domain tests recognition of health problems, separation of disease from water-quality stress, and safe treatment. The exam favours prevention, diagnosis and common parasitic or fungal conditions over exotic drug lists.
Core rules
- Prevention: screen and quarantine new stock, avoid overcrowding, keep water quality stable, remove dead fish, disinfect nets and tools.
- Diagnose by history, behaviour, skin, gills and internal organs. Gasping can mean low oxygen, not infection.
- Common signs: white cottony growth (fungus), tiny white spots (protozoan), visible copepods or leeches (parasites), ulcers and fin erosion (bacterial or environmental).
- Treat only after identifying the cause. Salt baths, potassium permanganate and formalin have specific uses and risks; dose by water volume and test on a few fish.
- Never use antibiotics for viral, fungal or water-quality problems; misuse harms fish and leaves residues.
Worked example
Early morning: many fish gulp at the surface; pH is normal; dissolved oxygen is 2.5 mg/L. Reasoning: the behaviour and low oxygen point to oxygen stress, not a contagious disease. Stop feeding, start aeration or exchange water, and reduce manure. Do not add antibiotic. Recheck oxygen at dawn before deciding on further treatment.
Traps
Do not diagnose from one sign. Do not treat the whole pond before checking water volume and fish tolerance. Do not confuse saprolegniasis (cottony patches) with a bacterial ulcer. Do not apply lime and medication together without checking compatibility.