Fish Health, Disease Diagnosis and Control
What the exam tests
Fish health questions test recognition of disease signs, diagnosis, treatment and prevention. You should link outbreaks to water quality, stocking density and pathogen introduction, and know why diagnosis comes before treatment.
Core rules
- Poor water quality, handling stress and overcrowding predispose fish to disease.
- Common signs: abnormal swimming, gasping, loss of appetite, skin lesions, ulcers, gill discolouration, white spots, cottony growth and external parasites.
- Diagnose by history, clinical examination, microscopy of skin and gills, and, where available, culture or laboratory tests.
- Epizootic ulcerative syndrome (EUS) causes deep ulcers and is linked to a fungus-like oomycete; it is not treated by antibiotics alone.
- Use salt baths, lime, potassium permanganate or formalin only at correct doses; antibiotics require veterinary advice and withdrawal periods.
- Quarantine new stock and disinfect nets and equipment.
Worked example
A 1,000 L tank needs a 3 g/L salt bath. Salt required = 1,000 x 3 = 3,000 g = 3 kg. Reasoning: dose is mass per volume; convert litres to the same unit system. A 0.1 percent bath is 1 g/L, not 1 kg/L.
Traps
Do not treat without a diagnosis. Do not use antibiotics prophylactically. Do not confuse EUS with a simple fungal infection. Do not ignore water quality after treatment.
Key facts
Argulus is a crustacean parasite. Lernaea is an anchor worm. KMnO4 is used for external disinfection.