National Practising Veterinarian Qualification Examination (全国执业兽医资格考试) · China · Examination committee under the Ministry of Agriculture and Rural Affairs (MARA)
Original practice questions written to the published syllabus · not past papersDiseases of fish and crustaceans, the role of water quality, aquaculture biosecurity, and the residue rules for therapeutants used in food fish.
In the exams: NAVLE aquatics 1%; China runs a separate aquatic-animal category of its national exam
How our questions for National Practising Veterinarian Qualification Examination spread across the units of Aquatic Animal Diseases, Health Care & Management. Difficulty: 41 easy, 55 medium, 19 hard.
| Biosecurity in aquaculture | 14 | |
| Water-quality diseases | 13 | |
| Diagnosis of aquatic animal disease | 13 | |
| Parasitic diseases of fish and shrimp | 13 | |
| Bacterial diseases of fish and shrimp | 12 | |
| Therapeutants and residues | 12 | |
| Viral diseases of fish and shrimp | 10 | |
| Degree-day withdrawal periods | 10 | |
| Fungal diseases of fish | 9 | |
| WOAH-listed aquatic animal diseases | 9 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A laboratory reports un-ionised ammonia as 0.30 mg/L NH3-N. The permitted limit in the farm's standard is written as mg/L NH3 (as the whole molecule). What is the result on the standard's basis?
B. 0.36 mg/L NH3
NH3 = NH3-N × 17/14 = 0.30 × 1.214 = 0.36 mg/L. Multiplying by 14/17 (0.25) reverses the conversion, dividing by 17 alone gives 0.017, and leaving the figure unchanged ignores the different basis. The molecular mass of NH3 is 17 and of N is 14.
Further reading: Boyd & Tucker, Pond Aquaculture Water Quality Management; Emerson et al. (1975)
Fresh water at 25 °C holds 8.26 mg/L of dissolved oxygen at saturation. A pond at 25 °C reads 5.0 mg/L. What is the percent saturation?
A. About 61%
% saturation = 5.0 / 8.26 × 100 = 60.5%, about 61%. 165% inverts the ratio (8.26/5.0); 50% assumes saturation is 10 mg/L; 3.3 is the deficit in mg/L (8.26 − 5.0), not a percentage.
Further reading: Boyd & Tucker, Pond Aquaculture Water Quality Management; Emerson et al. (1975)
Which condition makes hydrogen sulphide in pond-bottom water more toxic?
B. A fall in pH
H2S is the toxic un-ionised form and dominates at lower pH, the opposite of ammonia, which becomes more toxic at higher pH. Higher DO oxidises sulphide, and alkalinity is not the determining factor.
Further reading: Boyd & Tucker, Pond Aquaculture Water Quality Management; Emerson et al. (1975)
For a laboratory investigation of a fish mortality, which animals are the best samples?
A. Live, moribund fish showing typical signs
Fish tissues autolyse within hours of death and secondary bacteria overgrow the primary pathogen; freezing ruins histology. Moribund fish give the best chance of finding the cause; a few healthy fish are useful only as comparison.
Further reading: Roberts (ed.), Fish Pathology, 4th ed.; Noga, Fish Disease: Diagnosis and Treatment, 2nd ed.
Farmed tilapia at 30 °C swim erratically in spirals, with exophthalmia and corneal opacity; the brain yields Gram-positive cocci in chains. What is the likely agent?
C. Streptococcus iniae or S. agalactiae
Meningoencephalitis with exophthalmia in warm-water tilapia and Gram-positive cocci points to streptococcosis. The other organisms are Gram-negative rods, and F. psychrophilum is a cold-water pathogen.
Further reading: Roberts (ed.), Fish Pathology, 4th ed.; Noga, Fish Disease: Diagnosis and Treatment, 2nd ed.
Crayfish plague is caused by:
D. Aphanomyces astaci
A. astaci causes crayfish plague, a WOAH-listed disease that devastated native European crayfish. A. invadans causes EUS in fish.
Further reading: WOAH Aquatic Animal Health Code, chapter 1.3; WOAH Manual of Diagnostic Tests for Aquatic Animals
Which one of the following diseases of carp and trout appears on the WOAH list?
C. Koi herpesvirus disease
Koi herpesvirus disease is listed. Columnaris, carp pox (cyprinid herpesvirus 1) and enteric redmouth are not.
Further reading: WOAH Aquatic Animal Health Code, chapter 1.3; WOAH Manual of Diagnostic Tests for Aquatic Animals
What does 'SPF' mean when applied to shrimp broodstock?
D. Free of specified pathogens, as shown by a defined surveillance programme
Specific-pathogen-free refers to documented freedom from named pathogens; it says nothing about resistance, which is what SPR (specific-pathogen-resistant) lines are selected for. Shrimp cannot be conventionally vaccinated.
Further reading: Lightner (ed.), A Handbook of Shrimp Pathology and Diagnostic Procedures
A cage was fed 1,500 kg of feed; biomass rose from 200 kg to 1,400 kg at harvest, and 100 kg of fish died and were removed during the cycle. What is the biological FCR (counting the weight of dead fish as gain)?
A. 1.15
Biological FCR = 1,500 ÷ (1,200 + 100) = 1,500 ÷ 1,300 = 1.15. The economic FCR, using harvested gain only, is 1.25. Subtracting the dead fish from the gain (1,500/1,100 = 1.36) is the wrong direction; 0.87 is the inverse.
Further reading: Standard aquaculture arithmetic
A pond of 0.2 ha with an average water depth of 1.2 m is to be treated with a chemical at a prescribed 0.5 mg/L. How much active ingredient is needed?
D. 1.2 kg
Volume = 2,000 m² × 1.2 m = 2,400 m³. Mass = 0.5 g/m³ × 2,400 = 1,200 g = 1.2 kg. Treating 0.2 ha as 200 m² gives 120 g; treating it as 20,000 m² gives 12 kg; ignoring depth (2,000 × 0.5) gives 1.0 kg. Pond treatments depend on accurate depth measurement — confirm against the product label and your national formulary.
Further reading: Boyd & Tucker, Pond Aquaculture Water Quality Management
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