Fisheries
What the fisheries paper tests
The Fisheries section covers fish biology, pond and water quality management, hatchery practice, nutrition and aquaculture economics. Expect calculations on stocking, survival, yield, feeding rate and water exchange, plus questions on dissolved oxygen, pH, ammonia and carp breeding.
Core rules
- Stocking rate is fish per unit area or volume; expected harvest biomass = number stocked x survival fraction x average harvest weight.
- Yield per hectare is harvest biomass divided by pond area in hectares; convert m2 to ha by dividing by 10,000.
- DO is the first limiting factor; warm water holds less oxygen, and respiration peaks at night, so early-morning DO is the critical reading.
- Unionised ammonia (NH3) is toxic and rises with high pH and temperature; total ammonia nitrogen alone can mislead.
- FCR = feed fed / live weight gain. Lower FCR means better feed efficiency, but compare only at similar moisture and species.
Worked example
A 0.10 ha pond is stocked at 3 fish/m2. Survival is 80% and average harvest weight is 250 g. Expected yield? Area = 0.10 x 10,000 = 1,000 m2. Stocked = 3 x 1,000 = 3,000 fish. Survivors = 3,000 x 0.80 = 2,400. Biomass = 2,400 x 0.250 kg = 600 kg. Yield = 600 / 0.10 = 6,000 kg/ha. If the question asks for net yield, subtract the stocked biomass.
Traps
Multiplying by survival instead of applying it to stocked numbers; forgetting the ha conversion; reporting standing biomass as yield; treating total ammonia as toxic NH3; using FCR with weight gain in grams but feed in kilograms.