Fish pond farming – dissolved oxygen, stocking density and growth
Design & TechnologyAgriculture, Forestry & AquacultureAges 12–13
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Agriculture, Forestry & Aquaculture
Cross-section of a tilapia pond: during the day algae photosynthesis raises dissolved oxygen, and at night fish and microorganisms respire and oxygen falls, reaching its lowest just before dawn. Students choose the stocking density, feed amount, aeration mode and weekly water-change rate, then press Run to watch the dissolved-oxygen chart for the last 48 hours, the fish mass over the days raised, and the survival rate. When oxygen drops below 3 mg/L the fish gasp at the surface and stop eating; below 1.5 mg/L they start to die — turning on the aerator or changing the water can save the pond.
Lesson: Raising fish in ponds: pond preparation, stocking, water-quality management, feeding and harvest
What it shows
Dissolved oxygen (DO) is usually the factor that limits how many fish a pond can support. The model balances four processes: algal photosynthesis adds oxygen in daylight and diffusion from the air adds a little more, while fish respiration and the decay of uneaten feed remove it day and night. DO therefore follows a daily cycle, highest in the afternoon and lowest just before dawn. Fish gasp at the surface and eat less below 3 mg/L and begin to die below 1.5 mg/L, so stocking density, feeding and aeration together decide growth and survival.
How to use
Begin with a moderate Stocking density, the Feed amount relative to ration at 100% and No aeration, press Run and watch the dissolved-oxygen chart over several days. Then raise the density and overfeed until the night-time minimum falls below 3 mg/L and the fish start gasping. Rescue the pond with Turn on aerator or Change water now, and compare final fish mass and survival rate under each Aeration mode. Increase the Playback speed to cover the whole grow-out period quickly.
Parameters you can change
- Stocking density 1–10 fish/m²
- Feed amount relative to ration 40–160 %
- Aeration mode No aeration, Aerator (on at night), Bottom aeration running all day
- Weekly water-change rate 0–50 %
- Playback speed 3–120 hours/second
Questions to explore
- At what time of day is dissolved oxygen lowest, and which processes explain this?
- How does feeding 150% of the ration affect dissolved oxygen, fish mass and survival compared with feeding 100%?
- Which aeration mode lets you stock the most fish per square metre without oxygen falling below 3 mg/L?
