Stocking a pond or tank correctly means matching the number and final size of fish to what the water volume can safely carry. Overstock and you get poor growth, disease, and oxygen crashes; understock and you waste capacity. This tool sizes the stocking number, maximum biomass, and daily feed from your volume, species density, and target weights.
How it works
The carrying capacity sets everything else:
volume = area × depth (or entered directly)
max biomass = volume × max density (kg/m³)
fish at harvest = max biomass / target harvest weight
stocking number = fish at harvest / (survival % / 100)
current biomass = stocking number × stocking weight per fish
daily feed = current biomass × (feeding rate % / 100)The maximum density you enter is the lever that depends on aeration and water exchange — the tool flags when that density is in the range that normally needs mechanical aeration so you do not silently plan beyond what the system supports.
Typical density ranges by system type
| System | Max density range | Notes |
|---|---|---|
| Static earthen pond | 1–5 kg/m³ | Natural oxygen supply only; limited by plankton bloom |
| Aerated earthen pond | 5–20 kg/m³ | Paddle wheel or diffused aeration required |
| Intensive tilapia tank | 20–40 kg/m³ | Continuous aeration + partial daily water exchange |
| Recirculating aquaculture system (RAS) | 40–150+ kg/m³ | Biofiltration, pure oxygen, high daily turnover |
These are illustrative ranges. Your actual safe density depends on your specific aeration capacity, water temperature, and species tolerance.
Worked example
Setup: 200 m³ aerated pond, target species tilapia, safe density 8 kg/m³, target harvest weight 0.5 kg, fingerling weight 20 g, expected survival 90%, feeding rate 6% body weight per day.
| Calculation | Value |
|---|---|
| Max biomass at harvest | 200 × 8 = 1,600 kg |
| Fish at harvest | 1,600 / 0.5 = 3,200 fish |
| Fingerlings to stock (for 90% survival) | 3,200 / 0.9 = 3,556 |
| Starting biomass | 3,556 × 0.020 kg = 71 kg |
| Day 1 daily feed | 71 × 0.06 = 4.3 kg/day |
| Daily feed at harvest biomass | 1,600 × 0.02 (grower rate) = 32 kg/day |
Feed demand rises dramatically as fish grow — build your feed budget around the harvest-season figure, not day one.
Common management mistakes
- Setting density based on volume alone without checking aeration capacity. A 1,000 m³ pond with no aeration cannot safely hold the same density as one with four paddle wheels.
- Using a fixed feeding rate throughout the grow-out cycle. Fingerlings need 5–10% body weight per day; growers 2–4%; pre-harvest fish 1–2%. A fixed rate over-feeds (wasting cost and polluting water) or under-feeds (slow growth).
- Ignoring survival in the stocking number. Mortality of 10–20% is normal; stock enough fingerlings to hit target biomass after losses.
- Not re-running the calculator weekly. Feed demand doubles as fish grow — weekly recalculation keeps feeding on track and avoids either waste or undernutrition.