| Species | Model | Fish | Start (g) | Days | Temp (°C) | Feed % | FCR | Survival % | Expected final avg (approx.) |
|---|---|---|---|---|---|---|---|---|---|
| Tilapia | Feed-based | 100 | 20 | 60 | 28 | 3.0 | 1.6 | 95 | ≈ 240 g |
| Trout | SGR exponential | 50 | 40 | 45 | 14 | 2.0 | 1.3 | 98 | ≈ 105 g |
| Carp | Linear target | 200 | 15 | 90 | 24 | 2.5 | 1.8 | 92 | ≈ 220 g |
- Biomass (kg): biomass = (avg_weight_g × fish_alive) ÷ 1000
- Temperature factor: a smooth curve around an optimal temperature. It scales growth and feeding between 0.20 and 1.10.
- Feed-based model: daily_feed = biomass × feed_rate% × temp_factor, then daily_gain_kg = daily_feed ÷ FCR.
- SGR exponential model: daily_gain_g = weight × (SGR%/100) × temp_factor. Feed is estimated using feed = gain × FCR.
- Linear modes: weight increases by a constant daily gain (to a target, or user-defined), scaled by temperature.
- Pick a species and select a growth model that fits your data.
- Enter fish count, average starting weight, and projection days.
- Set temperature and adjust optimal temperature if needed.
- For feed-based mode, set feed rate and FCR from your feed label.
- For SGR mode, enter a realistic daily SGR from your records.
- Press Calculate Growth to view results above the form.
- Download CSV or PDF for logs, sharing, or printing.
Stocking density and space planning
Final biomass should match tank volume and filtration. Use the calculator’s optional m³ volume to estimate density in kg/m³. Many small systems stay manageable at 10–25 kg/m³, while intensive setups may run 30–60 kg/m³ with continuous aeration and solids removal. If projected density climbs quickly, shorten the grow-out, reduce fish count, or stagger batches every 2–4 weeks. Measure average weight from a 20–30 fish sample weekly for accuracy.
Temperature and dissolved oxygen control
Growth is scaled by a temperature factor around the species optimum. A few degrees off the target can slow feeding response and conversion, especially for trout in warm water. Keep dissolved oxygen stable, particularly after feeding, because low DO reduces appetite and increases FCR. Aim for at least 5–6 mg/L in most systems, higher for trout. Track temperature daily; stable conditions often outperform a warmer but fluctuating profile.
Feeding rate, FCR, and ration sizing
In feed-based mode, daily feed equals biomass × feed rate% × temperature factor. FCR converts that feed into weight gain; lower FCR means more gain per kilogram of feed. Example: 5 kg feed at FCR 1.6 supports about 3.1 kg gain. Start conservative, then adjust using uneaten pellets, water tests, and weekly sample weights.
Specific Growth Rate and target scheduling
In SGR mode, weight increases by a daily percentage, giving smooth exponential growth. Use records from your strain and season, and avoid unrealistic values; many warm-water species sit near 1.5–3.0% per day early, tapering later. Linear-to-target works when you must hit a harvest size by a fixed date, such as market day or system reset.
Budgeting harvest and feed inventory
The schedule outputs daily feed and cumulative feed, helping you plan purchases and storage. Combine total feed with cost per kg for feed budget, and multiply final biomass by sale price for revenue. Profit is a quick indicator, not a guarantee, so include losses, energy, water, and labor separately. Exporting logs supports audits, training, and repeatable batch comparisons.
1) Which growth model should I choose?
Use Feed-based if you plan rations from current biomass. Use SGR if you have weight‑tracking data and want smooth projections. Use Linear-to-target for a fixed harvest date. Use Linear daily gain when you know typical grams per day.
2) How do I estimate SGR for my fish?
Sample weights weekly, then compute SGR ≈ 100 × (ln(W2) − ln(W1)) ÷ days. Enter an average value for the period. If growth slows later, lower SGR or run shorter projections and compare batches.
3) What FCR value is realistic?
High-quality floating feeds often achieve 1.2–1.8 under good oxygen and water quality. Poor conditions can push FCR above 2.0. Start with your feed label or farm records, then refine using total feed used versus measured biomass gain.
4) Why does temperature change my results?
Fish are ectothermic, so metabolism and appetite shift with temperature. The calculator scales feeding and growth around an optimal temperature using a smooth factor. Large swings also reduce performance, even if the average looks acceptable.
5) How should I set survival percentage?
Use recent mortality history for your system and season. Small backyard systems often assume 90–98% if biosecurity is good. Lower survival reduces final fish count and biomass, and it also reduces daily feed needs in the projection.
6) Can I use the downloads for recordkeeping?
Yes. CSV works for spreadsheets and batch comparisons. The PDF is print-ready for notebooks, audits, or sharing. Save each export with a date and batch note so you can validate projections against measured weights later.