Fish Specific Growth Rate (SGR) Calculator
Calculate the daily percentage growth of your aquaculture stock accurately.
Daily Weight Gain: 0 grams/day
Biomass Multiplier: 0x
Understanding Specific Growth Rate (SGR) in Aquaculture
Specific Growth Rate (SGR) is one of the most critical metrics in fish farming and aquaculture research. Unlike absolute growth rate, SGR expresses the growth of fish as a percentage of body weight per day. This is essential because fish growth is generally exponential in the early stages; a 5-gram gain is massive for a 10-gram fry but negligible for a 1kg broodstock.
Monitoring SGR allows farmers to evaluate the efficiency of feed formulations, water quality conditions, and overall stock health. A declining SGR can be an early warning sign of disease, poor water quality, or underfeeding.
The SGR Formula
The standard formula used in fisheries science relies on the natural logarithm (ln) of the weights to account for the exponential nature of growth:
Where:
- ln: Natural Logarithm
- Wfinal: Final average body weight
- Winitial: Initial average body weight
- Days: The number of days between the two weigh-ins
Example Calculation
Let's say you are farming Tilapia. You stock fingerlings with an average weight of 15 grams. After 45 days of culture, you sample the pond and find the average weight has increased to 85 grams.
- Initial Weight (Wi) = 15g
- Final Weight (Wf) = 85g
- Time (t) = 45 days
Calculation:
ln(85) ≈ 4.442
ln(15) ≈ 2.708
Difference = 1.734
Divide by 45 days = 0.0385
Multiply by 100 = 3.85% per day
Interpreting Your Results
What constitutes a "good" SGR depends heavily on the species, life stage, and temperature.
| Life Stage | Typical SGR Range | Notes |
|---|---|---|
| Larvae / Fry | 10% – 30% / day | Extremely rapid growth, requires high protein feed. |
| Fingerling | 2% – 5% / day | Growth stabilizes; common monitoring phase. |
| Grow-out / Adult | 0.5% – 1.5% / day | Slower percentage growth, though absolute weight gain is high. |
Why SGR Matters for Feed Management
Knowing your SGR helps in calculating the Daily Feed Ration (DFR). If you know your fish are growing at 3% per day, you can adjust the total biomass estimate daily and increase feed accordingly to prevent underfeeding or feed wastage.
Factors Influencing Fish Growth Rates
- Temperature: Fish are poikilothermic. Metabolic rates and SGR generally increase with temperature up to an optimal point.
- Dissolved Oxygen (DO): Low DO levels suppress appetite and metabolism, drastically reducing SGR.
- Stocking Density: Overcrowding causes stress and competition, lowering growth rates.
- Feed Quality: The Protein Efficiency Ratio (PER) and digestibility of the feed directly correlate to SGR.