Growth rate calculator (SGR)
Specific growth rate (SGR) is the average daily percentage increase in body weight between two weighings. Enter the average weight from two samplings and the days between them to get SGR, average daily gain and weekly gain, and project the weight a few weeks ahead at the same rate.
- SGR in percent per day
- Daily and weekly gain in grams
- Short projection at the same rate
- Runs in the browser, no sign-up
Calculate growth
The earlier of the two weighings.
The later weighing of the same batch or pond.
Calendar days from the first weighing to the second.
Up to 60 days. Assumes the same SGR holds, see below.
- Specific growth rate
- - % / day
- Average daily gain
- - g/day
- Weekly gain
- - g/week
- Projected weight
- - g
Calculations run in your browser. Nothing is sent or stored.
How is specific growth rate calculated?
SGR is the difference between the natural logarithms of the final and initial average weights, divided by the days between them, multiplied by 100. The result is a daily percentage. Fish sampled at 50 g and again at 80 g twenty-eight days later grew at an SGR of about 1.68 percent per day.
The logarithm is what makes SGR comparable across sizes. Growth in grams per day rises as animals get bigger; growth as a percentage of body weight falls. SGR measures the second, so a small fish and a large one can be compared on the same scale.
Average daily gain and weekly gain
Average daily gain (ADG) is simpler: the weight gained divided by the days, in grams per day. Shrimp farms usually talk in grams per week, which is the same figure multiplied by seven. Both are intuitive and both are size-dependent, so they compare well across ponds at the same stage and badly across stages.
Why the projection is short
SGR falls as animals grow, so projecting today's rate over a whole cycle overstates the final weight, and the error compounds. A projection a few weeks ahead is useful for planning the next sampling, the next feed order or a partial harvest. A harvest forecast over months needs a growth curve for the species at the farm's own temperatures, not a constant rate.
Growth only means something next to feed
A pond growing fast on too much feed and a pond growing slowly on too little can show similar SGR problems for opposite reasons. Growth between two weighings read together with the feed delivered over the same days gives the feed conversion ratio for that window, which is the pairing that separates a feeding problem from a health or water problem.
AquaOS computes SGR and a measured feed conversion between every two samplings entered against a batch, with the not-fed days excluded, so growth is read against the feed that actually went in.
Frequently asked questions
What is the formula for specific growth rate in aquaculture?
SGR (% per day) = (ln final weight - ln initial weight) / days x 100, using the average weights of the same group at two samplings. Use the natural logarithm, and average weights from samples large enough to represent the group.
What is the difference between SGR and ADG?
SGR is growth as a percentage of body weight per day, which makes it comparable across animal sizes. ADG is growth in grams per day, which is easier to read but rises as animals get bigger. Use SGR to compare groups at different sizes, and ADG or weekly gain to talk about a single pond with the crew.
How often should growth be measured?
At every sampling, between that sampling and the one before it. A running series of short windows shows a slowdown while there is still time to respond; a single figure computed at harvest only describes the cycle after it has ended.
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