# A Community and Forum For Aquaponic Gardeners

Is there a scale (or rule of thumb) to estimate a tilapia’s approximate weight by knowing it length? I would like to look at a fish and say; that one is 12” long, so this fish is approximately X lbs. I want to avoid causing them undue stress.

Views: 1353

### Replies to This Discussion

NTS, that's a GREAT question! Everything seams to be listed in weight, but when I look at a fish, I think size. The next time we move our tilapia, I'm going to weigh them to see if I can put together a relatively reliable inches-to-ounces chart.

I can only tell aprox about the ones that are big enough to harvest since we often weight them after we kill them.

As for little ones.  It can be difficult to weigh a flopping struggling fish.

do not know how to make sub / superscripts here...

WT (lbs) =(CF x L (inches)n) / 1,000,000  where n is the exponent "3" for tilapia and CF = 750 to 900 for Tilapia

therefore if you measure a few and weigh them and input the numbers into this equation you will learn the CF for your fish.  CF is affected by numerous factors and can vary from time to time

this is from Recirculation Aquaculture,  Timmons, Ebeling

Marty, I seem to have a problem with the formula. If I have a 5 inch fish, multiply that length by 750, I get 3750 and raise that to the 3rd power, I get 52,734,375,000 and even dividing by 1 million gives a weight of 3,750 lbs - something is wrong, what am I not understanding?

marty lininger said:

do not know how to make sub / superscripts here...

WT (lbs) =(CF x L (inches)n) / 1,000,000  where n is the exponent "3" for tilapia and CF = 750 to 900 for Tilapia

therefore if you measure a few and weigh them and input the numbers into this equation you will learn the CF for your fish.  CF is affected by numerous factors and can vary from time to time

this is from Recirculation Aquaculture,  Timmons, Ebeling

Well, NTS, I just learned that the quick answer for Nile tilapia is 12" = 1 lb.

I just processed two Nile tilapia, each about 12" long.
They weighed on the shy side of 1lb.
We got 4-5 oz of meat from each.

This formula was pretty accurate: WT(lbs) = 800 x L(inches) / 10,000

Our meat weight (oz) was WT (lbs) / 16 * .33. I don't know if this would apply to all sizes, or if the percentage of meat changes with age.

I would better understand the formula if I knew what CF is. cubic feet??  That wouldn't make sense at 800CF.

Bill Barker said:

Marty, I seem to have a problem with the formula. If I have a 5 inch fish, multiply that length by 750, I get 3750 and raise that to the 3rd power, I get 52,734,375,000 and even dividing by 1 million gives a weight of 3,750 lbs - something is wrong, what am I not understanding?

marty lininger said:

sorry that my formula was not written clearly, the mistake is that only the length of the fish is raised to the 3rd power, then multiply by CF, then divide by 1,000,000  in this case a 5" fish at CF=750 weighs .094 pounds or 1.5 oz and at CF = 900 this fish weighs .11 pounds or 1.8 oz.

do not know how to make sub / superscripts here...

WT (lbs) =(CF x L (inches)n) / 1,000,000  where n is the exponent "3" for tilapia and CF = 750 to 900 for Tilapia

therefore if you measure a few and weigh them and input the numbers into this equation you will learn the CF for your fish.  CF is affected by numerous factors and can vary from time to time

this is from Recirculation Aquaculture,  Timmons, Ebeling

Sheri, the book does not define CF, it may simply mean "correction factor".  it is a useful tool however for commercial growers to gauge their feeding rate.  a fish with a low CF is skinny and not eating enough.  a fish in the high CF range is fat and is eating too much.  the ideal is in the middle if you can do it, according to my understanding.

Sheri Schmeckpeper said:

Well, NTS, I just learned that the quick answer for Nile tilapia is 12" = 1 lb.

I just processed two Nile tilapia, each about 12" long.
They weighed on the shy side of 1lb.
We got 4-5 oz of meat from each.

This formula was pretty accurate: WT(lbs) = 800 x L(inches) / 10,000

Our meat weight (oz) was WT (lbs) / 16 * .33. I don't know if this would apply to all sizes, or if the percentage of meat changes with age.

I would better understand the formula if I knew what CF is. cubic feet??  That wouldn't make sense at 800CF.

marty lininger said:

another thing Bill is that formula may only be meaningful for adult fish.  the book does not say.  the younger they are the faster they grow and since a younger fish is putting more energy into bone and skin than muscle as a percentage of body mass, the formula may just not work well for them.

Bill Barker said:

Marty, I seem to have a problem with the formula. If I have a 5 inch fish, multiply that length by 750, I get 3750 and raise that to the 3rd power, I get 52,734,375,000 and even dividing by 1 million gives a weight of 3,750 lbs - something is wrong, what am I not understanding?

marty lininger said:

sorry that my formula was not written clearly, the mistake is that only the length of the fish is raised to the 3rd power, then multiply by CF, then divide by 1,000,000  in this case a 5" fish at CF=750 weighs .094 pounds or 1.5 oz and at CF = 900 this fish weighs .11 pounds or 1.8 oz.

do not know how to make sub / superscripts here...

WT (lbs) =(CF x L (inches)n) / 1,000,000  where n is the exponent "3" for tilapia and CF = 750 to 900 for Tilapia

therefore if you measure a few and weigh them and input the numbers into this equation you will learn the CF for your fish.  CF is affected by numerous factors and can vary from time to time

this is from Recirculation Aquaculture,  Timmons, Ebeling

Ah, makes sense. And I missed the 3rd power. So...

Lbs = (CF x (In[n])) / 1,000,000

Lbs T =(825 (the perfect fish) x (12)) / 1,000,000

Lbs = (825 x 1728) / 1,000,000

Lbs = 1.4256

Hmmm... You may be right about the age, Bill. Ours weren't skinny, and were adults, but at 12", they aren't large adults. Our correction factor ends up at 556. We'll see what happens as the grow larger.

Regardless, this makes one think about how to plump them up more. It would be nice to get a larger percentage of meat off each fish!

I was guessing CF was Circumference

I took the liberty of paraphrasing Marty Lininger.

WT = CF x Ln / 1,000,000

Given WT is estimated fish weight in Lbs

CF is a correction factor 750-900 for Tilapia (varies with fish condition)

L is length in inches

n is an exponent which is "3" for Tilipia (maybe a body type indicator)

I use "open office", superscripts/subscripts are managed by the format Character function, which apparently is not supported by "Ning"

marty lininger said:

do not know how to make sub / superscripts here...

WT (lbs) =(CF x L (inches)n) / 1,000,000  where n is the exponent "3" for tilapia and CF = 750 to 900 for Tilapia

therefore if you measure a few and weigh them and input the numbers into this equation you will learn the CF for your fish.  CF is affected by numerous factors and can vary from time to time

this is from Recirculation Aquaculture,  Timmons, Ebeling