Calculating The Mass Of Fish

[fry_lover]

Obvously move to a different forum if this isn't to be in here.

I remember once reading a thread on here about calculating the mass of fish with regards to roughly how much ammonia they produce. I realise there are other variables (such as feeding routine and types of food), but i am sure someone on this site had an interesting forumla, something about multiplying the fish's length by girth or something to that effect.

I thought it was useful in regards to how to stock, for example a Blood Parrot fish could be 5" and a Rainbow Fish could be 5", but in terms of total output of waste/ammonia the Parrot is higher as it's basically a more "bulky" fish.

So for example i know to stock a tank with x10 "bulky" 6" fish would cause more waste than x10 "slim" 6" fish, but i just wanted to get a bit more exact with the science of it if possible

 

[JustKia]

A simple but not particularly accurate method is to assume the fish is a box and multiply length x width x depth of fish. Obviously a fish isn't a box and this method over calculates the size of the fish, but in such circumstances it's probably better to over calculate than under.

A more accurate method would be to put a known volume of (tank/dechlor'd) water into a suitable container then carefully add the fish and measure how much water is displaced.

 

[reportingsjr]

The most common way to get the volume of objects in general is to do as aforementioned, place it in a certain amount of water and see how much is displaced. The same method can be done to measure the mass. Get container with water (tank/dechlor'd) and measure the mass of it, then place the fish you want to know the mass of, place it in the water and measure again, then simply subtract the two values and you'll get the mass of the fish!

Simple enough, eh?

 

[Bignose]

It's not that simple, though. Because the fish is going to be moving around in the body of water, the water surface is going to be moving up and down and back and forth. It isn't going to be very easy to read the level of the water. Similarly, with the fish sloshing the water around, the scale isn't going to remain steady (just like swaying on a bathroom scale). It isn't super easy.

The best method I think would be to use a series of photographs and compare with the sizes of known objects. Computers can do this, though it will take many photos from many different points of view. Then, I'd just use the density of water and multiply by the calculated volume of the fish to estimate the mass.

http/www.fishforums.net/index.php?showtopic=243855 This is an old thread in which I estimate how much mass a school of tetras produce. It has lots of assumptions, because every step along the way has lots of specifics that can change the final result a each a little bit, but all-in-all I think that the estimate is pretty good.

 

[fry_lover]

thanks everyone, food for thought!

 

[ScottyBoy]

The only way is to do it is take 3 weighs for a week 3 everyday, so thats 21 weighs find the average and do this every fortmonth and find the average weight this could also help in calculating fish growth and witch conditons,lighting and foods stimulate growth the most in a fish or even to see what foods are right for your fish.