Re: What is the best way to mass a group of six goldfish?

I presume you would like to temporarily immobilize your fish so you can 
weigh them.  I can think of three ways to do this:

1.  In our lab, we temporarily immobilize fish by anesthesizing them using 
a solution of 3-aminobenzoic acid ethyl ester.  This compound can be bought 
from Sigma Chemical Co. (Item A-5040).  Make a stock solution of 1 mg/mL, 
and add drops of your stock solution to the fish in a small volume of water 
(~150mL) until they roll over and slow their gilling.  Then remove them 
from the water, weigh them on a piece of paper, and quickly return them to 
their tank.  They should recover within a few minutes.

2.  Put a small and lightweight plastic cup on your scale with about an 
inch of water in it.  Add the fish to this cup one by one and measure the 
difference between the weight of the cup with and without the fish.  This 
method will be the simplest way but also less accurate.

3.  Remove fish from tankusing a net, and place them on the scale to weigh 
them.  Since they will still be very much awake, they will probably flip 
off the scale quickly, so you would have to note their weight quickly.