i had a 3ft tank full of guppies and fry i thought i caught all the fish in the tank so i drained all the waterexcept for about 1 cm above the stones and then took the tank outside and left it for a few days and then went to clean it out and saw movement in the water there was still atleast 10 -15 guppy fry and 3 adults in there the temp in the tank was only 5 or 6*c and they are still alive