The number of fish you can put in 50-liter aquarium is 16-17. The general estimation is 1 liter of water for 1 centimeter of fish.
Suppose your fishes are 3 cm in size. Follow the steps to count the number of fish:
Note down the volume of your aquarium in liters.
Estimate the size of your fish in centimeters.
Divide the volume by the size.
The result is the number of fish.
So, 50/3 = 16.66. Round this result to 17 because you can't have half a fish.
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