Instructions
Find out what type of fish you have. While some breeds may look similar, once you figure out Lily is a swordtail and Sam is a Molly, you’ll be able to see the differences.
Determine the gender. Many breeds, like the Siamese fighting fish, have distinct differences between the male and female fish, either in markings, fin length, fanciness or behavior.
Look for any other slight differences, like one with longer or thinner fins, one with a fatter belly or eyeball or differences in color, markings or body length or shape.
Watch behavior. If one fish continually comes blazing to the top of the tank when you feed and another lolls slowly up to the top and likes to hide in the plastic tank ornaments, you’ve got your differences right there.
Put them in separate tanks. If you still cannot figure out which fish is Lily and which fish is Sam, put them in separate tanks with name tags on the glass.
How to tell your fish apart
You have a gorgeous fish tank filled with 2 swimmingly glorious creatures. But you feel chintzy you cannot tell which fish is Sam and which one is Lily, although they looked much different in the pet store. You can tell your fish apart with some knowledge, a discerning eye and a few steps.