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How to Tell if a Glowlight Tetra Is a Boy or a Girl

i shoal of fish image by Daniel Wiedemann from Fotolia.com

Knowing how to tell if your fish are boys or girls makes it easier to give them gender-specific names -- because Flounder and Dory just don't cut it. Male and female glowlight tetras are similar in appearance; both are brightly colored. You will need to wait until your glowlight tetras are adults to determine their genders because young fish are nearly identical, but there are a few ways you can tell which of your adult fish are boys and which are girls.

Step 1

Turn on the light of your aquarium hood so you can easily see small differences between the fish in your tank. If your hood does not have a light, turn on several lights in the room where you keep your fish.

Step 2

Measure your adult fish against one another. Females tend to be longer than males, so if one adult glowlight tetra looks bigger than several of the others, chances are good that she's a girl.

Step 3

Look at each tetra's belly. Male glowlights' stomach areas are less rounded than females of this subspecies, because the girls' bellies become bloated from carrying eggs when they are fully grown. Boy tetras usually have a much sleeker look than the girls.

Step 4

Watch how your fish interact with one another. If you notice a couple of your smaller glowlights chasing the larger ones around your tank, the smaller ones are probably boys and the larger ones girls.