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

The glowlight tetra is an iridescent tropical fish named for its silver coloring and orange lightlike stripe. Glowlight tetras are much easier to breed when properly sexed, but sexing these fish can prove challenging. Frequently it requires that owners wait until the fish are adults.

Examine the size of your tetra. Female tetras tend to be bulkier than males. The size difference between males and females is significant enough that adult males look substantially thinner than adult females.

Watch your fishes' behavior. While males and females don't behave noticeably differently, males will behave differently if they are in a group with females. The males may chase and pursue the female, particularly when they are ready to breed. If you notice smaller glowlights chasing a larger fish, the larger one is almost certainly a female.

Look for an egg sac. Females develop eggs as they mature, and they will put on significant weight as the eggs develop. If you notice a whitish, puffy area along her stomach and underside, your fish is likely a female.


  • Glowlight tetras live in schools and will not behave aggressively toward one another. Thus there's no need to separate this species according to sex.

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About the Author

Brenna Davis is a professional writer who covers parenting, pets, health and legal topics. Her articles have appeared in a variety of newspapers and magazines as well as on websites. She is a court-appointed special advocate and is certified in crisis counseling and child and infant nutrition. She holds degrees in developmental psychology and philosophy from Georgia State University.