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Zebra danios (Danio rerio) are nearly impossible to sex when they are young. Once these fish mature, though, differentiating male from female is not particularly difficult. Because they are a social species, you should keep them in small groups, which happens to makes sexing easier -- unless they are all the same gender -- since you can compare fish with one another.
Examine the shapes of danios through the glass. Females tend to have rounder, deeper body shapes than their mates.
Compare sizes. Females tend to be larger. Note, however, than juvenile females will also be smaller than male juveniles.
Switch the aquarium light on, if it isn’t already, and compare colors. Males often have brighter, more luminous stripes than females.
Open the lid of the tank and observe the danios from above. At this angle, the females will appear “plumper” even if they are not carrying eggs.
Take a few pictures of your fish if you are still not entirely certainly. Other hobbyists on one of the Internet's aquarium fish forums should be only too happy to help you sex your danios.
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- 💡 Although they reproduce readily, it’s unlikely that danios breeding in a community tank will end up producing more fish than you have space for, mainly because adult fish including the parents will eat most of the eggs and fry. However, don’t take active breeding steps, such as separating the eggs, unless you are certain you have or can find space for all the resulting fish.Baby zebra danios are tiny; any survivors require a special diet -- they are much too small to eat adult fish food. Obtain a fry food for egg-layers from an aquarium supply store. Once the fry have grown a bit, crumble adult flakes very finely between your fingers for them and supplement with newly hatched brine shrimp.
- Aquarium image by crossgolfing from Fotolia.com