How To Know If A Danio Fish Is Going To Spawn
Danios are small schooling fish. There are many different breeds, with different colors and patterns, and many of these breeds are very popular with aquarium hobbyists. Although there are some types of fish that are hard to breed in an aquarium setting, danios breed well on their own. If you suspect your female danio may be ready to spawn, it's important to find out for sure, so that you can prepare the tank for the baby fish, called fry.
Make sure the fish you are looking at is actually a female. Male and female danios look very much the same, but if the fish in question turns out to be male he could actually be having some serious health problems. Female danios are generally fatter than male danios, whether they are carrying roe or not.
Look at your female danio. If she looks wider than normal, she is probably carrying roe. Since danios are not livebearers and female danios never carry fertilized eggs, this is as close as danios get to being pregnant. If your female is carrying roe, your male danio will fertilize the eggs as they are dropped, during spawning. Watch your fishes' behavior. Danios like to spawn in the mornings.
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Warning
Danios will eat their own eggs not long after they have laid them. If you want the danio eggs to hatch, you will have to keep the parents from the eggs. You can do this by laying marbles or a loose-weave net over the bottom of the tank. The eggs will fall through the gaps in these materials and the parents won't be able to reach them. You can then remove the parents from the spawning tank into a different tank. You can also remove the eggs from the tank with the parents in it, but this may be slightly trickier.