Your zebra danios are at the bottom of the tank because:
- Some zebra danios simply like the bottom of the tank
- They’re sleeping
- They’re stressed
If your zebra danios respond well to stimulation, swim actively, and have a healthy appetite, they’re likely okay even if they like staying at the bottom of the tank.
However, if they’re also behaving oddly, losing their appetite, or seem sluggish, they might be stressed. Many factors can stress out zebra danios, including poor water conditions, lack of food, poor nutrition, change of environment, incompatible tank mates, an overcrowded tank, or even loneliness.
If you notice them laying at the bottom of the tank, check their environment and living conditions immediately.