Like most of the other tropical fish, tetra fish also sleep. Although tetras are shoaling fish and are always in motion, when you turn off the lights, they show behaviors that resemble sleeping. Cardinal tetra,
How do I tell if my fish is sleeping?
It's pretty easy to tell when fish are sleeping: they lie motionless, often at the bottom or near the surface of the water. They are slow to respond to things going on around them, or may not respond at all (see some sleeping catfish here). If you watch their gills, you'll notice they're breathing very slowly.
Do aquarium fish sleeps?
While fish do not sleep in the same way that land mammals sleep, most fish do rest. Research shows that fish may reduce their activity and metabolism while remaining alert to danger. ... These periods of "suspended animation" may perform the same restorative functions as sleep does in people.
