do fish know not to eat food rotten food?

[venzi]

So if left over food remains in the tank.  Do fish still end up eating the food after it goes bad (spoils/rotten) or do they know the taste of rotten food and spit it back out?

[Biotope Biologist]

They know what’s bad and what’s not and will spit it back up.

 

Although I leave frozen foods in for a day and the fish pick at it as they feel hungry. 

[BlueLineAquaticsSC]

The bigger issue to worry about is water quality. In the wild fish eat what they eat, sometimes fresh sometimes not so much. Their are even organisms that only eat rotting stuff, like detrituvors (not sure if that’s a real word). In a fish tank tank rotting food is going to equal ammonia and nitrate spikes