science

I'm always a little skeptical of anyone who denies conciousness / sentience to animals. We all do stuff based on stimuli.

Also there are layers to conciousness. If you want to make an argument that a fish doesn't have the same level of higher thought as a human I would agree with you depending on the type of fish, but to assume something operating on a more base level isn't having their own version of a concious experience is arrogant. Just because we don't have perfect empirical evidence does not mean it's not happening; we may need different measuring devices.