CorallineAlgae
Aquarium Advice Addict
Tanks aren't made to stimulate fish in this way. They are containment vessels. Any aspect of their construction that benefits the pets we keep are advertised as selling points. It's almost certainly a reflection and water movement response.
I've seen male bettas that will sometimes flair their gills at the glass in response to what they see as another male which is their own reflection. In cheap plastic "betta keepers" where there is no clear reflection they don't do this but when transferred to a different tank with reflective sides and no water movement I've noticed that they sometimes spend hours flaring. I've even seen people hold mirrors up to a "betta keeper" to get them to flair. Different fish react to their reflection differently. Some don't seem to react at all but swim through the currents.
I've seen male bettas that will sometimes flair their gills at the glass in response to what they see as another male which is their own reflection. In cheap plastic "betta keepers" where there is no clear reflection they don't do this but when transferred to a different tank with reflective sides and no water movement I've noticed that they sometimes spend hours flaring. I've even seen people hold mirrors up to a "betta keeper" to get them to flair. Different fish react to their reflection differently. Some don't seem to react at all but swim through the currents.