It will think that there is another fish really there and it will fight at it until you take the mirror away from it or it dies.
Placing a small mirror glass in front of your fighter fish will do the job
Put a mirror in front of it, that usually drives them mad.
The betta fish will see the mirror and then will be curious about it, because the mirror reflects the betta fish and they might think that it is another fish, so the fish will act differently.
ebay.com
A Siamese Fighting Fish can see its reflection in a mirror.
Not with many fish, although holding a mirror to a betta will cause it to flare its gills as it will think its reflection is competition
put a mirror in front of the tank if the fish bloats out its gills its a boy.
Holding a mirror in front of a fish can trigger aggressive displays as the fish may perceive its reflection as an intruder in its territory. This behavior is often observed in territorial fish species.
A fish eye mirror is a convex mirror
A male Betta should flash and square up to a mirror image of itself if it sees one occasionally. If the mirror is presented to the fish too often or permanently, the fish will simply learn to ignore it.
No, fighting fish (Bettas) are only interested in fighting with other fighting fish.
Heck no! I would highly discourage tanking common goldfish and Siamese fighting fish together. I have one of each myself, and they each have their own personalized homes and feeding/water changing schedules. Bettas are called "Siamese fighting fish" for a reason; the males are highly territorial and are fit to kill. A couple times a week I'll hold a mirror in front of my betta and he shows all his fins, and tries to attack his own mirror image. It is not good to do this for too long, as it will wear them out. Common goldfish are referred to as "feeder fish" because they make great meals for larger carnivorous fish. Though male bettas aren't very large, they are still carnivores.