The fish displays out the gill plates sometimes in the aquarium. To be honest, from the reseach that i ve consulted betta fish displays gill plates when they feel threatened around their environment and also to show hospitality. However, this behaviour happens naturally and it does not bring any harm for the fish. My betta fish has not show any signs of being sick. It has good apetite and it plays around its aquarium a lot. There has not been much change to the way it behaves despite what i ve notice lately. When i hold a mirror up to my fish it shows a cool action, but it does not last that long. This is probably caused by its reflection on the mirror, hence it gets aggressive when it feels threatend arond its environment. The betta fish swims around in circles and relax at tyhe bottom of the tank. I wish a tank was square or triaangular hape, this would cause a fish to not just swim arond but to also explore the corners of a tank. However, "Killer" is friendly and enjoys the small aquarium. It is pf essence to betta fish in small tank or plastic containers, because betta fish does not need strong flowing water in order for to survive