Circling
Circling is a swimming behavior as opposed to the positional behavior of curling. It is very similar to whirling, but a circling fish has control of its movement. It swims purposefully in moderately tight circles in a limited area of the tank. It can be a sign of unilateral blindness, in which case the good eye will be to the outside of the circle. The blindness may be central or involve the eye. Circling also occurs with unilateral fin damage, and the behavioral change frequently becomes obvious before the 4n damage is recognized.
Flashing
Flashing describes a fish turning on its side and making a rapid semicircular swimming motion. In the process, the fish will usually rub against objects in the aquarium, including sand, gravel, or rocks. Flashing is a sign of an "itchy,, fish. Ectoparasite infestation is the most common abuse of this behavior, and a skin scraping and gill biopsy is indicated. In cases of severe gill parasitism, the flashing will be directed so that the impact with the substrate is to the opercular area rather than the back. Other signs of ectoparasitism include excess mucus production, and, in severe cases, anorexia.
Tail-walking
Tail-walking is a swimming movement in which the fish does not swim in a normal horizontal plane, but assumes an oblique position with the head directed toward the surface. The behavior is characteristic of tetras infected with the micresneridian Pleistophora. Abnormal positioning by the affected fish is due to loss of control over equilibrium, and it may appear to swim backwards as it attempts to correct its posture. Other behaviors associated with Pleistophora infection include continuous swimming, a failure to assume normal sleep patterns, and a lack of schooling activity. Definitive diagnosis of the disease is best achieved through histologic examination of muscle tissue.
