What Are Fish Shimmies?
Fish shimmies are a symptom rather than a disease. Dr. Mollie Newton, DVM, in Columbus, Ohio, says shimmies are characterized by shaky swimming. This behavior may not be immediately noticeable in active species, like tetras, and it may come and go. Affected fish may shake, twitch or rock their body for short periods of time and otherwise swim normally.
Shimmying is an indication that the fish’s nervous system has been compromised. You may notice other behavioral changes such as:
- head shaking
- clamped fins (aka holding their fins closer to their body than usual)
- labored breathing
Changes to the fish’s physical appearance may also occur, but these can vary depending on the underlying cause of the shimmies. For example, fish who are stressed by high ammonia levels may also exhibit red streaks on the body and gills or cloudy eyes.
Because shimmying is a neurological response to stress, any fish can develop shimmies. There are, however, some fish who appear to be genetically predisposed. Livebearing tropical fish like mollies, platies, swordtails, and guppies are especially prone to shimmies, while other species like platies and swordtails may also be affected.
Some experts suggest certain livebearers are predisposed to shimmies due to the way they’re bred and raised. Fancy mollies, for example, are typically bred overseas in brackish conditions where both the pH and general hardness (GH) levels of the seawater are high. In the home aquarium, however, these fish are frequently kept in freshwater.
Keeping aquarium fish in water conditions that aren’t ideal for their species or that differ significantly from the conditions in which they were originally raised can cause severe stress. Over time, chronic stress can tax the nervous system and cause the fish’s body to break down. Shimmies can be an indication of this process.
