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Posted by Chris Lewis ·
A livebearer that holds its fins tight to its body and swims with a side-to-side wobble ("the shimmies") is telling you something is off. The good news: the most common cause is fixable once you test for it.
The usual causes, most likely first
- Water that's too soft. Guppies, endlers and mollies need hard water with minerals in it. Low GH and KH are a very common cause of shimmying, especially if you use RO water, rainwater, or live somewhere with soft tap water.
- Water quality. Any ammonia or nitrite, or high nitrate, causes clamping.
- Temperature swings from a weak heater or a cold room at night.
- Parasites or internal infection. Especially in new fish, and especially if only some fish are affected, they're losing weight, or they have stringy white poop.
What to test
Ammonia, nitrite, nitrate, pH, GH and KH. Strips are fine for a first look. Put the numbers into Water Check and it will tell you which ones are out of range for livebearers.
What to do
- If GH or KH is low, raise them slowly. Crushed coral in the filter or a mineral supplement made for livebearers both work. Aim for gradual change over days, not hours.
- Fix any ammonia or nitrite with water changes before anything else.
- If only the females from one batch are affected while your other fish are fine, and the water tests well, that points toward something they came in with. Isolate them and watch for weight loss or odd poop before choosing a dewormer.
Species care: guppy and Endler's livebearer.