Molly Problem

[Sapphelah]

We have something funky going on in the tank. Monday we bought two silver lyretail molly females, one dalmation lyretail male and one female dalmation lyretail.
Our female dalmation died within two days after becoming very lethargic. She didn't appear to have anything wrong. We exchanged her for another (more pretty) dalmation lyretail female. The new fish was very energetic and playing and mating. Now suddenly she and only she is lethargic. None of the others have been affected in any way. They all seem fine and happy. Her eyes are clear, her scales are clear and normal. Her fins seem to be very relaxed-much like a human walking around depressed with their shoulders down, until someone prods her and she swims away. She stays down on the bottom of the tank just kind of chilling...
I ran out of test equipment, but it showed fine on Thursday. I'm unable to do anything as it's 10 pm here, and the lfs that tests for free is closed...
What can I do to help her?

 

[Sapphelah]

She's also swimming with kind of a "shimmy"

 

[ayasmansury]

I am no expert to these things but I would suggest that you add a little salt to your tank if that is possible, as I had one of my Molies do the same thing, I added salt and it worked, the shimmers went away in 2 days. The other alternative is to treat the fish for internal parasites, this too can cause shimmers and the fish turns lethargic, without any external visible causes.

Hope this helps.

 

[Lynda B]

You really should get yourself a home test kit, though. You can't count on a lfs to be there when you have an emergency. And sometimes, it could be that the test will give you immediately information on how to treat your fish.

Do you just add new fish directly to your community tank, or do you put them in an isolation tank first?

 

[SnBMeg]

As ayasmansury said, it is most likely a lack of salt in the water, though there could be other causes, as well.

Mollies are brackish fish, and require at least a small amount of marine salt in their water to remain entirely healthy. (Not table, rock, or "aquarium" salt, but the same salt that is used in marine aquariums.)

When I got my first mollies, I had no idea that they weren't freshwater fish. I had two deaths which I did not know the cause for. Some time after that I found this forum and its pinned topic on molly salt requirements, and have had no problems since (except for when a heater malfunctioned, but that's a completely separate issue.)

I even tried doing a small experiment: seeing how well a group of mollies would do in purely freshwater compared to some in only barely brackish water. The results were quite obvious, and convinced me to only keep them in brackish water from then on. Several days into the test, the freshwater tank mollies began flashing (the behavior you described as "shimmying") and a couple began to get small spots of fungus. Some of the fish were effected more than others, and some didn't show any negative response at all. But on seeing the fish generally not doing well, I made the water brackish again, and they were fine within an hour or two.

I keep my molly tanks just barely brackish, with a specific gravity of only about 1.002-1.003 (freshwater is 1.000, saltwater is something like 1.016-1.032+ (if I remember correctly; I've never kept saltwater tanks)), but even that small amount keeps them quite healthy. All it takes is a couple scoops from a bag of powdered marine salt, dissolved in a jug of water and added to the tanks with each water change. I purchased a cheap (about $6) plastic low-range hydrometer to measure the specific gravity/salinity after each change.