[BlueSky99]

Last week we got 3 dalmation mollies, and were told we got 2 females and 1 male. I think one of the females might actually be a male, but I'm not sure. The same molly (the one on the bottom) sometimes shakes. Is that normal or should I be concerned? Sometimes I see the one who definitely is a male do that, but not as much as the other.

Also, the reason I don't know if that one is male or female is because while I don't see a fanned out anal fin, it has a short dorsal fin like the female (the male's is a lot bigger), but it has the same tail shape as the male .

 

[tankman12]

Not sure cuz picture is clear. The bottom one is impossible to tell for sure, cuz no fins to tell by. Top looks like a female, but again not sure.

Also clamped fins and shaking isnt a very good thing...
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[dancelady]

Can you post another pix?

From this pix, the top one looks to be a male, and the bottom a female by the SHAPE, not the fins. The bottom one has the rounded, pregnant look to it. But if you could take another pix, that would help me more.

All Mollies shake from time to time, also bump themselves on the bottom and flip off, and sometimes, just sit still in the water with only a tiny ripple of their fins. The shaking seems to not indicate anything but that they like to flutter, and I think they are resting when they are so still. A sick Molly will swim irregularly, like it has a problem, and will have a desire to hide away from the others. When you feed them, one that is not well will be hiding, won't rush to get the food. Swim bladder disease has them turning on odd angles, swimming in a peculiar off-perpendicular way to the normal level way of moving.

Dorsal and tail fins vary by the type of Molly and its ancestry. Some (which has sailfin ancestry) can have a larger dorsal fin, other are short-finned ones, and this is completely normal. Some have longer tailfins, especially if there are lyretails in their ancestry. Your male (top Molly) seems to have this in his background.

These are a few of the details on normal and abnormal behavior.

 

[Sylverclaws]

The chubby one is definitely female. The one that is thinner looks like it might be a different type of dalmatian and also looks female. However, that one is hard to tell on with that particular photo and could very well be male.

I'll give you some photos to tell them apart. Sometimes females have a heart shaped anal fin instead of a fan, males always have a pointed one though.


This is a male, notice that pointed, thin fin on his lower belly before the tail? That's his boy part. Not all males are shaped like him, but the male part should be the same for all livebearers.


This is a female, one of my more odd shaped ones, but you can see her anal fin is more fan-like.


Here's a female with a proper fan-shaped anal fin:



This one shows which fin is the anal fin with it circled so you know what I am talking about. =)


And another of my males, this one marked for you as well:

 

[Sylverclaws]

I knew I forgot something digging through all my photos....


Shaking. I have discovered the shaking is usually due to something missing in the water. Mollies are actually brackish fish, and whereas many can do pretty well in freshwater, some just cannot, and get the "Shimmies" which is called Livebearer Disease. Now...Try adding in a little salt for them. Small amounts at a time, a teaspoon per five gallons, then tomorrow add another teaspoon, and another the next day. After that, try to keep it that way. Go a little brackish, that should help your shimming friend. If it doesn't....well, what's your temp and tank size? Less than twenty gallons and it's too small for mollies and their high bioload, toxins in the water created by that high bioload can sometimes cause this to happen in more sensitive fish, in stronger ones on occasion too when it's high, so do a small water change before adding salt, dissolve it fully in water before adding it, even though they like salt, as with any fish, it can burn them added directly in.
Temp needs to be no lower than 78 degrees for them, though they prefer it around 80F. =) Mollies like it nice and cozy warm!

Check your water parameters, make sure you have no ammonia or nitrites, if you do, dose the tank with a bit of prime during water changes, you want low to no nitrates too but those are tolerable in smaller amounts. Make sure the water has high enough GH too, mollies like hard water. If things are too far off, it can cause all kinds of problems, including fungal infections and kidney issues.