Molly Activity

[Tarpan]

I have two Sailfin Molly's, one primarily white and one primarily black.

I have two questions about them...

1) They both spend a lot of time nibbling away at the gravel picking up stones and spitting them out. They do this even right after eating so I don't get the feeling it is a hunger thing...or perhaps it is. Is this normal behavior? It's kinda fun to watch.
2) One of them (the white one) has been keeping his dorsal fin down the last couple days. The water levels are all good, he's been eating well, high energy, I don't see any visible evidence of diseases, fins don't appear to be nipped at at all...just keeps the fin down. Should I be worried about this? It seems like a sign that he's not feeling well, yet I am not seeing any other symptoms. The black one still fans up his fin on a regular basis. I should also note that the molly's are likely only about 2 months old.


The tank is fairly lightly loaded at the moment with only the two molly's, a betta splenden, young pleco, and 5 zebra danios (40 gal tank).

 

[BIG BAD BARRY]

My mollies do exactly the same thing but dont always pick up the gravel. They even do it on the rocks and ornaments ant plastic plants.
Helps to keep tank clean of algae.
I may be wrong but livebearers tend to do this to supplement vegetable matter in their diet.

Fish will keep eating as much food that they find. I believe its instinctive behaviour from their natural habitat to eat as much as they can as they dont know when they will be able to locate food again.

Not sure about the fin aspect.

The fish should be active and performing when you approach the tank in the morning.

 

[OldMan47]

In a wild situation, mollies main diet is heavy in detritus, stuff you will find on the bottom. Picking at rocks, gravel and even the algae on the glass is a very common action for a molly.
The raised dorsal fin is a mating display. If you only have 2 juvenile mollies in a tank, it would not be at all unusual to see no mating display by at least one of them, if not both.

 

[Tarpan]

In a wild situation, mollies main diet is heavy in detritus, stuff you will find on the bottom. Picking at rocks, gravel and even the algae on the glass is a very common action for a molly.
The raised dorsal fin is a mating display. If you only have 2 juvenile mollies in a tank, it would not be at all unusual to see no mating display by at least one of them, if not both.

Well that's relieving.
The difference concerned me.

Good to know that I shouldn't be concerned in light of the absence of other symptoms.