Mollie Issues

When buying my first fish to put into my tank I purchased two Platies and 2 mollies (one silver and one black). Unfortunately, when I got home the black mollie had died, and I thought it must have been ill from the start. I returned to the LFS today and they offered me a replacement, so I went for another black mollie.

The silver mollie is constantly following it around and looks to be trying to have a good nibble on the black one at every possible opportunity. At first the black one didn't look too bothered, but now it is swimming away frightened each time. My new theory is that maybe the silver mollie killed my original black one in the bag.

Is this a common thign to happen, I'm not sure of the gender of the fish.

Any advice would be greatly appreciated, thanks.

What are the sexes of the fish?

theotheragentm said:

What are the sexes of the fish?

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I'm not sure of this I'm afraid . . help finding out would be great!

UPDATE: I have added a picture of the silver mollie, the black ones looks just the same, anal fin and everything.

what kind of dorsal fins do the Mollies have (fin underneath there body) if one thin one then a male but if theres two more typical fin shape ones then its a female

If you look at the anal fin (fin on the underside behind where the poop comes out) on the fish, the males have more of a tube-like fin, which is how they deposit their sperm. Females have more of what you would consider a "normal" looking fin, rounded in shape. If you have a male and a female, the male will constantly try to mate with her. You want to keep a ratio of 3:1 females to males for your first male and then 2:1 for every male after that. If you have two males, you are probably looking at mating aggression. Either way, you want to provide plenty of hiding places and items in the tank to block line of sight so the fish have somewhere to retreat in case they feel threatened.

Nick Bramley said:

what kind of dorsal fins do the Mollies have (fin underneath there body) if one thin one then a male but if theres two more typical fin shape ones then its a female

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Dorsal would be the one on top.

Yep, and also, mollies come in 2 (unofficial) kinds - there is the really peaceful ones that get along fine, and the other kind which can be pretty aggressive.
Mollies will also be much healthier in brackish conditions - it is not a must, but they will do better in it - read this thread.

If you are still wanting livebearers, I would go for guppies or platties.
HTH,
Rob

That picture is too blurry to tell. If it looks more like a triangle and not a tube, you're probably looking at female fish. While there are not really aggressive vs. non-aggressive types per se, some fish will have more aggressive demeanors than other fish. It's just a personality thing really. Give the fish plenty of hiding places and if that doesn't seem to work out, you might have to separate the fish.

Thanks for all of the advice, it is really appreciated.

I have just noticed, after feeding the silver molly doesn't look very happy. The dorsal fin isn't viewable (the fish has put it down) and every-so-often it looks like it is vibrating I can't believe that is normal behavior.

I know I keep asking a lot of questions, but I am quite concerned. Thanks.

I have been told the dorsal fin down means unhappy, but I have fish that do this all the time, and the rest of their behavior is normal. Watch for any other signs. The Silver Molly may just be full and relaxing, like humans do.

Back to the original issue, try to keep all female Mollies and Platies if you want peace and no babies. If you want babies, 3:1 ratio of females to males.

theotheragentm said:

I have been told the dorsal fin down means unhappy, but I have fish that do this all the time, and the rest of their behavior is normal. Watch for any other signs. The Silver Molly may just be full and relaxing, like humans do.

Back to the original issue, try to keep all female Mollies and Platies if you want peace and no babies. If you want babies, 3:1 ratio of females to males.

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Thanks