Mollies Killing Other Fish

[claireyscott]

We introduced 5 dalmation mollies into our tank around a week ago and they were fine until yesterday evening. Then yesterday they began systematically attacking everything else in the tank. They managed to kill a blue gourami and left to 4 inch Silver sharks fighting for their lives. Needless to say we have isolated the mollies for the time being to give the other fish chance to recover.

I think that one of the mollies is pregnant and I'm not sure if thats whats causing them to be so aggressive. Any advise would be great as to what to do, how long to isolate them for, anything really!

Thanks again

Claire x

 

[Davo86]

Hi claire, what is the ratio of Males to females?
Also what size tank are they in and how many tankmates do they have?
Are all water stats ok?

 

[claireyscott]

Hi claire, what is the ratio of Males to females?
Also what size tank are they in and how many tankmates do they have?
Are all water stats ok?

I think that there are 3 females to 2 males,

They are in a 50 gallon tank with

2 Silver (Bala) Sharks
A red finned shark
A bristle nose catfish
An elephant fish
2 blue gouramies (One of which they killed last night)

Not sure about water stats, will check those later today

Thanks

Claire

 

[claireyscott]

One of the sharks that was attacked over night has now died, the other is looking pretty sick too. My hsuband has just said that the one that died has chunks missing from it where it's been attacked. The other fish in the tank: A red finned shark, another blue gourami, (same as the one killed last night) elephant fish and bristle nose are apparently all looking healthy. This is begining to worry me, don't want to get rid of them but not sure what else to do.

 

[Athena]

Hmmm...strange - I know that my two dalmation sailfin mollies can get extremely possessive over food and can get quite bullying - but I've never known them to actually take chunks out of another fish or cause any actual harm, it's usually just chasing and a bit of nose-butting.

Did you actually see the mollies attacking the sharks? Just wondering because you say you have a red-finned shark in there - I know that the rule of thumb is not to mix different species of shark in the same tank as they will attack each other and cause deaths. If it's a large tank then sometimes you can get away with it as they will each claim a section of the tank as their territory and only fight when that is invaded.

Could it be that adding the mollies to the tank has upset the territorial boundaries a little, that both sets of sharks then had less of a boundary and it's caused some unrest in the tank?

Athena

ps - In your post on the other forum thread you say your tank is 25gallons, was that a mistake?

 

[drobbyb]

What size tank? If fish are crowded they can become agressive to the point of killing other fish.

On another thought, if your tank is indeed 25 gallons, it's way too small for silver sharks. They can get to 14 inches long.