dalmation mollies

Question
Hi Ron,
I have an established 70 litre tank that I
recently added some dalmation mollies too and
I've started having problems and I want to fond
out if it is down to the mollies as I now suspect.
I added the mollie with a few mollies, 2 angels
and a tiny catfish. All the fish appeared healthy
so I was shocked when 2 days later the catfish
and a molly    was dead in the tank. But I
assumed they was ill or stressed out too much
although I did my utmost to ensure they was
added to the tank safely and added stresscote
etc.
Today all of the fish was healthy and well. The
angel was lively and happy. During the day
noticed all of the mollies pecking at something,
I had already fed them in the morning so I
went to have a look at what they was doing
and was horrified to see them all chasing and
pecking at one of the angel fish.
After trying to scare them away from the fish
which didnt stop them I removed them all from
the tank and put them on their own in another
tank while I checked out the angel. Looked ok
but obviously was not well, other fish now was
picking at it also so I took it out and not
knowing what to do to help it the poor fish died
after a while.
My question is are the mollies killing my fish?
Do they kill healthy fish as well or was my fish
not as healthy as they appeared. Please help
me as I know many people with mollies and
they are not aggresive and I am
confused if mine are or not. Thank you.


Answer
Hi Leah,
 Any fish can be aggressive.  Basically a fish is aggressive if it wants something.  How effective it can be when it is aggressive depends on the opponents.  So for example, a molly is not going to try to do something against an oscar or a Jack Dempsey (both are large strong cichlids).  But a molly could easily be aggressive against a small angelfish.   It is a huge misconception in the hobby that a fish can be classified as "aggressive" or "nonaggressive" simply based on the species that it is.  Fish don't work that way (in fact, no animals work that way).  
Aggression is a function of the circumstances the fish is in and its ability to use its body to get what it wants.

Bottom line: yes it easily could be that your mollie attacked the other fish.

-- Ron
  rcoleman@cichlidresearch.com
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