Fish Suddenly Aggressive

Question
QUESTION: I have a 30 gallon aquarium with 2 small angelfish, a couple of balloon mollies, and a couple of diamond tetras, and two cat fish.  

Last week, the pump on one of my other tanks broke. It is a specialty pump that had to be reordered. Since the ammonia level in that tank was rising, I had to temporarily add those fish into my 30 gallon tank.

The fish I added to the 30 gallon were 2 guppy's, 2 neons, and 2 lyre tail mollies.

The next morning, one of my angels was dead. I didn't see any sign of injury, so I didn't think much about it. Went out and bought another angel, the next morning, it was dead.

I got another angel. A few hours after putting the angel in the tank, we found the other fish going at the angel. (Nipping, etc.) The angel is obviously injured. I removed it from the tank. Hopefully it will be ok.

I never had any problem until I added the fish from my broken down tank. We noticed that all of the fish except for the angels have formed a "school" they stick together and dart all over like crazy. The also do seem to be play nipping at each other at times. Even though they stick together.

I was wondering if since they formed a "school" does this make them agressive? I don't know what to do. I am afraid that even after my new pump is here, fish removed, that my other fish will still be agressive.

So basically, I need help with this agression issue. Thank you so much!! I really don't know what to do. I have never had this problem before.

ANSWER: Hi Jen

It's likely the stress that killed the Angels, rather than an injury. Sometimes stressed Angels actually appear to be dead by laying on their sides on the bottom of the tank. Sometimes they recover, sometimes they don't.

I'm not sure what type of pump you would have that has to be ordered. There is no specialty pump that would be needed for the care of Lyretails, Guppies and Neons. I've had power filters go out and have bought other ones at the fish store. So without knowing the type of equipment you are using, I'll give you the best solution I can with what I do know.

Lyretails, especially males, are known for aggression. Especially toward slower fish such as Angels. This is also true about Balloon Mollies. Male Guppies are commonly aggressive toward each other rather than other fish. I haven't known or heard of Neons or Diamond Tetras to be aggressive to any fish. When Angels are large enough, they will eat Guppies and Neons. I also haven't known 2 fish of a species or multiple fish of different species to form schools. However, forming schools usually calms fish down rather than making them aggressive.

If you just have one or two Angels, I would move them to the tank that broke down. You can go to the petstore and get a hang on back power filter large enough for that tank. There should be enough beneficial bacteria in that tank to allow a new filter to handle the ammonia and prevent a cycle process from starting over. When the new pump arrives, having an extra filter in that tank would be beneficial and not do any harm.

Mollies and Guppies shouldn't be together. Angels, Guppies and Neons shouldn't be together. Since I think it was likely the Mollies attacking the Angels, it would be best to keep the Guppies with the Mollies rather than keep the Mollies with the Angels. When the new pump arrives for the other tank, you can move the Angels back to the 30 gallon and move the Mollies, Guppies and Neons to the other tank.

This is about the best solution I can give you without getting a 3rd tank for the Mollies. Hope this helps, good luck!

Richard



---------- FOLLOW-UP ----------

QUESTION: Thank you for your reply. Oh yes, they are all schooling. I have never seen that either. (Various species schooling.)I do have another question, what about the diamond tetras? Should they be moved too?

Answer
Hi Jen

Hmmm that's interesting to know. I'll have to research that one, I've never experienced it or heard of it before.

As far as the Diamond Tetras, they can be kept with the Guppies, Neons and Mollies, or left with the Angels. There isn't any fish you have that would have trouble with the Diamonds.

Good luck!

Richard