Aggressive Rasbora

A

amndbrk1

Registered Member
Nov 19, 2005
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Hi, my husband and I recently got a 29-gallon aquarium. He has had aquariums as a teenager and a child, but I have never had anything over a 1-gallon aquarium. Although he’s had aquariums in the past, we are both novices at this and are enjoying it tremendously.

Here’s the problem…

We have 2 Harlequin Rasboras. One is very pleasant and good with the other fish, and the other is quite aggressive. He was one of the first fish we brought home, and on the first day, he chased the other rasbora around and nipped at her for hours. I was concerned, because I wanted everyone to “play nice,” but my husband said not to worry about it, that they were just playing. He has calmed down a bit, but still chases and nips at the other fish a bit, not just the other rasbora, all of the other fish. I might add that he is the biggest fish in the tank (about 3 inches). I will list our other fish at the bottom of this post in case you need to know. I have been wanting to give him back to the pet store since the day we got him, because he seems to aggravate the other fish.

Here is my main concern:

I am very upset, because I just found one of my fish (a beautiful hifin sunburst platy) dead at the bottom of the tank with her entire tail and her fins eaten off. It was quite disturbing to me, I guess because I didn’t expect it. Last night, I caught the rasbora chasing the platy all over the tank. It was the worst that I had ever seen him act. They were swimming extremely fast, zipping from one side of the tank to the other. She was really scared, I could tell. After this little episode was over, the platy hid under a cave/rock in the aquarium for the longest time. This was very unlike her. My husband said, “she is really traumatized from that chase, maybe I should try to get her to come out.” I said, “no let her stay under there, if she’s scared, chasing her out isn’t going to help any.”

So, I’m trying to figure out what happened.

My first instinct was to blame it on the Rasbora, but I’m not sure if it’s really possible that he killed her. I do feel like what happened yesterday with the chasing does relate to the death of the platy, however.

I’m thinking maybe that the death of the platy was not a result of the chasing episode or the aggravation from the rasbora, but that the reason the rasbora was chasing her yesterday was because perhaps he could tell she was sick/weak and was picking on her for that reason. ??? Then today she passed away and he (and the other fish) ate her tail and fins, which I understand is normal, I just don’t like it.

I guess I just want to know if it is possible that he did somehow kill her, because if so, I need to get rid of him before he does it to another fish.

Sorry if this seems ignorant; I am very new to all of this.

Our fish:
2 female guppies
1 male guppy
1 molly
1 hifin platy (not anymore)
1 red wagtail platy
2 Harlequin Rasboras
3 zebra danios
6 neon tetras
2 pleckos
1 snail

Thank you very much!
 
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Is it possible that the rasbora killed your platy? Yes. Is it likely? No. Harlequin Rasbora are tiny fish with a mouth to match. Though, it is quite rare to see a really aggresive rasbora, it can happen. Your next step would be to single out the cause of your dead fish to one or two likely situations. You may never know what happened for certain, but you can take a pretty well educated guess. First things first I would take a sample of your water to the fish store that you bought the fish from. Most of the time they will test it for little or no money. If your water tests out fine, you can scratch that off the list of culprits. Next you may want check your aquarium for disease. Ich or other parasitic or bacterial diseases can go unseen to the untrained eye untill it is too late. Google "aquarium fish diseases" and you should find plenty of information and how to go about treating the disease if you have one. Another very possible scenario is that your platy may have been pregnant (only of course if its female). Fish as do any other animals become weaker while pregnant. The stress of the rasbora simply chasing her around the tank may have been too much for her to handle.Though you may have only had female platys in your tank it is still very possible for your fish to be pregnant. If the fish was mixed with male platys at the place you bought it from it may have gotten impregnated there. The female can continue to bear young even after there is no male in the tank. As most aquarist learn, the best way to prevent deaths in your aqaurium is to keep a close eye. Observe your tank (especially the rasbora) and make sure he is not harrasing any of your other fish. If you see him nipping other fish to the point where you feel uncomfterable you may want to return him or get a isolation tank for him. Be patient and do a little reading, you'll get the hang of this hobby in no time! Welcome to the wonderful world of fish keeping!
 
I have 9 rasboras in my 40 gallon. 5 Golden Rasbora's and 4 Harlequin. I have never seen the slightest bit of aggression amoung them. Their tank mates are 5 rummynosed tetra's, 7 neon's, a small wild guppy male, 4 albino cory cats, and a male betta and all get along fabulously.

Perhaps you should try adding more Rasbora's. They really like to be in larger schools than 2 and that could spread some of his aggression out. Seriously consider adding more. I have never seen any of mine act even mildly aggressive.

If it is a fish...I would seriously consider the zebra danio's as a culprit or the molly's. In my experience the zebra danio's are nippy nasty critters (they nipped and harrassed a male betta quite litterally to death and my personal experience leads me to dislike them strongly) or even the molly. Molly's can be quite un-even tempered at times.

I agree whole heartedly with secretmuscles. Observe your tank...watch what is going on and then keep in mind that a lot of aggression happens after lights out.
 
I aslo have four harlequin rasboras in a 10 gallon with a betta and 4 Corys....never have seen any aggression at all ....are you sure you have a Harlequin rasbora? I didnt think they got that big...3 inches?
 
I have witnessed aggression in rasboras... here is a thread that I posted about my aggressive rasbora. I only had two rasboras at the time and the aggressive one was significantly larger than the other one. Even though there is the occasional chasing, and the shaking, the problem was largely solved by increasing the size of the school.
 
knashash said:
I aslo have four harlequin rasboras in a 10 gallon with a betta and 4 Corys....never have seen any aggression at all ....are you sure you have a Harlequin rasbora? I didnt think they got that big...3 inches?
Click to expand...

I wondered about the size too. I didn't think they could get that big either.

Are you sure it's a Rasbora? Most stats I've seen them listed at is maximum size of 2 inches.
Here is a link with pictures of Rasbora's
http://www.liveaquaria.com/product/scateg.cfm?pCatId=887
 
Do you have test kits? I would get your own ASAP and in the meantime, take a water sample to your LFS and get some exact numbers for ammonia, nitrite, and nitrate. Those are always helpful to know when there are issues in a tank:). If the platy was weak at all, the other fish will very likely take advantage of that. And almost all fish will snack on a dead/dying fish, so the rasbora might have had some help that you just didn't see.

I noticed in your list of fish you have 2 plecos? Do you know what kind they are? The common plecos that most people get are huge poop machines, and easily get over 18 inches. Unless you plan on a serious tank upgrade you should consider returning them. Most stores will not take them back once they get any size to them, because they are a dime a dozen :o

As long as your tank is cycled (0 ammonia/nitrite, and a reading for nitrate) I would suggest a few more danios and rasboras. They'll both do better in larger groups, and it should help the rasboras with any aggression
 
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