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I originally got 2 rainbowfish (m. splendida) along with 2 rosy barbs for a 29g tank. The larger of the rainbowfish (heretofore know as the tyrant) spent a lot of its time making sure the other one just stayed in a corner behind a plant, although the other one was assertive enough to eat and be a little defiant.

I recently added 4 smaller rainbowfish of the same kind since I'd read they like to be in groups of at least 6. One of the new rainbows was obviously ill when I put him in the tank and died the next day leaving 5.

These new fish were similarly sent to a corner of the tank. This went on for a couple days. I thought things had improved some since the tyrant seemed to be allowing them all to venture out of the corner a little.

However, when I fed them today, I noticed that the 3 new fish are barely able to get any food because the tyrant chases them away. One gets food that's falling, but the other two seem unwilling to grab falling food. When they try to go to the surface for food they're rammed by the tyrant and they go off and hide. The same goes for the other original fish, but s/he doesn't care and keeps going anyway.

I know nature can be unpredictable, but I didn't expect this kind of harassment. Does anyone have any experience with this kind of behavior, especially in rainbowfish? Am I just worrying too much?

As you can probably tell, I'm new to fish. I didn't realize it was going to stress me out so much.

Thanks for any info you have!

I'm relatively new also. I can share a bit, and also ask a few questions that might help others with more knowledge help you.

First of all, do you know what kind of rainbowfish you have? Secondly, do you know what sexes the various fish are?

I bought some dwarf neon rainbowfish (also called praecox rainbowfish) and have never seen serious harassment. I have two males and three females. The two males will occasionally chase each other a bit, and also flare their fins at each other, but never to the point where the "loser" retreats to a corner of the tank. 95% of the time they group together and seem happy in each other's presence. At feeding time, each (even the alpha male) goes crazy over the food and completely ignores the others.

Unless things settle down, I suspect you may have to get rid of the one that is bothering the others--otherwise the stress will make them very susceptible to disease and you may lose the whole batch.

Thanks JohnPaul for the reply. These are Melanotaenia splendida...I know there are lots of variations on this one, but that's as specific as they got.

I now think the problem is a combination of the one fish that is overly aggressive and the new fish being sick. Hard to know which is more responsible. A second of the new fish died yesterday.

I haven't quite decided what to do at this point. I may just take all of my 4 remaining rainbowfish back, original and new, and regroup.

Thanks again.

Oh, I forgot, after a lot of looking the other day, I believe there were 3 males and 2 females. Now it's 2 and 2.

I don't know. The only chasing I would call common in Rainbowfish is when a male is trying to induce a female to spawn. They will chase other males away from the preferred spawning site but its never that nasty. Fish have their own personalities. You might have just gotten a really aggresive bully.

I ended up taking the aggressive fish back to the store after two of the new fish died. Unfortunately, the other two new fish died within 3 days after that.

I now believe that the 4 new fish were ill when I got them. Looking at the place I bought them, either they've been selling a lot of rainbow fish or they're all dying. I think they went from 50 fish down to 5 in 2 weeks.

Now I'm nervous that whatever they had might be passed on to my 1 remaining rainbowfish and 2 rosy barbs.

I really see now why people have quarantine tanks!

Firstly, when you bought the rainbows how big were they? How did they look? skinny? pale? Did they have cottonmouth?

If the fish were sick or stressed in the tank they tend to hide a lot. My Splendida are a boisterous family, all of which have amazing colour (except the female) and are very healthy. They do get stressed in small tanks with little cover.

How big is your tank, and how new is it?

Thanks for the reply. I have a newly cycled 29G tank and the only other fish in there are 2 1.5" rosy barbs which totally mind their own business.

The original 2 rainbows were a good 2" when I got them. The 4 new ones were a good deal smaller, maybe 1", had good color, didn't seem skinny, and didn't have any visible abnormalities. They just hid a lot and just didn't seem to have any energy (to eat, avoid the aggressive fish, etc.) I think the problem was really more with their being sick than with the aggressive fish.

I'm down to just the one rainbow right now having brought back the aggressive one (which I now regret) wrongly thinking I could still save two of the remaining new ones. This fish has taken to hanging out with the two rosy barbs. A little sad, but she seems to be otherwise fine. I think I'm going to have to get brave and get at least a couple more at a better store.

Give it time, and see what happens.

I was worried about some of my rainbows till they got fed and had some energy, they were being bullied by one but now he's not so tough