Goldfish Bully

April 20, 2005 9:37 AM

How do I keep one goldfish from terrorizing another? I have two goldfish in a 5 gallon aquarium. They were the same size when I got them, but now one is bigger than the other. The big one bullies the little one.

The big one will follow the little one around and push him and peck at him for hours a time. The little one is missing scales (and sometimes there are scales floating in the water) and at times appears to be injured. The big one will trap him up against a rock and just peck at him until I tap on the glass and scare them both. This gives the little one a few minutes reprieve, but he's at it again soon enough.

I've tried throwing some food to distract the big one, but he doesn't even notice the food and also I don't want to condition them (are they smart enough to be conditioned?) that bullying the little one will get him fed.

I know that "stay out of it" would normally be the answer,and I would be happy to do that if the little one weren't being injured.

The water is clean and filtered. They're fed regularly and well treated.

posted by duck to Pets & Animals (15 answers total)

(re: conditioning) Everything can be conditioned. If you shock an amoeba and shine a light on it a hundred times, it'll start recoiling from just the light. So yeah, that might not be good.
posted by abcde at 10:07 AM on April 20, 2005

Can you separate them into two different tanks or divide the existing tank in a fish-safe way?
posted by safetyfork at 10:29 AM on April 20, 2005

Could you put some sort of screen across the middle of the tank (not the most aesthetically pleasing solution, I know) so that each fish has its own space? Or else could you use screen to box of a corner of the tank with an opening just big enough for the little fish, so that he has a place to hide?
posted by handful of rain at 10:29 AM on April 20, 2005

handful of rain, I like your style.
posted by safetyfork at 10:32 AM on April 20, 2005

There is no practical way to condition your goldfish, negatively or otherwise. Get the little one out of there immediately; he is being tortured.
posted by Specklet at 10:32 AM on April 20, 2005

Safetyfork--we are obviously of similar minds! Jinx!
posted by handful of rain at 10:41 AM on April 20, 2005

There are tank dividers you can get at the pet shop that might do the trick, although my experience with them is that unless you find out specifically for your tank size, they are a pain to get a good fit, and your fish will end up figuring out how to get to the other side.

You might try getting something that the little one can hide in like some rocks, or an overturned plastic flower pot with a small hole in it.

If you have tank decorations, rearrange them. This sometimes can upset the territorial nature of some fish, like cichlids. Not sure this is the problem here.

I think 5 gallons might be too small for them, though, even for two small goldfish. Can you get a ten gallon tank and put them both in there with some plants/rocks/hiding places? If the big fish continues to be a jerk, you can always move one back to the 5 gallon. Or just get another 5 gallon tank and split them up.
posted by drobot at 11:23 AM on April 20, 2005

the petshop told me 5 gallons was too small for two goldfish. i'm with drobot and specklet that you need to separate them into different tanks or double your tank size.
posted by crush-onastick at 11:36 AM on April 20, 2005

You could try adding hiding places, but a 5gal tank is small and bigfish will probably keep up the abuse. Get littlefish out of there. He won't mind being alone. Bigfish might be annoyed at the loss of a punching bag, but he'll probably forget in about 30 seconds anyway. They're not social creatures.

By the way, these guys get massive. I started with one tiny fish in a half-gal bowl with an air filter. Three years later I had four gigantic fish in a bathtub-sized tank with 150 dollars of wet/dry carbon water purifiers hanging off the back. Start trying to accommodate for goldfish, you won't be able to stop.
posted by cmyk at 11:37 AM on April 20, 2005

A five gallon tank for two goldfish is too small. Goldfish need more space than you think; ten gallons, minimum, per goldfish. Fish in cramped quarters secrete a hormone that stops all the fish in the tank from growing- that one of them has grown while the other hasn't is proof the tank is too small. You need at least a twenty-gallon tank. I can't guarantee that it will end the bullying, but it may well do so. At least there would be more room for the little guy to get away from the bigger one. There would also be room to make a rock cave (or an overturned flowerpot) to give the little guy a refuge.
posted by ambrosia at 11:40 AM on April 20, 2005

A larger tank will definitely help. If that won't fly, try rearranging the tank decor.

Goldfish Paradise is a pretty good forum for goldfish questions. But beware, they will flame you for keeping fish in anything smaller than a 10g tank.
posted by sid at 1:26 PM on April 20, 2005

Response by poster: Well I rearranged the decorations and that seems to have brought a (temporary?) end to the bullying.

But now I'm alarmed that my fish may not have all the water they need. Why do they need 10 gallons each? They're not that big and the pet store people (yeah, I know..I know) said it was more than enough, especially since they have good filtering, rather than just a bowl. Are they unhappy in there (when not being bullied?)? What's the danger to them?
posted by duck at 7:04 PM on April 20, 2005

duck, it's all about how concentrated the invisible fish effluvia is in the water. Goldfish are the dirtiest fish I've ever had. Very short gastrointestinal tracts, and they eat a lot. (Fish pee. You don't see it but they DO. Sneaky devils.) It's actually easier to keep a larger tank clean, since the nastiness won't be as concentrated and the filters and water won't need as much changing. There are test kits you can use to check the ammonia and nitrates present in the water.

If you've got normal fish-shaped fish (single tailed, torpedo bodies) they'll want room to swim. The more wobbly and funky types don't really have that problem.
posted by cmyk at 8:31 PM on April 20, 2005

Response by poster: I have fancy-tails. If I keep the tank clean will they be happy and healthy? You're right that they're little poopers, but I do change the water frequently. They seem happy...they like to play in the current and pick at their little rocks at the bottom.
posted by duck at 9:36 PM on April 20, 2005

This behavior sounds similar to breeding behavior I witnessed when I had a pond of goldfish. I'd never heard about it, but learned first hand. The male chases the female into shallow (eg, tops of plants) areas, looking like he's attacking. And spring was when this got going.
posted by Goofyy at 1:51 AM on April 21, 2005