I would re home the fish, all goldfish get big though the common,wild type is the biggest, at 24 inches and 5 lbs max size. yet even the mutated egg shaped ones, orandas and fantails get big, (ever see a grapefruit with fins?"), under the right condictions, its probably a stress related behavior, the chasing around the tank. You ARE believe or not, surprising good when it comes to "keeping goldfish" Most goldfish are doomed to die in that infamious prison- the goldfish bowl. Also Goldfish can live for a very very long time if kept right, Tish the world record, for the worlds oldest goldfish lived to 43 years old !

How large, in length, are the fish?

The harrassment from the calico will only cause more stress and eventually cause an injury which will lead to an infection, then death.

If the fish are small then you can add lots of plants, real or faux, to the aquarium so the larger fish has somewhere to hide.
You don't have to use aquariums to overwinter them. Nearly any large container can be used. I've kept them in kiddy pools (the hard plastic type), muck buckets and horse watering tanks. I'd either get them into a larger container with the plants and rocks for the fish to hide in, or give them each a separate tank.

Have you asked the store where you purchased them if they would do a trade-in?

I would suspect that the warmer water temperatures are causing the fish to lay eggs. During spawning, the males chase the females relentlessly so that they can fertilize the eggs once she lays them. They can be pretty brutal about it, but it's normal and my fish do this everyday in the spring in the early morning. If yours do lay eggs, they will most likely be eaten right away since they won't be hidden in a plant.

I doubt they are fighting. Of the twenty-five fish in my pond, only one ever behaved in an aggressive way other than at spawning time. He would harass new fish I added to the pond for the first couple of days.

I do think the ten gallon tank is too small and agree with the suggestion that you put them in a child's pool or a plastic barrel pond if you have a garage or basement you could put them in.

Goldfish produce adhesive eggs that attach to aquatic vegetation. You have a perfect environment for breeding with having plants in the tank.

Goldfish are very hardy and adaptable to most environments, comets especially. They'll grow quickly in a larger tank or stay small if placed in something smaller.

The only problem with a small tank is - goldfish are considered one of the dirtiest fish. With the amount of waste they produce the ammonia levels rise quickly in the water.

During the winter I take them from the pond and put them in the wine barrel. I've had them for 8 years.

Hi Audrey,

You could put a partition between the fish, provided it allows water flow and aeration between the sections of the tank--I've done this with my cichlids--so they can't get to each other. I used suction cups to adhere to the sides of the aquarium and used plastic thread to attach them to a plastic mesh screen which I cut to fit tightly on the inside, and it worked great.

Kate (we've traded seeds)

Thanks, everybody, for your suggestions. The larger (possibly female) gold fish is probably about two inches, the smaller (aggressive one) more like an inch and a half.

It could be egg-laying behavior as suggested, since I think it usually is in the morning that the calico becomes more aggressive. Also the gold one does seem to miss him when he's gone, because she'll race back and forth in the tank for a while, as if she's looking for him.

Perhaps my bringing them in from the cooler temps outdoors made them think it was spring! I may try raising the light a little further above the aquarium--if I can figure out a way to do that--to keep the water cooler. Maybe I should cut the number of hours that I leave it on too.

I had considered getting a divider, but that would make the space available to each fish even smaller, so would probably stress them out more! Not to mention that I've already spent far too much money on these two.

I don't have room for another tank, and any larger container--like a barrel--would have to be kept in the basement. Which I'm afraid would be too dark.

Audrey, I didn't realize your fish are so small. The ten gallons should be fine for the winter, although next year they may grow enough to need something larger. They really don't need a light or any additional heat. Goldfish like cool temps and the light in the room is sufficient for them.

If you do put them in the basement for the winter once they are larger, they should be fine in low light and even the cold. The only time cold will kill them is if they are in a solidly frozen pond. Gases build up unless there is an opening in the ice for them to escape through. My fish stay out all winter with just a hole in the ice from a bubbler and I haven't lost a single one.

I was figuring on mating behavior myself too, but if they are doing that at 3 inches then they are stunted big time. Look on the gills, if one of the fishes has salt like specks on the gills it means its a breeding male.