What you're describing is more likely a response to the overcrowding of the tank. The rule of thumb for freshwater tanks is 1" of fish per gallon of water. You could probably get away with 3" worth of fish, but even if your goldfish are pretty small, you've got at least 5" worth of fish there (and probalby more). A tank of the size you describe is about right for a a single fish, or perhaps two. You could have 3 fish if they were the size of tetras. Reducing the number of fish in the tank should resolve the problem.

Your tank is inhumanely small for the number of fish you have. Goldfish need 10 gallons per fish, and as for "sucker-fish" what you're describing is a plectosomas, which should never be mixed with goldfish. They tend to eat the slimes coats on goldies which will eventually make them sick. Also, the plecto will grow to be about two feet long, so it is unsuited for the tank you have. "Survival of the fittest" describes competitive evolution over multiple generations, not competition in a 3 gallon bowl. In any case, goldfish eat mostly vegetable matter and are rarely antagonistic towards each other. You simply need a much larger tank for the number of fish you have.

I know my tank is too small for my fish, it's 5 gallons and I have two fish. They're doing fine for now because they're small... or maybe they're not. If anyone can answer my question as to why my spotted fantail goldfish is attacking my black moore, I would appreciate it. Since we got them about a week ago, they've been nudging each other here and there and I read that is normal; however, today, the spotted one seems to be very aggressive or territorial or something because he simply will not let it rest!! I feel awful for my black moore! help!!

A good rule of thumb is 2 gallons per inch of goldfish. A goldfish is a carp, in reality, and will grow to fit the tank. If you put them in a pond, they can get a couple feet long. If you want that color fish without the size, move away from goldfish to an orange or sunset platy. Goldfish also, contrary to popular belief, do not do as well in a bowl. They tend to foul it quickly, so need frequent water changes. Far better to put them in a larger tank with filtration. Some experts even suggest that a 55 gallon tank PER FISH is not too big. Also, be sure your tank is longer than it is high. A rule of thumb for that is that if your fish is longer than it is high, so should the tank be. If your fish is taller (i.e. silver dollars, angelfish, etc...) get a tank that is taller than it is wide.

WAY TO MANY FISH FOR THAT SMALL OF A TANK, GET YOURSELF A BIGGER TANK...lIKE MAYBE 10GAL!!

Because you have way to many fish in that tank. The rule of thumb of one or two inches per fish per gallon ONLY works for small tetra and the like. Once the fish get over three inches or so it is an entirely different matter. Goldfish are large (a foot long as adults), dirty (can produce 33% of their body weight in waste a day) and need no less than a thirty gallon tank for one. I would only have the set up you do in a 75 gallon tank. Though frankly, since I am answering this so long after you asked, they are already dead. It's a shame since both the goldfish and the plecostomus can all live 20 years with proper care.

So sorry, I was gone for so long. I went back to the pet store right away when this happened and they hemmed and hawed and finally admitted they sold me a melange of equipment that didn't go with the fish they sold me. I saved 3 of the 4 goldfish, bought a 30gal tank at a yard sale and gave the sucker-fish to a friend with a much larger tank. Oh, by the way, it's been 3 1/2 years and just so you know, all of the goldfish are thriving. / Oh, and brindle, you can lose that arrogant attitude. If I wanted to harm these fish I would never have asked. I'm a certified jeweller, not a fish expert.

your tank is the problem, you need a minimum of 10 gal per goldfish, with 20 gal per goldfish a better option. The tiny fish you buy in pet shops are only 3 to 4 month old babies, less than a quarter their full grown size. . Remember that goldfish are a very large and very long lived fish, each of yours will eventually grow between 8 to 12 inches in length, (and could get as big as 18 inches long, and I have heard of rare times when a goldfish has grown to 32" in length.... remember, goldfish are river carp, and river carp are simply HUGE!) and once full grown will require a 20 - 30 gal tank PER FISH. . There is a common misconception that you can keep a goldfish in a bowl, because it is a small and short lived fish. Nothing could be farther from the truth. Goldfish live as many as 50 years, though 10 to 30 years is a more common lifespan. And a full grown goldfish can be well over a foot long. . Keep in mind when buying your goldfish, that the tiny 2 - 3 inch fish in the pet store is a baby about 3 months old. By the time they are 3 years old, your fish will be at least 8 inches long. . Why do goldfish so often die less than 4 inches long and under 2 years old? Because by keeping them in a small bowl or tiny tank, they have no room to grow, their growth become stauned, and they die at a young age as a result. . I recommend you do several things: . First off, get another tank, 55 gal at least, 100 gal is better, for your four fish. Remember 4 times 20gal equals you need a tank 80gals, and also, get a SEPERATE 30 gal tank for you pleco (keeping in mind here that you pleco will grow to up to 40 inches long eventually, depending on what type of pleco it is... most are only 12 inches and thus need a 30 gal tank, the big ones will need as much as a 200 gal tank however. NEVER ever EVER keep plecos with Goldfish, they will eat your Goldfish. . Next, Put an overflow power filter on your tank IMMEDIATELY! Your fish is suffocating from lack of oxygen. . Third, add at least 1 airstone of no less than 4 inches long. . Check the PH level to be certain that it is between 7.2 to 7.6 as the wrong PH levels could be causing the problem as well. . Also test the ammonia and nitrate levels. If these are too high than they could be causing your fish to not get enough oxygen, even though you have a filter and airstone (bubbler). . The carbon in the filter should be replaced at least once a month, but some filters will require twice per month change. Also be sure to wash the filter sponge, using the old tank water (not tap water) to ensure that the "good bacteria" are not killed. (and if you are not using an over the top power filter, than you really should think about buying one, because this will greatly increase the oxygen level in your tank, and the carbon will help your fish as well.) . also, because goldfish are "messy" fish (meaning they produce a high rate of waste product in comparison to body size) it is imperative that you do a 1/4 to 1/3 water change each and every week, a 1/2 tank water change once per month, and a full tank cleaning (removal of fish to a mini-tank, while you completely remove all water, and hand wash the gravel, all filter parts, and plants, and decorations,) once every 6 to 8 months. Otherwise it would be the equivalent of you swimming in the city sewage system. . Remember, that goldfish are highly intelligent and social creatures. And like any intelligent creature, they will fight in crowded conditions. Just think of how you would feel if you had to share one twin sized bed with 6 brothers and sisters. That's how your fish are feeling right now, and if you was them, you'd be fighting too.

Why don't you keep them in a shot glass? They need a MUCH larger tank. I have 8 goldfish in a 100 gallon pond and they're running out of room. Then again one of mine is 13 inches long. ;) Don't mix suckers with them. You also might have diseases in there. Get some medication like tea tree oil and get that sucker out and get a bigger aquarium or just get a big plastic container till you can get a bigger aquarium and make sure you get either a bubler or a filter to introduce air into the water. Whatever you do NEVER put them in direct tap water. let it sit a few days before putting fish in tap water and if you can filter it or put a bubler in it for a few days prior even better.

You have to small of a tank. The rule for fish is 1 gallon per bigger fish [like goldfish and angelfish]and 1/2 gallon per smaller fish [like guppies, menows, tetras, bettas, and paties]. You need to get a bigger tank fast or your goldfish will die of lack of space and oxegen. I have 2 goldfish, 1 black moor goldfish, 3 yellow guppies, 2 shrimp, and 1 corrycat algae eater or sucker fish in my 15 gallon tank. So if given the space goldfish, algae eaters, and some tropical fish will get along.