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How to Choose Fish for a Freshwater Tank

I've had several community fish tanks, as well as tanks with fancy goldfish. I love how fish tanks add color and life to your home.

Get advice on choosing the right fish for your freshwater setup.

Get advice on choosing the right fish for your freshwater setup.

Starting a Freshwater Tank

It doesn't matter if you're new to the pet fish world or an old hat starting up a new tank: The biggest decision you need to make is which kind of fish to keep. Both fresh and saltwater tanks have lots of colorful, beautiful fish to choose from. For beginners, I suggest a freshwater tank since they deal with less chemistry and are easier to maintain. Because of that, this article focuses exclusively on freshwater tanks.

How to Choose Your Fish

If you choose to start a freshwater tank, the next important thing to think about is what fish you would like to keep in it. There are a number of successful groupings you may want to try, including community tanks, goldfish tanks, species-specific tanks, and cichlid tanks.

  • Community tanks have the advantage of being diverse, but you have to be careful to keep aggressive fish out of them as they can devastate a tank.
  • Goldfish tanks can be a bit more aggressive, but they really do best with their own kind, especially if they are fancy goldfish like Black Moores or Telescope Eyes.
  • Species-specific tanks are good for breeding fish like Guppies, or for schooling fish like Zebra Danios or Neon Tetras.
  • Cichlid tanks feature highly aggressive fish and should not be combined with the other types.

Setting Up the Tank

Goldfish and other fish that grow to large size usually need about 10 gallons of water per fish. Other fish typically need about one gallon per inch of fish. When you are choosing a tank and fish, it's good to keep those guidelines in mind so that you don't overstock your tank.

Cycling Your Tank

Also, it is necessary to allow a tank to "cycle" when it is first set up. I could cite a whole bunch of fancy speech at you about why it's needed, but all you really need to know is that your tank will take about a month to be safe for your favorite pet.

You can go about cycling in two ways:

  • One is to let the tank sit empty for a month.
  • The other is to buy a few inexpensive, hardy fish and allow them to adjust the water. Feeder goldfish and corydoras catfish are both good candidates for tank cycling. I have found that both are hardy enough to withstand cycling water and are inexpensive enough to be easily replaced.

Either way you do it, don't put your most prized, beautiful, exotic fish into the tank for at least a month after you set it up.

Remember to Include Bottom Feeders

Also, all tanks do better with some "bottom feeder" or "tank cleaner" fish. These fish (or invertebrates) keep tank and walls cleaner so that you have to change water/scrape out the tank less frequently. Good fish to buy to keep the tank clean include the following:

  • Corydoras catfish
  • Plecostomas
  • Apple snails
  • Chinese algae eaters

Warning: Plecos and Chinese Algae Eaters

A word of caution on the plecos and Chinese algae eaters: The plecos are delicate and easily die in poor water conditions. They also are very nocturnal, and it's not uncommon for them to hide all day. You should always provide a place for them to hide so that they feel safe during the day.

Chinese algae eaters can be very aggressive. I'd never seen that behavior until I kept one in my guppy tank two years back and it began shredding their fins. Later, I looked them up online and saw that they were, in fact, listed as semi-aggressive and did grow much larger than I originally believed. They should only be kept with other slightly aggressive fish and only in larger tanks.

PookPook: a healthy Black Moor Goldfish.

PookPook: a healthy Black Moor Goldfish.

Ensuring That Your Fish Are Friends, Not Enemies

The key to choosing fish is knowing how they will get along. There's nothing worse than watching your beloved fish chase each other to death. Here are some common fish and some recommended tank mates:

Common Goldfish

This is a semi-aggressive fish. They can be kept well with carp (read, catfish-like goldfish), other goldfish, and bottom feeders. Catfish and pleco's go just fine with common goldfish. I have heard of keeping Gourami's and other semi-aggressive fish with goldfish, though I have not tried it myself. Provided they are all about the same size that should work out just fine.

Celestial eye goldfish should only be kept with other fancy goldfish.

Celestial eye goldfish should only be kept with other fancy goldfish.

Fancy Goldfish

This includes fish such as the Black Moor and Telescope Eye goldfish. I really recommend that these fish be kept by themselves. I have seen a lot of fin and eye injuries in these fish if they are kept with anything but other fancy's and a few bottom feeders. Catfish and Pleco's seem to do okay with them, but anything fast or aggressive just tear up these fish unmercifully.

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Beta Fish

These aggressive fish can do well in much smaller tanks than most. They have a special organ that allows them to get oxygen from the air as well as the water. This means that a tank only holding a half gallon to a gallon of water would be acceptable for a lone beta. Many creative, fun types of small tanks are made for betas and can be bought for a reasonable price.

If you do purchase a small beta tank, I do recommend getting one with a filter so that cleaning can be less frequent. A snail in such a small tank is also a good idea because the beta will not harm it and the snail will help keep the tank clean. Also, betas can do well in a community tank with fast, small fish as long as they don't have any flowing fins to shred. Good tank mates include neon tetras and zebra danios.

Tetras, Barbs, Danios, and Other Schooling Fish

I do not include guppies or swordtails in this category because they are livebearers and slightly different. Good examples for this category include:

  • Zebra Danios
  • Bala Sharks
  • Ghost Glass Fish
  • Neon Tetras
  • Glowlight Tetras
  • Rosie Barbs
  • Red Eye Tetras

There are plenty of other Tetras and Barbs that fit here as well. These fish are very good to keep in a community tank and some can do okay with normal goldfish, though I don't recommend that they be kept with fancy goldfish since the fancies often have sight issues and long fins that can get torn up by fast little fish who can see better and swim faster.

Also, these fish do the best when kept in groups of five. At the very least groups of three are acceptable but their remarkable schooling behaviors are best observed when in larger groups. A few barbs can be mildly aggressive so try to keep them with fish of the same or larger size.

Loaches and Knife Fish

These fish are very dissimilar though their appearance is somewhat close. Loaches can come in a variety of shapes and sizes. Some are worm-like while others can resemble freshwater clownfish. They are generally passive, quiet fish that do well in a community tank. Knife Fish, by contrast, vary widely in their temperament. A few can be passive but most are extremely aggressive and will pretty much eat anything smaller than it in the tank. I've seen a friend's tank decimated by an aggressive knife fish.

Angels, Paradise Fish, and Gouramis

Angels and Gouramis are semi-aggressive fish that do alright in community tanks with other fish their own size. Some smaller, fast fish such as streamlined tetras or danios can do well with them also because they can move out of reach quickly. Paradise Fish are similar but they have flowing fins that can easily be damaged by fish of the same aggressiveness level. They can be kept with members of their own species and some bottom feeders.


I have less experience with cichlids and thus have less information on them. What I do know about them is that they are hyper aggressive and do not make good community tank members. They should only be kept in a strictly cichlid tank. However there is a large variety of them, so if you want a diverse tank you can still keep them just make sure that you keep them with others of the same type.

Guppies and Other Livebearers

I have had great success with guppies in a species specific tank. They breed like crazy in a slightly dirty tank. Give the babies a few places to hide and soon a three fish tank can turn into two-dozen fish tank. Fancy guppies come in dozens of colors and are quite beautiful to watch and raise.

Swordtails and some other livebearers can be hyper sensitive to water quality. If you are very careful to keep the water clean and at just the right temperature, these fish can be quite beautiful. They are fine to be kept in the same environment with the Tetras and Barbs.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.


fish guy on March 15, 2018:

i have a question i had put a lemon chilid small fish with goldfish in a 55 gallon tank and hes always chasing them so is he playing or fighting i also have plecos gouramis

Teresa0457 on July 30, 2014:

i have a five gallon tank with two corydoras catfish and two apple snails one fantail goldfish and a common goldfish.

Pieces on June 23, 2013:

hi! i would like to offer more information about african cichlids . here are the basics , 1. cichlids need a very large tank with a very large filter. 2. while most are aggressive not all are 3. if you over stock a tank with small cichlids ( young ones ) aggression tward tank mates is less likely , cichlids are territorial not aggressive they will deffend against anything or anyone this over stocking will result in the need for seperateing them out or upsizeing the tank later but it will be more harmonius in the long run , i have an 80 gal with 20 cichlids that will mostly all reach 7 inches or more. i will buy another tank some 10 years down the line and all will be fine 4. ciclids need a heater 5. there are well over 2000 cichlid species on the market most of them are beautiful and every last cichlid has a different personality 6. they need hard water

for more information on cichlids check out my blog at

please comment or ask questions there , they will be answered ! thank you

fabien roets on May 08, 2013:

hey got a black moor goldfish. how can i tell him/her apart ....... its under 1 year old......

jonno96 from Australia on December 07, 2012:


jonno96 from Australia on December 07, 2012:


Laura on November 04, 2012:


We have a 50 gallon tank. In our tank we have one kissie fish, one tiger fish, two angel fish, one albino shark, two red tailed shark, two tetra fish, one bottom fish which he is getting big, two male betas, which they get along well. We introduce them first together in the huge tank which we were told we could not do but they are getting along well like brothers. Just information to let you know. Also in our tank we have a big log with big holes in it with plastic plants on it which the sharks like to be in it.

octaviaslady (author) from South Carolina on July 04, 2012:

That's a good question. My experience with goldfish is that they are extremely hardy and are rarely harmed by warmer water. Right now my husband has 2 fantails in a sand-bottom aquarium with two corydoras catfish and a plecostomas and they're doing fine. I have had the same combination with a gravel bottom no problem. I do know experts say goldfish do best in cold water and I am sure it is true. All I can tell you is my personal experience is that the goldfish are usually the hardiest ones in the tank (aside from the special concerns of fancies such as nipped fins/bulging eyes etc) and if you set up conditions for the other species in the tank they seem to do very well with them.

chicke351 on July 04, 2012:

I have a tank which is aprox. 300 litres. I currently have two fantails in it because one of my fantails killed 5 of my other fantails by nipping their find, and unfortunately none recovered. I just a week ago introduced the second fantail and everything is fine. I'm wondering what breeds of bottom feeders are suitable with them?? All bottom feeders a find info on either require sand (I have gravel) or warmer temperatures, and I don't want to warm the water up as my babies thrive in the cold water. :)

Luke on April 04, 2012:

To first comment holder

bad idea to mix goldfish and barbs

other than that you should be right

I have comets Shubunkins and fancies in 1 100 G tank and going well

Nixxx on February 28, 2012:

Sorry for the typos, my smartphone isn't so smart with it's snooty autocorrect.


Nixxx on February 28, 2012:

Hey there!

Great site, thank you for all the great info. Now I need some advice. For Christmas I got my son a small 5 gal tank for the Glofish he wanted, but, the attendant at petco told me my tank had to cycle for a month before I could put the Glofish in. I asked what I could take home that day to give my son some immediate gratification and she suggested goldfish. So, he picked out two beautiful Shubunkins that are doing great. A month later, er went back and purchased three Glofish. I asked the attendant if the shubunkins were compatible with the Glofish asks she said yes. One died the very next day. I figured the fish didn't acclimate as well as the others. We went back to replace it but my sin decided he liked the neon tetra's. Again, I asked about compatibility with the other fish currently in the tank she was assured that they would all peacefully coexist. So, here we are about a week in after getting the tetra's and I've noticed that one is constantly hiding, I've had to move the coral/cave/plant decoration that was in there to see if he was possibly dead, but he wasn't, he was just hiding. The other tetra had been lazily drifting and kept getting caught against the back of the filter and the tank wall. I freed him several times buy knew he probably wouldn't make it much longer, and I was right, I just found him belly up. The other tetra came out during the commotion of me removing his departed buddy, but quickly went back into hiding. I'm assuming that the tetra is stressed out, but I'm not sure what out could be from. I realize now that they would do much better in groups of five or more but don't want to overcrowd the small tank. One tetra that's already stressed probably doesn't stand much of a chance now though, right? I know that when the shubunkins get a little bigger they'll need a bigger tank, but for now they, and the Glofish, seem fine. 2 shubunkins, 2 Glofish, and one tetra...should I get another few tetras, Glofish, or leave them as they are? I feel bad for the lone tetra but am worried that if I get more tetras the current one will die and that the two or three new ones will start to feel stressed all over again.

I duo know that I definitely need a larger tank, and soon, but this was just spudded to be an introduction tank for my son (and myself obviously). Any archive would be helpful., I've found myself attached to these fish and fond their presence relaxing, I love watching the bright colors and gracefulness of their swimming but don't want to see them hurt or stressed.



dreamer on February 19, 2012:

Hii, M a newbie in the aquarium world

I have 2 angelfish, 2 tiger sharks(as the shop keeper says) and one catfish in my 40 gallon tank.

i got a prblm wid shark, on my sharks body i saw blood like thread and its lay on my tank bottom..

is it ill?..

my all fishes are all right except sharks

or anything else plzzz Help me.

wht to do?

Cody on February 17, 2012:

Hello, I have a 75 Gallon fish tank currently with goldfish in it. I have 3 Gold Carp, the largest being about 5.5 inches long and the smallest being about 4 inches. 1 large black moor, 1 Pearlscale, 1 Redcap, and 2 Fancy Goldfish. I also have a medium size Plecostomus and 2 snails. I would like to get something different for the tank, and I was wondering what would work well with the large carp? Would Cichlids pick on a fish thats 5.5 to 6 inches long? Currently the fish in the tank now get along just fine, I was just curious about how cichlids would get along with carp.

octaviaslady (author) from South Carolina on February 12, 2012:

Hello jjmw,

The Oranda wouldn't get lonely, but I think the 2 gallon starter is probably a bit small. Go with at least a 5 to 10 gallon. The only fish I would put in less than a 5 gallon is a beta fish.

jjmw on February 12, 2012:

I am thinking about getting a Oranda goldfish, and I was wondering if a 1.77 gallon starter goldfish kit would be big enough. I was also wondering if it was ok that the Orada goldfish lived by itself?

Jyotiraditya on January 21, 2012:

hey..can I keeg gouramies & angels with the carps..?

InterestCaptured on January 11, 2012:

goldfish are coldwater fish and should not be kept with tropicals, in addition to having different requirements, goldfish create too much waste too fast to be kept with tropicals

CZCZCZ from Oregon on January 03, 2012:

I enjoy my Cichlid tank they are fun to watch swimming around the rocks and caves that have been set up in the aquarium. I have an all malawi tank to keeo it simple so not a community tank in some regards but there is a few different species in there.

octaviaslady (author) from South Carolina on December 07, 2011:

Hello Monnkin,

The short answer is yes. I think you could get away with it just fine at least until your fish gets really big. Good luck and enjoy your black moor!

TheHappyMonnkin on December 05, 2011:


you seem to be very helpful when it comes to fish... so i why not, and ask you a question. My roommates just recently bought me a 10 gallon tank and filter for Christmas. Ive always had my heart set on a black moor since i started getting into fish a few years ago. I was just wondering if it would be ok to squeak by with my new ten gallon tank. I have two ottos currently, and a male Betta. However if i do end up getting a moor Im just going to leave the betta in his current 5 gal tank. :') i've read that the two don't get a long. But again, I guess my question is, would it be possible for me to get a black moor goldfish and keep him in a 10 gallon tank with two algae eaters?

thank you!

octaviaslady (author) from South Carolina on November 27, 2011:

Hello Merina,

As they get larger, the angel fish will most likely become aggressive. You may get away with the fantail goldfish because the angels are the slowest of the cichlid family. However, this limits you in what can get along with your tank community. You will definitely want some clean-up fish such as corydoras cat fish and a plecostomas or apple snail. The larger the tank the more bottom feeders and algae eaters you will need. If you are looking for a few more fast, flashy fish, I recommend neon tetras, platys, guppies or mollies. All of these small fish are fast, school well for a pretty effect, have nice colors and are tame enough not to bother your fantails too much. They also run a risk of becoming bullied by your angelfish, but their superior speed should keep them safe for the most part. One note about them, however. As they are schooling fish they do better in groups of three or more, so I would pick one type and load up on four or five of them. It is delightful to watch them school through your plants and rocks!

Good luck!

merina on November 26, 2011:

hello i just went thrgh the site, i got 2 fantailed goldfish & 2 angelfish,will there be any problem,they are small.its my 1st fish tank.which more can fish i can introduce into my new tank??

Newbie on September 18, 2011:

thank you octaviaslady, very much appreciated. Godbless!

octaviaslady (author) from South Carolina on September 17, 2011:

Hello Newbie,

Congratulations on starting a new tank. Riyukin goldfish are very pretty and I'm sure they will look lovely in your tank once it is established.

Cycling will occur no matter what you do. Since you put fish into your tank right away, some of them may get sick or die because the water's ph, etc has not had a chance to settle. However, once the first two months or so is over with your tank population should be more permanent.

As for the threads on the tails it may be a parasite such as Gyrodactylus. It may also be an elevated level of ammonia in the water. Gold fish are very dirty fish. Since you have completely filled your tank with them, I recommend you try changing out half of the water today and the other half tomorrow or the next day. You can buy kits to test water ammonia but it's always good to keep the water as fresh as possible. If that doesn't work, try some parasite guard to get rid of any parasites. Good luck!

Newbie on September 17, 2011:

Hello, i would like to ask you. i am new in this aquarium/fish keeping, i bought 6 riyukin gf for my 58 gallon fish tank last two weeks or so, can i still continue with "cycling" i am a newbie, can you instruct me what to do? i think my gf's are sick, they have bloodlike threads on their tails

octaviaslady (author) from South Carolina on September 16, 2011:

Hello Billy,

Well, I think the black moor and oranda situation sounds just fine. The red caps may gang up on the black moor (they can see better than he can), so I might get a slightly larger black moor just to be safe. As far as the bala sharks and pangasius, I think the 20 gallon may not be large enough for them forever. Pangasius can get up to 3 feet long and bala sharks are no slouch either. For a while they would be fine with a plecostomus (also a big grower and fun to watch), some very fast tetras or even a gourami or two. Watch out for gouramis, though, they can be mean if you aren't careful so make sure to match the size of any you get with the size of your current fish. Always make sure the gourami is the same size or smaller than the fish you already have.

Hope that helps and enjoy!

Billy on September 16, 2011:

i have two orandas, two bala shark and two Pangasius catfish in a 40 Gallon tank. I am planning to move my bala sharks and Pangasius Catfish in my 20 Gallon tank. that leaves my two orandas in my 40G tank, can put 1 black moor and 1 Red Cap Orandas, would that be enough? what tankmates can you suggest for my 20G tank with bala shark and P.Catfish?

carolinemoon on September 13, 2011:

I love those cute little ones with big eyes. They're unique!

Daisy on September 02, 2011:

ok thank u so much for ur advice

octaviaslady (author) from South Carolina on September 02, 2011:

Hello Daisy,

The ten gallon tank should be enough for now. They may grow too large for it eventually but right now they should be fine. As for the white fuzzy stuff there are several options. It could be ick or it could be any other number of bacterial infections. Ick medication or methyl blue may work for him. Go to an upscale pet store. Take a picture of your fish on your phone to show the employees. They should be able to give you the right medication. It may or may not be too late for him but at least that will give him a fighting chance. Good luck!

daisy on September 02, 2011:

HI, i have 1 black moor and 1 redcap goldfish and they are in a 10 gallon tank... is 10 gallons enough? and i have only had them for about three weeks and they are very close in size but the redcap is just sitting at the bottem with white fuzzy like stuff all over it. i tested the water and everything is normal but is just sitting at the bottom and when i feed it it eats but when its done goes right back to the bottom... what is it doing is it going to die?

octaviaslady (author) from South Carolina on August 10, 2011:

daze1dog: Betta fish are very aggressive to any fish with flowing fins. It will most likely kill your fantails.

daze1dog on August 10, 2011:

can i put a batta in with my gold fish they are fantails

Patricia Dominice from Atlanta, GA on April 16, 2011:

Nice article! Very informative...I love keeping tanks as well!

Lauren on February 16, 2011:

Hi there,

I recently bought a black moor goldfish, and rather foolishly assumed that it could be kept in a regular fish bowl. After reading a few articles, I've found that this will be a problem as it grows... and I hope to remedy the situation. Would a 2.5 gallon tank be alright, or do I need to find something even bigger than that? I currently have a 10 gallon community tank, with a blue dwarf gourami and five guppies - but after reading the earlier comments, I don't plan to house the black moor with them.

Also, would a female betta and male gourami be alright if kept in the same tank?

octaviaslady (author) from South Carolina on January 12, 2011:

Karly- I would let the new guy mature in the 16 gallon before letting him in with the Orandas. It's just good policy to keep your fish about the same size. Now he doesn't have to be EXACTLY the same size when you introduce him, but at least get him over half the size of the other two.

Meg- I have heard that some free swimming cat fish such as the pictus can work well in a semi-aggressive tank. They like to school, are in constant motion and get to be around six inches long. So that's my suggestion!

aquarium hero from malaysia on January 07, 2011:

what a nice clean neat tank you have! nice info about choosing fish, yeah compatible fish are really important. thanks!

Meg on November 16, 2010:

I recently set up an awesome 55 gallon tank I am doing semi-aggresive fish I have 8 tiger barbs,3 gold gouramis and 2 blue ones I also have three bala sharks which I know are going to get big and I am prepared for that does anybody have any other suggestions on any other kinds I have heard clown loaches do well but what else..?

Kevlin on October 22, 2010:


Very Nice Your Article

Hits $$$$ f u Success

Karly on September 27, 2010:


I have a couple questions about my fish. I have two beautiful Orandas who are both about 5-5.5 inches long. One is more wide and tall than the other but, lengthwise, they're the same. My tank is only 16 gallons. (I know, this isn't good for them and I am trying to remedy the situation ASAP!)

Basically, I'm wondering how big of a tank I should get. 30, 40, 60 gallons?

And, I really want a ranchu. I finally found a local store that carries them but they've only got tiny babies (about 1.5 inches long). Were I to get one, would it be more wise to put it in the 16 gallon tank until it got bigger or will it be okay if it has enough places to hide with my two Orandas in the new tank? I'm planning on planting my new bigger tank with live plants.

amy on September 22, 2010:

I've had my fancy goldfish for about 9 years. THere is four left and all they do is lay on the bottom of the tank. When it comes feeding time they get up for that? But not to swim around? I've tried everything from water changes to ph...still no luck. I feel really bad for them. This isn't the quality of life I would like them to have..what should I do?

jencloey on September 06, 2010:

I should add that the first goldfish was a gold common goldfish. As I said before, it was about 2 years old and maybe 2 inches long. It was the 2nd largest fish in the tank at that time. The second goldfish was a black moore that is about 1 year old and is also about 2 inches long. The first goldfish killed off other, smaller goldfish and the black moore killed off various fish that were also about 1 year old as well, and they had been the same fish in the tank for the entire year (as was with the first goldfish).

jencloey on September 06, 2010:

Hi All! I have a question/concern regarding goldfish with other community fish. I have had two experiences with goldfish that were fine with other fish until they reached a certain size (about 1 1/2 - 2 inches). At first, I thought a fish had died and they were pecking at it. However, later on, I seen a goldfish peck another fish to death. That fish was about 2 years old and I got rid of it after it destroyed about 5 other fish. A few years later, I had another goldfish that after about 1 year of having it, it starting killing off the other fish. Is this common for goldfish once they get too big to be small (15 gallon) fishtank fish, or is it once they have started pecking at fish, it becomes a habit. I want to get new fish for my tank, but I am wondering if I should just avoid goldfish all together and isoloate my remaining "killer" goldfish.

octaviaslady (author) from South Carolina on July 09, 2010:

Hello Dee,

Thanks for the comment. The thing about fantails is that they can see much better than black moors. Because of that advantage, the fantail is much more likely to beat up on the black moor. Not much you can do about it except give the black moors plenty of areas to hide, like under rocks or fake logs. Other wise, get another tank for your black moors.

Dee on July 08, 2010:


My sister recently bought my niece a fish tank and it now holds two small black moors and a fantail. I was wondering if it was usual for the fantail to chase the black moors. one of the black moors is slightly larger and the other slightly smaller than the fantail but the fantail doesn't seem to discriminate in its trouble making and chase's them both around the tank until they are in the corners or well away from it.

octaviaslady (author) from South Carolina on July 01, 2010:

mariL- the simple answer is no. I have seen both angel fish and tiger barbs get very aggressive and the telescope eye goldfish would get beaten up or killed sooner or later. Even if they're okay at first, the angel fish will grow much faster than anything else in the tank and will end up huge, mean and deadly to the other fish.

mariL on July 01, 2010:

Hi, could you give me advise, if I can have tiger barbs, telescope eye goldfishes and angelfishes tin the same tank? on June 12, 2010:

The ph is about 6.8 and water is about 65. I think you have it. This surviving fish (is almost 4 1/2 inches) and is double the size of all the other fish. Again thanks for you immediate respond and probably correct solution.

octaviaslady (author) from South Carolina on June 11, 2010:

Hello dordonia,

Are you sure your one fish got violent or could water ph or quality be the culprit? Sometimes fish will get aggressive as they get larger, but this many at once is a little rare. Especially since you have all the same kind of fish in the tank. Did this fish get a lot bigger than the others? If so, you might be save getting some more fish around the same size it is now. If not, check your water quality before you reintroduce any more fish. Also, no matter what other fish you put in a tank, having a bottom feeder like a cat fish and an algae eater like a plecostomus are always a good idea. on June 11, 2010:

I have a 55 gallon tank which I thought would be a great home for low maintenance goldfish. I bought 11 feeder goldfish and for 4 months every was great. They all started growing and no fighting. I only had to clean algae and change water. Last week, two fish died and I did the regular water change and cleaning. The last two days now all are dead except one and he is eating the remaining dead one. Is this common for a fish to be so dominate and kill all the fish in the tank.

Thanks, I have never seen anything like this.

red squirrel on February 23, 2010:

Thanks for the advice. While it was too late for the oranda in question (the stress must have done for it), I recognised aggressive behaviour from one of the shubunkins. I isolated it for 2 days and it has been peaceful since it's re-introduction to the tank. I'll act sooner if the little monster plays up again!

Rany on February 20, 2010:

I just got a new aquarium nad i got 2 Gold fish,2 bala sharks, 2 tetras,and a pictus catfish,and i went in the room earlier and the goldfish has a strane of his fin offshould i put them in there own tank and will the goldfish be ok?

lainau on February 20, 2010:

? i have a red slider turtle 2 gold fish & a fancy tail goldfish in the same tank right now for bout a yr i am looking to get a bigger tank & possibly put in some tropical fish..since the water is kept warm already for my turtle..would that be ok? what kind of water should i put in i have well water & they do good but i get alot of alge sowould a alge eater be ok with them also? my turtle is still small...

octaviaslady (author) from South Carolina on February 18, 2010:

This is all the evidence of bullying your tank needs. Someone has decided that they don't like your oranda and is chasing them into the corner. I've seen this behavior many times and the aggression can seem subtle at first, but it will soon become obvious who is intimidating your fish.

red squirrel on February 17, 2010:

I have inherited a 3ft long by 1 ft deep by 18inch high tank. Tank has been matured and populated by the same fish for 3 months. I have 3 red goldfish, 3 lemon goldfish, 4 shubunkins and 2 red cap orandas, all small/small-ish. Water & filter changes made as per script, feeding and lighting regimens adhered to and chlorine levels monitored but one oranda has suddenly developed what seem like semi-shredded tail fins. Tank seems peaceful with no evidence of "bullying" but the oranda has taken to sheltering in a quiet corner, is this a sign of spawning or something more?

Silver Poet from the computer of a midwestern American writer on February 16, 2010:

Great informative hub. I like aquarium fish, and you're quite right: goldfish get aggressive sometimes. (To the folks about who want to mix bettas with other fish, I have successfully mixed female bettas with other peaceful fish, and they do well.)

octaviaslady (author) from South Carolina on February 12, 2010:

My husband tried that exact combination and the beta tore up the black moor really badly the first night they were together. I wouldn't try it if you value your goldfish.

Monica on February 11, 2010:

ok i have around 10 guppies and one male batta fish

with a peppered catfish and they are all doing fine

but I'm putting them in a bigger tank a 20 gallon and

i was wondering if the male batta would fight with the

black moor goldfish because the betta fight with brightly

colored long tail fish but maybe the black moor will be ok? I have 3 other spare tanks so if they don't get along i can move the batta fish but have people had any success keeping them together?

octaviaslady (author) from South Carolina on February 01, 2010:

Telling the difference between female and male guppies can be a challenge. Females are larger and have plainer colors than the males. In fancy guppies, males have huge pluming tails and fins while the females simply have smaller, colorful fins. I have not raised any other kind of guppy so I'm not sure if it is easier or harder to tell with them. I'm glad your goldfish gets along with them. Some do, some don't. A lot of it has to do with individual fish personalities!

Unknown123623 on January 31, 2010:

My guppies and one of my new goldfish get along even with guppy babies! And um.. can you tell the difference between male and female guppies?

octaviaslady (author) from South Carolina on December 24, 2009:

Well you have a few options. The best one is to get a bigger tank if you are going to have a lot of goldfish. If that is not an option for you, either for financial or space reasons, there are a few ways to at least make things more livable for your fish. #1 is to change the water frequently with same-temperature anti-chlorinated water (there are additives you can use or simply let your water stand out for 24 hours). There are also some products that will neutralize some ammonia, but I have not used them personally. The only way to completely fix the problem, though, is to follow the rule of the inch- one inch of fish per gallon of water. As the fish grow, the tank has to, too.

I hope that helps!

Neko on December 23, 2009:

Help me please! i have a 10 galon tank and a comet goldfisha nd common goldfish in my tank. Is that good enough space? they seen to be fine and i just got 3 more goldfish what should i do to keep amonia down and fish safe?

octaviaslady (author) from South Carolina on December 14, 2009:

My suggestion would be to put the goldfish in the 30 gallon community tank. yes, tetras may nip the fins of a large oranda, but mollies and guppies are rather tame fish and most likely will be fine with the goldfish. It is much preferable to have him in there with them than with the puffers. I think that would be the best choice.

xomelis on December 14, 2009:

i have a 30 gallon tank that contains some guppies, tetras and mollies