Semi-Aggressive Freshwater Fish for a Tropical Aquarium

Updated on October 31, 2017
EricDockett profile image

Eric is an aquarium enthusiast with over two decades of experience caring for a wide array of tropical fish.

Semi-aggressive freshwater fish can get along in your tropical aquarium, as long as you understand their needs and limitations.
Semi-aggressive freshwater fish can get along in your tropical aquarium, as long as you understand their needs and limitations. | Source

What Makes a Fish Semi-Aggressive?

You may have seen tropical fish labeled as semi-aggressive and wondered if they were smart choices for your freshwater aquarium. This label can be confusing, and not all fish earn it for the same reason.

What does semi-aggressive fish mean? It sounds like these fish are violent, but only part of the time. Like, maybe every now and then they just go berserk, but most of time they are calm and peaceful.

Well, not exactly. When a fish is labeled semi-aggressive it usually means, under the right circumstances, the fish can be very aggressive. Very aggressive means it could attack other fish and kill them, eat other fish as food, or relentlessly chase other fish around until they die of stress.

On the other hand, under the right circumstances, a semi-aggressive fish can be very docile. While we can never know exactly what a fish is going to do, we can predict with a fair amount of success how they’ll react in different situations due to their temperament and natural habits. This means, if we stock our tanks wisely, even a semi-aggressive species can be a very peaceful community fish.

The first step is to know the fish you plan to stock in your aquarium. In this article we’ll take a look at many common semi-aggressive tropical fish and what makes them potentially dangerous to other inhabitants of your tank. If you understand these fish before you stock them, you can make sure everybody gets along, and reduce the chances of aggression in your aquarium.

The gourami is considered a semi-aggressive fish species.
The gourami is considered a semi-aggressive fish species. | Source

Territorial Fish

Some fish just don’t like other fish in their space, and because of this they get the label of “semi-aggressive”. In reality, it you match them up with the right tank mates, the instances of conflict can be greatly reduced.

  • Angelfish: Freshwater angelfish are new-world cichlids, and cichlids tend to be aggressive fish. They may or may not get along well with others of their kind, and they may be somewhat aggressive toward small, active fish. Consider medium-sized semi-aggressive tank mates such as gouramis, and slightly larger schooling fish like black-skirt tetras. Don’t overstock the tank, and make sure the water conditions are pristine.
  • Gouramis: If you decide to keep gouramis make sure you have plenty of hiding spots in your tank in case one decides to pick on the other. Sometimes they may get along fabulously, and other times the dominant fish may decide it doesn’t want the other anywhere near it. As you can imagine, this is extremely stressful for the weaker fish, and can even lead to death. Less frequently, and especially if the tank is overcrowded, gouramis may torment other fish species as well.

Beautiful Adult Angelfish

  • Plecostomus: You’ll often see plecos labeled as semi-aggressive. These are the sucker fish who stick to the side of the tank. How mean can they be? Usually not very, but when their needs aren’t fully met they can get aggressive, especially when there is food in the water. Plecos need plenty of algae wafers as a supplement to the tank algae they’ll eat, and it’s a good idea to have a piece of driftwood in the aquarium. If you are meeting the nutritional needs of your pleco you should have no problems. If not, you may see him lashing out at other fish during feeding time.
  • Rainbow Shark: Aka, red-tail shark. These guys are wonderful fish, but they can get tough in certain circumstances. First, be wary of having more than one per tank, as they may not tolerate each other. You’ll also want to avoid other fish that look similar, such as bala sharks (more on them later). Finally, you never want your rainbow shark to be the bully on the block. It’s best to house him wither other semi-aggressive species, his size or larger, that he can’t push around.

Discus are another species of new-world cichlid that may be aggressive, and they grow large enough to eat smaller fish.
Discus are another species of new-world cichlid that may be aggressive, and they grow large enough to eat smaller fish. | Source

Big Fish

Big fish eat little fish. That’s the bottom line! Because of their big mouths and big appetites some otherwise docile fish get labeled as “semi-aggressive”. Really, they’re just looking for lunch.

As the fishkeeper it’s your responsibility to make sure the little guys are safe from the big guys. This means picking fish that will cohabitate in your tank, rather than establishing a mini food chain.

A good example:

  • Leopard Bush Fish: Also known as Spotted Climbing Perch, Leopard Gourami and African Leaf Fish. This is a very peaceful fish, and one of my personal favorites. However, it’s also highly predatory, and will eat anything that will fit in its mouth. It should not be kept with aggressive species, as its peaceful nature makes it an easy target. However, it may exhibit aggressive behaviors toward other anabantids, such as gouramis. Best tank mates are any peaceful fish that are large enough that it can’t eat them!

Other fish that may be dangerous for anything that will fit in their mouth include bala sharks, red-tail barbs and silver dollars. They are generally peaceful shoaling fish, but if they can eat a smaller fish they will.

If you have such large fish in your tank, you want to stay away from small fish species such as neons and other small tetras, guppies, otos, ghost shrimp and small danios. Unless, of course, you are serving up an expensive dinner.

Bala sharks are semi-aggressive fish that grow over a foot long.
Bala sharks are semi-aggressive fish that grow over a foot long. | Source

Semi-aggressive Schooling Fish

Some schooling (shoaling) fish are very active, and because they need to be in large groups they tend to get a little anxious in tank settings. Even little neons can get nippy at each other when tank conditions aren’t right. Of course neons aren’t considered semi-aggressive because they really can’t do much harm to other fish in the tank, but if they were bigger it may be a different story.

Large, fast-moving fish such as bala sharks, tiger barbs and tinfoil barbs, and even littler fish like cherry barbs, can cause chaos if the tank is too small and they don’t have the appropriate number of fish in their shoal. They may chase each other relentlessly, and may even pick on other species, particularly if they are smaller.

Whenever you see shoaling fish that are labeled “semi-aggressive” this is usually why. This behavior isn’t territorial or really “aggressive” at all, but instead a stress reaction to unsuitable conditions. The solution is to keep these fish in groups of at least six, preferably more, and in large enough tanks.

As you can imagine, for fish like bala sharks and tinfoil barbs that can grow beyond twelve inches in length you will need a very large tank. For the average aquarium owner (even those with 55-gallon setups) these fish are way too large, and it’s unrealistic to expect to keep them without problems.

African cichlids are beautiful fish, but can be highly aggressive.
African cichlids are beautiful fish, but can be highly aggressive. | Source

African Cichlids

Most African cichlids are highly territorial and very aggressive. They should not be kept with other tropical fish species, even new-world cichlids such as angelfish or discus fish. A cichlid tank requires a great deal of research before you go out and purchase fish, and you need to know just how to set up the aquarium.

The environments of the great African rift lakes, where these cichlids come from, is vastly different than the tropical lakes and rivers most other aquarium fish live in. African cichlids are just a totally different kind of fish, and you have to know what you are doing to keep them successfully.

That said, cichlid tanks can be very beautiful and highly rewarding. They’re about as close as you can get to the vibrant colors of saltwater fish without the expense and hassle of maintaining a marine setup.

If you want to go the cichlid route, take the time to learn about them and understand which fish can and should be kept together. Realize that you’re going to need a large tank (55-gallon minimum) and you’ll need to provide a lot of places for your fish to hide.

African cichlids are beautiful and rewarding fish, but can be a nightmare for aquarium owners who aren't aware of what they are getting themselves into.

Betta fish may do okay in a community tank, but usually they are better off living alone.
Betta fish may do okay in a community tank, but usually they are better off living alone. | Source

Single-Specimen Tanks

Some fish are simply too aggressive to be kept with other fish. This may be because they are territorial, or it may be because of their appetite. Or, sometimes it’s a combination of both. Here are a few fish you may want to keep alone.

  • Oscar: These guys are big, aggressive and will eat up any smaller fish they can. In very big tanks oscars can have tankmates, under certain conditions. Other large cichlids are a good choice, and other oscars. But even in the best of circumstances your oscar may not tolerate anything else in its tank. Very often, oscars are best kept in single-specimen tanks.
  • Green Spotted Puffer: If you bought of these fish because it was labeled as a semi-aggressive freshwater fish you aren’t the first to be duped. In reality, green spotted puffer care can be very challenging, These are highly aggressive fish that need to live in brackish water, usually by themselves. Sometimes puffers do okay in very large tanks with other puffers, but generally you’re better off keeping your green spotter puffer alone. Puffers have special needs, and if you plan to keep one make sure you research proper green spotted puffer care.
  • Betta Fish: Male bettas can live in community aquariums under certain conditions, but to save yourself and the betta a great deal of stress you’re usually better off keeping him alone. Bettas have a reputation as dangerous fish, but that’s not really accurate. Yes, they will fight each other to the death, but their reaction to other fish may be aggressive, or completely indifferent. If you want to keep your betta with other fish make sure you understand what’s involved in keeping a Betta in a community tank. Otherwise, he should live by himself.

Keeping Your Semi-Aggressive Population Happy

If you want to keep fish that are considered semi-aggressive in your tropical aquarium you need to understand the potential issues. Always do your research, and find out why a certain fish can be aggressive at times. Make sure you stock your tank in a way that alleviates most of the issues.

You can never keep a fish tank totally stress-free, but by making smart choices you can keep aggression to a minimum. Good luck!

Still Thinking About Adding Semi-Aggressive Fish to Your Tank?

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    • EricDockett profile imageAUTHOR

      Eric Dockett 

      11 months ago from USA

      Hi Anthony. That's tough to answer without knowing what fish you intend to stock in the "aggressive" tank.

    • profile image

      Anthony Rosas 

      11 months ago

      I have a non-aggressive tank and I am getting an aggressive tank soon. Would semi-aggressive fish be better off in the aggressive tank or the non-aggressive tank or maybe a tank of their own idk what to do?

    • EricDockett profile imageAUTHOR

      Eric Dockett 

      22 months ago from USA

      @Fahmida: I'm so sorry to hear about this disaster. You do seem to have an odd mix of fish there, and some that get a little large. You said your tank wasn't big enough for the blood parrot - do you think it might be over-crowded and this may have led to the aggression?

      I hope your situation improves and I'm sorry about the loss of your favorite fish.

    • profile image

      Fahmida Mily 

      22 months ago

      I bought a pair of blood parrot yesterday.I had dollar,albino,comet and small pearl scale fishes in my tank for a long time. As my tank is not large enough for parrots, I made a hiding place for them as this fish is a little bit shy. I am thinking of buying a large tank soon. But few hours ago I went to check on the fishes and I could not believe what I saw. One of my pearl scale was floating on the water lifelessly.The parrot ate it's head and tail.The another pearl was almost dead.Those pearl scale was my favourite ones.I'm heart broken now.I never heard of parrot eating pearl scale before. They r aggressive to my other fishes too.Always trying to attack them.

    • EricDockett profile imageAUTHOR

      Eric Dockett 

      2 years ago from USA

      Hi Hailey! You can try it, but you never know now the Betta will react to the ghost shrimp (even the female). They may ignore the shrimp, or they may chase and harass them. Have a backup plan in place (like the old tank) in case things don't work out. Good luck!

    • profile image


      2 years ago

      I have three bettas each in their own tank (two five gallons and one ten). One is a female and two are males, I was wondering if it would be better to move the female to my newest tank that only has ghost shrimp or one of the males. The female and one of my males are not too aggressive, but I wasn't sure.

    • EricDockett profile imageAUTHOR

      Eric Dockett 

      2 years ago from USA

      Bill, I'm not sure if you are joking or not, but it sounds like your tank is a ticking bomb. It's only a matter of time before disaster happens. Are they juveniles? I strongly suggest separating the male Bettas.

    • profile image


      2 years ago

      I keep 6 bettaz in a community tank. They are all brothers nd sisters. 4 males 2 females. Now and then they flare at each other, the rest of the time they get along fine.

    • EricDockett profile imageAUTHOR

      Eric Dockett 

      3 years ago from USA

      Wow! Sounds awesome, Craig. That must be a huge tank!

    • profile image

      Craig Martin 

      3 years ago

      I have a very unique, "semi-aggressive" tank. It's been up and running now for over a year and everyone gets along fine. 2 Clown loaches, 2 Angelicus botia, a pleco, 2chinese algae eaters, 4 corries, 1 upsidedown catfish, 5red minor tetras, 5 black skirt tetras, 5 black neons, 1 rainbow shark, 2 balas, 3 silver dollars, 3 angelfish, 3 Australian rainbowfish, 1 African leaf fish, 2 blue ram cichlids...don't think I left anybody out... very entertaining tank with very low stress! kinda happened by accident

    • profile image


      3 years ago

      Never had a Betta I couldn't keep in a community tank, but the trick is choosing fish the Betta won't see as a threat or competition. On the other hand, you don't want to keep anything that will be tempted to snack on those long fins either. A planted 10gal with a single male betta, 5 neon tetras and an otto or two would be a perfect setup

    • profile image


      4 years ago

      I will be getting a betta fish thanks to this hubs info. If you are going to be geeting a fish you should read some of this information. Yes, how big and what kind of tank I'm supposed to get. Thanks

      I rate this hub a thumbs up

    • pinappu profile image


      4 years ago from India

      I love those fishes. Betta is a gorgeous looking fish but it is aggressive (alas!).

    • EricDockett profile imageAUTHOR

      Eric Dockett 

      5 years ago from USA

      Hi Donny. My experience with redtails is it's best to only have one. They are fast moving and aggressive to smaller fish, and even some bigger ones, so it's smart to stock your tank with semi-aggressive fish that can hold their own.

    • profile image


      5 years ago

      This is great info, I'm about to get red tailed sharks, could youlist wich fish would go with it

    • torrilynn profile image


      5 years ago

      you are welcome Eric.

    • EricDockett profile imageAUTHOR

      Eric Dockett 

      5 years ago from USA

      Glad you found it helpful torrilynn. Thanks for reading and commenting!

    • torrilynn profile image


      5 years ago

      Hi EricDockett,

      thanks for this very informative hub

      that can really help current fish owners and future

      fish owners such as myself. thanks again.

      Voted up

    • EricDockett profile imageAUTHOR

      Eric Dockett 

      5 years ago from USA

      Thanks Eddy. Good luck with your fish if you decide to get them!

      @iguidenetwork: It's really the male Betta that are aggressive toward each other. There can be aggressive behaviors between male and female, (and even female/female) but generally not so much that it prevents baby Bettas. :-)

    • iguidenetwork profile image


      5 years ago from Austin, TX

      I've had a red Beta fish (or red fighting fish) before and I had a separate bowl for it from the rest of the other fish. I wonder how they mate, especially if putting them together would, probably, spark up a fight!

      I'll be on the lookout for other pet fish you've mentioned, thanks for posting.

      Voted up and useful, awesome, interesting. :)

    • Eiddwen profile image


      5 years ago from Wales

      Such a great hub. At the moment for the first time i my life we have no pets!!Landlord's rules I'm afraid .However we had toyed with the idea of setting up a fish tank. Therefore this one and others by you could come in very handy.

      Have a wonderful day and I vote up,across and share.




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