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What Fish Cannot Live Together?

Fish have different ways of communicating with each other, and they can be easily misinterpreted by some species. This works similarly to humans encountering somebody who does not speak the same language as them. 

Certain signals can be translated as other to mean something else. In addition to different amounts of space, quality of water, and food requirements, you must be researching how compatible a specific species of fish is with your current fish. Check out for information about caring for your fish. 

These are some of the most territorial fish that should be kept alone if possible. 

Flowerhorn Cichlid

Firstly, these highly ornamental fish were in high demand many years ago. They come in bright colors and are easy to spot because of their unusually shaped head. Unfortunately, flower horn cichlids are not suitable to be put with most other species of fish. 

This is because, like most cichlids, flower horns tend to be very aggressive in general. However, these fascia fish are entertaining when they are kept in the right environment. They have been known to interact with humans and put on a show on occasion. 

Red Tail Shark

Another exotic species that you may want to add to your collection is the red-tail shark. They can become aggressive if they are not given enough space and decorations to explore. Because of this, redtail sharks are not recommended for beginner aquarium owners. 

They like to dart back and forth at the bottom of the tank, and they can become aggressive towards you and other fish if this isn’t provided. 

Dwarf Pea Puffer

This species will surprise you with how aggressive it can be. Despite their adorable appearance, dwarf pea puffers tend to fight with other fish. They work well with members of the same species, but still, need enough space for alone time when needed. 

They will also need to be kept occupied with plenty of tank decorations and things to stimulate them. Plants, hiding spots, driftwood, and rocks are recommended if you want to keep this curious species entertained. 

In general, dwarf pea puffers are not ideal for those with other species of fish due to their aggressive tendencies. 

Black Wolf Fish

Also known as hoplites Curupira, the black wolf fish is another species that is not recommended to keep with other species because they are predators. This means that they are likely to take a bite or fight with smaller fish in an aquarium. 

The black wolf fish prefer warm temperatures of water and relatively neutral pH. They tend to be a good fit with similar-sized, fast-moving, and aggressive fish, but there is always a risk of them fighting. Consider keeping a black wolf fish separate if possible. 

After Knife

A freshwater fish that can reach 31” in length is the after the knife. These creatures are also very predatory, and it is recommended that they are fed live prey or feed. This means that they are more likely to become aggressive towards smaller fish if they are not being fed enough. 

Predatory Fish

As a general rule, it is recommended that you avoid adding a predatory fish to your aquarium. This is because they are prone to eating anything that will fit in their mouths. Although this doesn’t necessarily make them aggressive, predatory fish can eat smaller fish in an enclosed space if they are hungry. 


Because of that, they are not recommended to be kept as pets, especially for beginners. Some of the predatory fish which are less well-known include gar, catfish, leaffish, needlefish, halfbeaks, and stingrays. 

Breeding Fish

Another factor to consider when you are looking for a new addition to your aquarium is whether you have any fish that are breeding. Certain species can become very defensive and even controlling in some cases when they are breeding. As a result, they can become very distressed if you decide to add another species into the mix. 


If you are unsure about adding a particular species to your aquarium, then it is recommended that you speak with an expert. You should also do your research to figure out any possible risks that can happen if you introduce a certain species into your aquarium. 

Remember that each species has its preferences and requirements, and it is not worth rocking the boat in most cases. This means getting species that are more docile and easy-going to avoid aggressive behavior. 


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