Freshwater Fish Compatibility

Freshwater aquarium fish are even more varied than saltwater fish.  They definitely have several different characteristics overall and although they do not have quite the striking colors of saltwater fish, many are amazingly colorful in their own right.  A freshwater aquarium can be every bit as mesmerizing, beautiful and colorful as a saltwater aquarium.  Furthermore, freshwater aquarium fish are far more affordable than their saltwater counterparts, plants are far less expensive than corals, and you do not have to spend money on expensive salt.  This all adds up to an aquarium system that is much more affordable to both set up and maintain.  We certainly do not want to discourage anyone away from saltwater aquariums but saltwater is definitely a bigger commitment that you need to be prepared for time wise and financially.

Like saltwater fish, freshwater aquarium fish can be passive, schooling, semi-aggressive, aggressive, or predatory.  They can also be small, medium sized, or get quite large.  There are several differences though.  There are not as many small solitary freshwater fish as saltwater fish and the schooling community fish are often smaller than the saltwater counterparts and there and far more species of small schooling fish to choose from.  There are a lot more bottom feeding and scavenger freshwater aquarium fish than saltwater fish.  There are also more types of species specific aquariums popular with freshwater tanks.

The majority of freshwater aquarium fish do well with a diet of meaty foods but most also appreciate some algae and vegetation in their food.  Most accept pellets as well as frozen foods.

The types of freshwater tanks possible are similar too but slightly different than saltwater.  Instead of a coral reef tank you can have a planted tank.  Freshwater plants are far cheaper and easier to care for than corals.  You can have community tanks, planted tanks, large predatory fish tanks, many different types of species specific tanks, brackish water tanks, mid sized fish tanks, and more.  I will review those and show some videos on the Types of Freshwater Aquariums page.

⇐Types of Freshwater Aquariums       Planted Aquarium⇒

The following lists of freshwater aquarium fish is not exhaustive but meant to provide a good overview of some of the more common types of freshwater fish and their general characteristics.  You should do more research on any specific species before deciding to integrate it into your aquarium.

Small Freshwater Aquarium Fish

Tetras/ Danios/ Rasboras/ Hatchets

tetraTetras, Danios, Rasboras, and Hatchets are all completely different types of freshwater aquarium fish genetically but they are all small passive schooling fish that do well in neutral or slightly acidic water.  Some are smaller than others and some like the Danios are more assertive than others.  They will all do well in planted and community tanks but some will hide in the vegetation more and others will be more visible.  There are literally many dozens of different species of fish in this category to choose from.  It is fine to select a few different types of fish from this category and get say 6-10 of each (depending on the tank size) and see how they interact in your tank.   They do well in groups of 4-6 in small nano tanks.  They will all do well in a well-planted aquarium with moderate lighting.  They all will like softer to neutral water (pH 7.0 or a little less)


Tiger_Barb_SchoolWe put a separate category for barbs because they are slightly larger and can be more aggressive than the other small schooling fish.  Some of them like the Tinfoil Barb get huge and could go in the Large freshwater aquarium fish category.  If you want to keep Barbs they will likely not do well with smaller schooling fish, larger peaceful fish, or fish with long fins.  They should be fine with most plants however.  They like water that is on the softer side.

Mollies/ Platies/ Guppies

mollyPlaties, Mollies, and Guppies are small peaceful freshwater aquarium fish that are related to one another and they prefer water that is more alkaline.  So they will not generally do well with fish that prefer soft, acidic water.  They are even considered brackish water fish and really prefer some salt in the aquariums, not much, about a teaspoon per gallon or so.  Platies will do fine with some salt in the tank as well and they can be good tank mates with Mollies.  Guppies have similar requirements and can have some very beautiful fins and coloration from selective breeding.  I’m not sure if they are considered “schooling” per se but they like to be grouped together.

Cory Cats

corycatEven though the Cory Cats don’t school per se, they do like to be kept in small groups.  The Cory Catfish are an ancient species of fish, they generally stay small, about 2-2.5 inches, and get along well with most other freshwater aquarium fish.  They are beautifully ancient looking and just go about their business feeding on the bottom of the tank all day long.  The prefer a neutral or slightly acidic tank and are great for planted tanks.

Otocinclus Suckermouth Catfish

otocinclusThe Otocinclus is a different type of catfish than the Cory Cats and are essential for almost any planted aquarium.  They are passive stay small and will keep all your aquarium plants free of algae.  The other option for a planted tank are Amano shrimp which will also keep aquarium plants free of algae.  They prefer neutral water and definitely like to be kept in groups.

Dwarf Gouramis

dwarf gouramiThe Dwarf variety of Gouramis are peaceful small fish that like neutral water.  They would do well in a planted tank, a small tank, or in a community tank with small schooling or otherwise very passive fish as well as with small fellow gouramis.  They should be kept in at least a small group and will stay in the middle to the top of the aquarium and so make a good contrast to most other freshwater aquarium fish.

Species Specific Freshwater Aquarium Fish



Bettas are a strikingly beautiful freshwater aquarium fish that is best kept alone.  They are very popular because they can (and should) be kept alone in a 1 gallon aquarium making them the least expensive type of fish to own.



Cichlids/ Oscars

cichlidMost Cichlids range between 3 inches to 7 inches and can come in a wide variety of colors.  They are well known for their aggressiveness and can’t really be kept with any other fish.  You can put a Pleco or a similar type fish to act as a bottom feeder/ algae eater but they will have to be larger than the cichlids and it’s best to put them in at the same time.  Cichlids have been known to gang up on and kill even large fish added to an established tank.  With names like “Green Terror” and “Red Devil” you should be clued in as to their possible viciousness towards other fish.  It can be difficult adding any new fish to an established cichlid tank. African-Cichlid-AquariumSome aquarists stock the cichlids densely to reduce their aggressiveness.  Having more males than females will help and they can usually be sexed if you know what you are looking for.  There are both New World Cichlids from the Americas and African cichlids from Africa.  The New World Cichlids will prefer more soft and neutral water and the African cichlids will require harder alkaline water.  The two types are incompatible with one another but otherwise you can generally keep a few different species in an aquarium.  Oscars are a type of Amazonian cichlid that grow to about a foot long and need a pretty big aquarium.  You will not want plants in a cichlid tank and you will want to build a back wall in the aquarium with a lot of rockwork and holes for all of the cichlids to hand out in.  When this is done well, it makes for a strikingly beautiful aquarium.


goldfish2Goldfish are a type of fancy carp bred by the Chinese a long time ago for their color and beauty.  They are one of the first types of freshwater aquarium fish ever to be kept as pets by ancient Chinese royalty.  As a carp, they are quite hardy and can tolerate fairly poor water conditions and they like their water colder than most other types of fish.  The temperature in the tank preferably should never exceed 75 degrees and do fine with it as cold as 65 degrees.  This means they generally do much better as a species specific aquarium.  They like to dig in the bottom so you don’t really need another bottom feeder.  A Chinese Algae Eater or a Pleco would do fine with some goldfish though you won’t be able to let the water get as cold as with just goldfish.  They are peaceful and can get a lot bigger than most people think, about 6-10 inches for most species.  This means they should NOT be kept in a small tank, in spite of what many people think.  Most references will say a 30 gallon tank is acceptable but we would not recommend keeping goldfish in anything less than a 55 gallon system.  In a 55 gallon tank with 3-4 goldfish and a pleco or algae eater your goldfish can grow properly and when full grown it will be a beautiful tank.  They compatible with only some hardy plants but nice gravel, artificial plants, and other decorations will also enhance the beauty of the tank.

Mid Size Freshwater Aquarium Fish


large gourami2The larger gouramis average about 6 inched full grown and are more aggressive than their dwarf counterparts.  Therefore they are better suited kept with freshwater aquarium fish of similar size and temperament although you still don’t want to put them with very aggressive fish such as cichlids.



swordtailSwordtails are a mid size freshwater aquarium fish that like more alkaline water similar to platies and mollies but they are larger, averaging about 4 inches.  They are quite passive and peaceful and could be kept with both platies as well as mollies.  Swordtails are jumpers so be sure to have a cover on your tank or a canopy that completely surrounds the aquarium.  Males can be aggressive towards each other so they are not strictly schooling fish but prefer to be kept in groups with a male and a few females.


rainbowfish2Rainbowfish are a mid size freshwater aquarium fish that like neutral water and average about 3-4 inches.  They can be pretty colorful and so make an attractive addition to a community or planted tank  They are generally quite passive and peaceful.  Males can be aggressive towards each other so they are not strictly schooling fish but prefer to be kept in groups with a male and a few females.


fw angelfishFreshwater Angelfish are not the same as their saltwater counterparts although they bear some superficial resemblance.  They like softer acidic water but will do fine in neutral water.  They are semi-aggressive and reach a fairly good size of about 6 inches when full grown.  Even though they are larger they will do well in a freshwater community planted tank with small schooling fish and so are great for any mid size or larger size planted aquarium.  They prefer to be kept in groups and are not solitary fish.  They are probably not a good tank mate for discus though which are similarly sized but more passive.


discusDiscus are a beautiful freshwater aquarium fish and they command prices similar to saltwater fish due to their beauty and bold colors.  The reach up to 8 inches in size but are very passive.  They do well with other passive tank mates and will do well in a community planted aquarium with small schooling fish. They prefer to be kept in groups and are not solitary fish. Many people keep Discus only tanks although they will get along fine with other passive fish.  They need very high water quality and so a filter like the Aquaripure nitrate removal denitrator filter will really help make a discus tank more manageable.


loachLoaches are active bottom dwelling scavengers ideally suited for the community aquarium. Loach fish consist of some of the most popular of all tropical freshwater aquarium fish, adding color, interest, and beauty to any larger community aquarium. Loaches are semi-aggressive fish when housed in the aquarium individually and prefer to be kept in small groups up to 6 or more.   Some types like the Clown Loach get quite large, up to 1 foot long.

Smaller Plecos

bushynoseplecoMany species of plecos such as the Bushy Nose Pleco and Rio Negro Pleco stay in the 4-6 inch range and are suitable for smaller tanks.  Make sure you find out the specific species of pleco and be 100% certain that it won’t get to large before you put it in a smaller aquarium.  They do well as a solitary freshwater aquarium fish.

Smaller Freshwater “Sharks”

red sharkThe smaller “sharks” such as the Redtail shark make for a good mid size freshwater aquarium fish.   Freshwater Sharks prefer aquariums that contain several hiding spaces, along with driftwood and larger thick leaved plants. No relation to marine sharks, these curious fish make a wonderful addition to the semi-aggressive aquarium by adding a great deal of personality and character.  They do well as solitary fish.

Silver Dollar

silver dollar2The round shape and silver color of its body lend the Silver Dollar a very appropriate name. With a maximum size of 6″, they are perfect for the larger community aquarium.  Silver Dollars are a lively schooling fish and best kept in groups of at least three or more. Rocks, plants, and driftwood help mirror its natural habitat and will help to reduce stress on the fish, though plastic plants may be necessary due to their herbivorous nature. They do best in soft, slightly acidic water with good filtration.

Large Freshwater Aquarium Fish


BichirBichirs are primitive ray-finned fishes collected from Africa. They are opportunistic feeders and should be housed with large, peaceful freshwater aquarium fish. They can breathe air using a lung-like modification to their swim bladder and can travel on land for short periods of time using their strong pelvic fins. Their aquarium setup should include a tight fitting lid and adequate bottom space. 

Suckermouth Cats/ Plecos

PlecoSuckermouth Cats are great algae controllers for any peaceful or semi-aggressive aquarium.  Plecostomus, or Plecos, are a type of suckermouth catfish that have specially adapted mouthparts, enabling them to attach to substrate. Most Plecos are peaceful freshwater aquarium fish and prefer to rest or slowly graze over the aquarium bottom, and do an excellent job of cleaning unwanted algae from the bottom and sides of the tank. They are both great additions for many freshwater aquariums to help reduce the amount of maintenance your aquarium requires.  There are some dwarf varieties but be aware that many of them get quite large, up to 1 foot in length.  They do well as solitary fish.

Large Freshwater “Sharks”

bala_sharksThe Bala and Columbian sharks are good fish for a large freshwater fish aquarium.  Freshwater Sharks prefer aquariums that contain several hiding spaces, along with driftwood and larger thick leaved plants. No relation to marine sharks, these curious fish make a wonderful addition to the semi-aggressive aquarium by adding a great deal of personality and character.  They do well as solitary fish

Miscellaneous Large Fish

arowanaTin Foil Barbs, Arowanas, Fahaka Puffer, Siamese Tigerfish, Prehistoric Dragon Goby, Redfin Prochilodus, Freshwater Eels, and Ropefish are all freshwater aquarium fish that can get over a foot long in size.  Some, like the Fahaka puffer, are generally best kept alone in it’s own tank.  Others can be housed with other big fish making for a very cool display but you will need a BIG tank for something like that.  A tank in the 250-400 gallon range can house several big of these boys.

Brackish Freshwater Aquarium Fish

pufferBrackish fish originate from areas in which freshwater meets saltwater. Fish that live in these areas are able to tolerate a wide range of salinities. Brackish fish do best in water with some salt in it and can usually be acclimated to a range but need at least some salt.  A salinity of up to 1.015, or 1/4 cup marine salt per gallon, is recommended along with a pH that is more alkaline, around 7.5 to 8.4.

Mollies are a schooling brackish water fish.  Mollies have the ability to adapt to a variety of salt levels in the aquarium. With a gradual acclimation, these fish may be maintained in either a freshwater or saltwater aquarium. In the freshwater aquarium, at least a teaspoon of aquarium salt per gallon is recommended for optimum health.  When you do this swordtails and platies can make good tank mates.

Scats, Columbian Sharks, Figure 8 puffers, the prehistoric Dragon Goby are all examples of brackish water fish, some of which can get over a foot long.

There are some plants that will do well in a brackish water aquarium.

⇐Types of Freshwater Aquariums       Planted Aquarium⇒

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