10 Best Fish for a 40 Gallon Tank

Ahh, the 40-gallon tank. Tanks that are this size are often categorized as being either a "breeder tank" or just a standard 40-gallon. The main difference between a breeder tank and a standard tank is that breeder tanks tend to be wider and shorter in depth. Breeders tend to be a bit easier to clean, as the shorter depth allows for more maneuverability during routine maintenance. However, hobbyists don't need to exclusively breed fish in a breeder! There are tons of stocking options for both breeder and standard 40-gallon tanks.

If you're looking for some stocking inspiration, then you're in luck! In this post, we'll recommend 10 of our favorite stocking options for a 40-gallon aquarium.

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Schooling vs Centerpiece

If you're familiar with some of our existing best-of lists, such as our 10 Best Freshwater Fish for a 75-Gallon Aquarium, then you may already know that we like to briefly cover the differences between schooling and centerpiece fish.

While some hobbyists may prefer to house a few larger-sized fish in bigger tanks, don't sleep on the opportunity to house a large school of smaller fish. Seeing a large school of small fish moving in unison is a sight to behold in an at-home aquarium, and hobbyists have plenty of options to choose from when it comes to nano-sized fish. Regardless, in this post, we'll cover both small and larger-sized fish for a 40-gallon.

Neon Tetras

Starting off our list is the classic Neon Tetra. This fish has also earned a spot on our list of Best Fish for a 20 Gallon Tank, so it's no surprise to see it making an appearance here. A 40-gallon tank gives hobbyists plenty of room to house up to 30 of these fish, and aquarists will appreciate their bright blue and red coloration.

Kribensis Cichlid

Hobbyists interested in keeping cichlids can consider the Kribensis Cichlid in a 40-gallon, but only if they can acquire a mated pair. Males tend to show hostility towards one another, so an established male/female is crucial. These fish are easy to breed in captivity and are sexually mature at about the 8-month mark. If you're interested in breeding these fish, make sure you have a plan for the offspring.

Bolivian Rams

Next up on our list are the Bolivian Rams. Similar to the previously mentioned Kribensis Cichlid, hobbyists are locked into a male/female combo in a 40-gallon tank. Males will show aggression towards one another, so you must have a mated pair. While it can be difficult to find a mated pair for sale, it's worth phoning up your local fish store or taking a look on our marketplace, to see if you can find a few for sale. These fish do breed in captivity, so don't be surprised if you end up with some baby fish swimming around your tank.

German Blue Rams

Hobbyists interested in keeping rams will be happy to know that they can keep a few German Blue Rams in a 40-gallon, but knowing the gender is crucial. Hobbyists can keep two mated pairs, totaling 4 fish in their 40-gallon tank. Compared to other rams, German Blue's tend to be peaceful and are excellent fish for those looking to get into ram-keeping.

Green Dragon Bristlenose Pleco

Pleco keeping is a world of its own, with a unique species categorization system developed by the German aquarium magazine DATZ, there is no shortage of plecos to choose from. One of our favorites has to be the shortfin or longfin version of the Green Dragon Bristlenose Pleco, and hobbyists shouldn't have any issues keeping the species in a 40-gallon tank. Hobbyists should be aware that they live for quite a long time, up to 12 years in captivity, and are big eaters - so staying on top of your routine tank maintenance is crucial!

Juvenile Flowerhorn Cichlid

Ahh, the controversial Flowerhorn Cichlid. These fish are sought after for their large nuchal humps, which give them an exotic appearance. The species is one of the most cross-bred in the hobby, so hobbyists may want to think twice before pursuing the fish as their next tank addition. Still, for those who are interested, a single juvenile flowerhorn can exist comfortably in a 40-gallon, but once it fully matures, you'll want to move it to a 50-gallon aquarium. We cover the care of the fish in more detail in our guide, Red Dragon Flowerhorn Cichlid: Care, Lifespan, Breeding & More.

Emperor Tetra

Hobbyists looking for a tetra with a lot of personality should strongly consider the Emperor Tetra. These fish are slightly larger than the previously mentioned Neon Tetras and are much more active throughout the tank. These fish sport a dark purple coloration and are easy to care for. Hobbyists may also want to consider the line bred Blue Emperor Tetra, while this fish is a bit harder to find, its brilliant blue coloration is nothing short of stunning.

Celestial Pearl Danios

Myanmar is home to some of the most brilliantly-colored species in the aquarium hobby. Zebra Danios, Sulawesi Shrimp, and the famous Celestial Pearl Danios are all native to the Asian country, but CPDs (also referred to as Galaxy Rasboras) are arguably the most popular. These fish sport a brilliant, galactic coloration, and hobbyists will love their iridescent speckles. Hobbyists can keep up to 30 of these in a 40-gallon tank, and they make for excellent schooling fish.

Platinum Blue Medaka Ricefish

Ricefish are known for their ability to thrive in cold water conditions, making them a unique consideration for hobbyists looking to stock a cold water 40-gallon tank. These fish native to Japan, are named after their rice-like appearance, but a unique color strain, known as "Platinum Blues", is always in demand by hobbyists in the know. Hobbyists should have no issues keeping 30 of these fish in a 40-gallon.

Green Kubotai Rasboras

Hobbyists looking for a green-colored fish, should look no further than the Green Kubotai Rasbora. These rare rasboras are one of the few green-colored fish in the hobby, and their small size makes them an excellent option for aquarists looking to house a large school of them. Hobbyists can keep up to 25 of these in a 40-gallon, and they pair beautifully with red-colored aquatic plants.

Conclusion

That concludes our list of 10 best fish for a 40-gallon tank. As you can see, whether you decide to house a few large-sized fish or a school of nano-sized fish, there is no shortage of options to choose from. Did you have a favorite fish that didn't make the list? Let us know in the comments, and be sure to visit our marketplace, where you can shop some of these fish for sale by other hobbyists.