5 Best Fish Tank Ideas for a 40-Gallon Breeder Aquarium

The 40-gallon breeder aquarium is a very popular size because of its 36” length x 18” width x 16” height (91 x 46 x 41 cm) dimensions. Other 40-gallon tanks have a more rectangular base, but the 40-gallon breeder tank has a deeper base without being too tall so that you can easily reach inside to clean the aquarium and catch fish that you have bred. The 18-inch width also lets bigger fish to turn around more easily, making this one of the first footprints that allows you to keep either a larger solo specimen or community of fish. Keep reading to learn about our top 5 fish stocking ideas for a 40-gallon breeder tank.

1. The Flowerhorn Tank

Flowerhorn cichlid

This hybrid New World cichlid is known for having jaw-dropping, colorful patterns and a large nuchal hump that grows on the heads of males. Flower horn fish are especially valued in certain Asian cultures because they are thought to bring good luck and prosperity. While flowerhorns are quite playful and personable towards their human owners, they can be fairly aggressive toward other smaller animals in their territory. Therefore, we recommend only keeping one in the 40-gallon tank with no other tank mates. When it gets bigger, your wet pet will eat lots of food and therefore need more water changes to keep the water clean. After a few years of enjoyment in the 40-gallon breeder, we recommend eventually upgrading to a 55- or 75-gallon aquarium to accommodate its impressive, adult size.

2. The Community Aquarium

Bolivian rams, julii corys, and black skirt phantoms

If one showpiece fish per tank is not your idea of fun, let’s go the opposite direction and fill the 40-gallon tank with many different species. First, we want to get one to three pairs of Bolivian rams (Mikrogeophagus altispinosus). They are known for their beautiful, trailing fins and will serve as the 3-inch (7.6 cm) centerpiece fish for this community tank. To minimize territorial disputes, make sure to provide plenty of aquarium plants and decorations to block line of sight. Then add a school of julii corydoras that will help clean the fish tank by constantly scavenging for leftover food stuck in the substrate. Since you have a medium-sized aquarium to work with, choose a stockier, midlevel schooling fish. We like black phantom tetras (Hyphessobrycon megalopterus) because of their strikingly high dorsal fins.

All of these fish are pretty hardy, live in similar water parameters, and are safe with aquatic plants. Plus, they eat a similar omnivore diet of community foods, such as frozen bloodworms, pellets, and Repashy gel food. This initial stocking list forms a basic foundation for your 40-gallon community tank. Feel free to spice it up with some of your personal favorites — like a rare pleco, snails, rainbow shark, or some oddball fish.

3. The “Breeding for Profit” Tank

Female albino long fin bristlenose pleco

With a 40-gallon breeder aquarium, there are of course many species that you can try spawning, such as long fin bristlenose plecos. This catfish runs between 4–5 inches (10–13 cm) long but has giant finnage that takes up more space than normal bristlenose plecos. They also require bigger caves to accommodate their wider wingspan. You can breed them in a smaller aquarium, but once they start producing lots of fry, you will have to regularly move the offspring to other fish tanks.

For filtration, we like to use gentle sponge filters to keep the babies from being sucked up by accident. Then we condition the adults for breeding by feeding plenty of their favorite foods, like Repashy gel food, sinking wafers, bloodworms, and blanched zucchini. The fry have smaller mouths and often like to graze on driftwood, algae, crushed flakes, live baby brine shrimp, and canned green beans.

Long fin bristlenose plecos come in many varieties — such as albino, green dragon, chocolate, and super red. Start a relationship with your local fish store and find out which types have the highest demand so that you can sell your juvenile plecos to them. For more information, see our article on breeding fish for profit.

4. The African Cichlid Tank

Male and female saulosi cichlids

Most African cichlids require larger fish tanks, but the saulosi cichlid (Chindango saulosi or Pseudotropheus saulosi) is a dwarf mbuna from Lake Malawi that only grows up to 3.5 inches (9 cm). They are very visually stunning because of the sexual dimorphism between males and females that makes them look like two different species. The dominant male is a vivid blue with dark, vertical striping, whereas the females are a solid sunshine yellow. Subdominant males tend to range from yellow to light blue with faint barring.

For a 40-gallon aquarium, we recommend getting 1–2 males and 4–5 females. As with most Lake Malawi cichlids, they require high pH, GH, and KH, as well as a diet high in vegetation and roughage. They also need lots of rocks and hiding spaces to minimize territorial disputes. Saulosi cichlids are very easy to breed, and you may see some of the females holding eggs in their mouths until the fry are free-swimming. You can either remove the fry into a separate grow-out tank or let them hide in the rockwork until they are big enough to fend for themselves. If you are looking for a fun and enjoyable aquarium setup that rivals the brilliant colors of saltwater tanks, then you have to try this dwarf mbuna.

5. The Rare Fish Colony

Trout goodeid

For our last stocking choice, we chose the trout goodeid (Ilyodon furcidens), a rarer type of livebearer from Central America that looks like a 3.5-inch (9 cm) miniature trout. Like most livebearers, they prefer higher pH and GH, but they are a bit unusual because they require temperatures cooler than 72°F (22°C). Thankfully, they are not picky eaters and eagerly eat flakes, pellets, and even hair algae in your planted aquarium. You could mix them with other fish, but we like experiencing them as a single-species colony to see the unique behaviors that come out when they’re only surrounded by their own kind. Another good usage for a 40-gallon breeder aquarium would be conservation of endangered fish species. If you are interested helping to preserve at-risk fish, search online for the “CARES Preservation Program” to find out more.

Hopefully, these 40-gallon aquarium profiles have inspired you in the hobby. We have many more stocking ideas for 10-gallon and 20-gallon tanks for you to check out as well. While Aquarium Co-Op does not ship fish, you can see our list of preferred online vendors that sell aquarium animals. Best of luck and enjoy nature daily!