7 Best Fish for a 55 Gallon Tank Or Aquarium – Interesting Choices!

With a 55-gallon aquarium, you have a vast variety of stocking options at your disposal to create a tranquil and mesmerizing display.

With so many choices to make, it can be challenging to sort through all the information on the available species suitable for a tank of such size, their stocking numbers and tankmate compatibility.

The best fish for a 55 gallon tank written beside a large, calico colored fish

To save you from potential disasters, we’ve compiled below a comprehensive list of the most popular and best fish for a 55 gallon tank, detailing who they can co-exist with and everything you need to enable them to thrive in a healthy ecosystem.

Let’s dive in…

Before You Buy – Consider This!

The 55-gallon tank has a considerable amount of space to keep some really amazing-looking fish. When you’re dealing with a tank of this size, there’s less chance of making stocking errors, commonly made with smaller fish tanks. (And if you’re still looking for the perfect model, check out our guide to the best 55 gallon fish tanks!)

This sized aquarium allows you to keep single tailed goldfish, or a couple of beautiful fancy goldfish, or a whole range of dazzling and entertaining schooling fish.

However, not every species can live happily together, and it’s important you learn as much as possible about how to care for your fish and aquarium – that way you’ll have the best chance at establishing a healthy ecosystem for your fish.

Before stocking your 55-gallon tank, you’ll need to consider the adult size and personality of the fish. Some of the smallest fish can be the most aggressive. Other fish not kept in large enough groups will fail to thrive and become depressed. The more you know about your fish and aquarium, the more success you will have.

How Many Fish Can I Have in My Tank?

If you have no intention of upgrading from a 55-gallon tank, considering the adult size of your fish, rather than the size they are at the time of purchase will save you from many stocking issues.

Every fish and invertebrate produces what’s referred to as ‘fish load.’ This individual ‘load’ has an impact on the ecosystem of your aquarium. The equilibrium of the tank is determined by the number of plants, fish waste, and oxygen levels – with the more significant the tank – the easier it is to achieve a balance.

To be able to determine how many fish to keep in your 55-gallon aquarium, there are two rules you can use to guide you:

One Inch of Fish Per Gallon Rule

This is broadly used to calculate one inch of fish per gallon of water in the tank.

On the surface, this rule looks feasible, but it fails to account for the different shapes of fish, as well as anything else you may have in the tank.

Only use this rule as a rough guide and in doing so, be aware of the real amount of water in the tank after you’ve placed any plants, decorations, filters, and fish. The more extras – the less water.

The Surface Area Rule

The surface area rule allows for the various tank shapes available – with many tanks producing different surface areas. The larger the surface area, the more water is in contact with air at the surface, and the more carbon-dioxide and oxygen is exchanged, meaning higher amounts of oxygen in the water for fish to breathe.

The amount of oxygen being exchanged directly impacts how many fish your tank can sustain.

A tall, narrow tank may hold the same amount of water as a broader, low tank; however, the amount of water exposed at the surface is considerably different.

The calculation is 1 inch of fish per 12 inches of surface area. When applying this rule, you need to modify that calculation to allow for the varying body shapes of your fish:

  • 1 inch of ‘slender’ fish per 12-inch surface area
  • 1 inch of ‘full-bodied’ fish per 20-inch surface area
  • Somewhere in the middle would account for ‘medium-bodied’ fish.

Tankmates – Friend or Foe?

Before deciding to stock one type of fish with another, it’s vital you educate yourself on how compatible particular fish are with others.

For a full list of compatible fish, please see the freshwater fish compatibility chart and the marine fish compatibility chart.

The Best Fish for a 55 Gallon Tank

Angelfish (Pterophyllum Scalare)

Close up of 2 angelfish

  • Origin: South America
  • Maximum size: 6 inches
  • PH of water required: 5-7.5
  • Diet: Omnivorous; bloodworms, brine shrimp, flakes, vegetables

The angelfish is a favorite occupant of a 55-gallon tank due to its spectacular looks and fascinating behavior. It sports an unusually-shaped body, a variety of colors and can grow up to six inches long. Angelfish can be moderately difficult to care for and not usually recommended to novice fish-keepers.

Angelfish will eat anything, so it’s essential you don’t overfeed them. Only feed them once per day with a balance of frozen and fresh food; mainly in the form of high-quality flakes, brine shrimp, and vegetation.

The expected lifespan of the angelfish is more than a decade – provided their tank conditions are appropriate.

It’s not recommended you keep it in less than a 30-gallon tank, with 55-gallons being the most desirable.

Only fill your aquarium with soft-edged decorations to protect their sensitive bodies and ensure any plants you use contain large, broad leaves for the angelfish to lay their eggs.

Angelfish aren’t too particular about their substrate; however, something dark and finely ground – suitable for healthy plant growth should suffice.

When it comes to tankmates, angelfish do have the potential to display aggressive behavior towards smaller species. You’ll need to stock it with medium to larger-sized fish such as swordtails, mollies, and platyfish and refer to the general fish stocking rules to determine how many to keep in a 55-gallon tank.

Keep the filtration moderate, as anything more has the potential to stress your angelfish out and fail to thrive.

Harlequin Rasbora (Trigonostigma Heteromorpha)

Close up shot of a harlequin rasbora in a planted tank

  • Origin: Southeast Asia, Singapore, Malaysia, Thailand
  • Maximum size: 1.75 inches
  • PH of water required: 6.0-7.0
  • Diet: Omnivorous; flakes, pellets, mosquito larvae.

Due to their ease of care and stunning metallic coloring, the Harlequin rasbora is widely loved by aquarium enthusiasts. The Harlequin rasbora has a copper-red body with a black triangle-shaped chunk covered its lower region. As a mostly peaceful species it can really liven up your tank when kept in large schools – but due to the vividness of its color, need to be kept away from larger fish to avoid being eaten.

It should be kept in schools of eight or more. Harlequins are peace-loving community fish that show no aggression to any other fish or invertebrate. Some suitable tank mates would be neon tetras, dwarf gouramis, small barbs, danios and cory catfish. They do well in a tank with a lot of thick live foliage, dark substrate, diffused lighting and plenty of open space for swimming.

You can feed them almost anything and are happy to accept flake, in addition to any other frozen, fresh or dried food. Focus on plenty of variation to avoid digestive issues or disease.

You can determine the sex of harlequins by the males being slimmer than their female counterparts, with their black triangle chunk on their lower half; whereas, the female sports black chunk is entirely straight.

Zebra Danios (Danio Rerio)

A zebra danio

  • Origin: Eastern India
  • Maximum size: 2 inches
  • PH of water required: 6.5-7.0
  • Diet: Omnivorous; will eat most food but love small invertebrates and fresh vegetable matter.

You can easily spot the zebra danios by their beautiful black and white striped bodies. Active swimmers, zebra danios are easy to care for due to their durability and ability to handle a large range of water conditions and temperatures.

Zebra danios are schooling fish; therefore, should never be kept singularly. They live happily in groups of at least five.

A 55-gallon tank is an ideal size for housing a large school of zebra danios but to get a better idea of how many in the group, referring to the commonly used rules will help guide you.

They will co-exist peacefully with most other species but are prone to nipping the tails of fish such as guppies and angelfish out of boredom. You might consider stocking them with swordtails, loaches, and barbs.

Due to their high level of activity, despite preferring the top of the tank, they will explore the whole tank. For this reason, these fish require plenty of open spaces to swim, with plants around the edges and evenly distributed lighting.

Using a dark substrate will enable you to highlight their color and provide a natural environment.

Fancy Goldfish (Carassius Auratus)

White and orange fancy goldfish with huge fins and a wen hood

  • Origin: A domesticated version of carps from East Asia
  • Maximum size: 10 inches
  • PH of water required: 7.2-8.0
  • Diet: Omnivore; high-quality pellets, vegetables, with some fresh or frozen bloodworms, brine shrimp, mosquito larvae.

Fancy goldfish come in many shapes and sizes; are rounder than common goldfish and have flowing double tails. Although the most common color is basic orange, they are also available in many tropical colors.

The most striking attribute of the fancy goldfish is, however, their unusual look – arrived at as a result of selective breeding processes. They are sometimes recognizable by their huge bulging eyes, or oddly shaped heads depending on exact species, and although some can resemble the common goldfish – some forms of selective breeding have resulted in the most extreme versions.

Fancy goldfish need at least 20 gallons of water per fish with a robust filtration system and regular water changes. Fancies will grow up to around 10 inches long and produce a lot of waste. To avoid disrupting the ecosystem and risk high levels of ammonia (which will cause your fish many health concerns), you should keep it in a large, rectangle-shaped tank. Ideally, you should use an external filtration system with adequate space for biological filter material.

Fancy goldfish have a reputation of being awkward and bumping into fixtures. For that reason, don’t place any sharp-edged decorations in the tank. Robust plants and a sand substrate (if any) are preferable.

Being community fish, they shouldn’t be kept on their own for long. Long periods of solitude will result in feelings of vulnerability and high levels of stress. They need to be stocked in a minimum of pairs. As for other tankmates – there’s a massive risk they’ll eat smaller fish; therefore, you’re better off keeping a single species tank.

Your fancy needs a diet of high-quality pellets, vegetables, with some brine shrimp, bloodworms or mosquito larvae (fresh and frozen). Feed them in small portions, spread evenly throughout the day.

Fancies have great personalities and provide a lot of entertainment in the aquarium. They are naturally inquisitive and animated – and will play with their owners by pleading for food once they are used to them. You’ll never tire of owning a fancy goldfish.

Swordtail (Xiphophorus Hellerii)

A shiny metallic swordtail

  • Origin: Honduras and Central Mexico
  • Maximum size: Up to 6 inches
  • PH of water required: 7.0-8.0
  • Diet: Omnivorous; high-quality fish flakes and greens

Swordtails are a great starter fish requiring a minimum of 30 gallons of water. Their primary requirement when it comes to tanks is the length, as they need broad areas of water to swim in. Placing them in confined spaces will cause them distress and force them to go against their peaceful nature.

Ensure your tank also has a tight hood to avoid your swordtail jumping out of the aquarium as due to the speed of their swimming capabilities, jumping is frequently an issue.

To provide an environment similar to their habitat, fill the tank with tall, robust live or plastic plants – although live plants will naturally increase the quality of water and have an oxidizing effect.

Swordtails require heavy filtration due to their bioproduction. Look for something large and powerful you can hang over the back of the tank to avoid taking up too much space in the aquarium. The more you keep in the tank, the more you’ll need to change the water to prevent ammonia spikes.

This is a resilient fish who can live with many other fish species, compatible with the same water conditions. These include catfish, mollies, platyfish, and tetras.

Swordtails have a strong preference for dominating other male swordfish; and for that reason, need to be kept in a school of predominately female – usually with one male to four female ratios. This allows the majority female pack to take most of the male’s focus – getting rid of the need to fight with other male swordtails.

If you follow the, one inch of fish per gallon of water rule, one male to four females would be ideal for less than 55-gallon tanks.

Mollies (Poecilia Sphenops)

2 black mollies foraging at the bottom of a planted tank
© kocsisanyi78 – stock.adobe.com
  • Origin: Central and South America
  • Maximum size: 4.5 inches
  • PH of water required: 7.0-8.0
  • Diet: Omnivorous; herbivore pellets can be combined with frozen foods such as mosquito larvae and fresh blanched vegetables like spinach.

Mollies are amongst the most popular fish for aquarium enthusiasts with the females growing to around three inches and the males reaching 4.5 inches in size. They come in various patterns and colors with the most common being jet black.

Mollies make excellent fish for beginners due to their relative ease of care. However, due to lack of knowledge regarding aquarium requirements, they often die sooner than necessary.

Mollies need to be kept in at least 30 gallons of water and should in a minimum of three – making up one male to two females. They do relish in being in large schools; therefore, refer to the one inch of fish per gallon of water rule, to estimate the maximum number suitable for your 55-gallon tank (for a single-species aquarium).

Mollies require a filtered, heated and fully cycled tank and prefer hard water to ensure their health. They’ll need a lot of places to hide but you should also allow for enough open spaces to swim without restrictions. A long rectangular tank is ideal for mollies.

As extremely active fish, mollies can nip other species and are best kept separate from calmer species and those with long flowy tails. If you want to set up a community tank, consider introducing your mollies to cherry barbs or other livebearers.

Feed them a plant-based diet of vegetarian pellets with a balance of fresh greens and mosquito larvae.

Bristlenose Pleco (Ancistrus Cirrhosus)

A bristlenose pleco on the bottom of a gravel lined tank
© Mirko Rosenau – stock.adobe.com
  • Origin: South America
  • Maximum size: 5 inches
  • PH of water required: 7.0-8.0
  • Diet: Mostly herbivorous; algae, vegetables, plant-based pellets.

As one of the tiniest catfish available to purchase, the bristlenose catfish can be differentiated from the common pleco by its broader head and shorter, fuller body. They are an excellent suckerfish, made possible by their round-shaped mouth and drawn-out lips. Their bodies are either green, brownish-black or grey in color with pale spots.

They can be found at the base of the aquarium or suckling the interior walls – a fascinating sight. They are incredibly peaceful and remarkably resilient making them perfect for novice fish-keepers.

In regards, to stocking the bristlenose, the males do exhibit very territorial behavior and therefore, shouldn’t be kept together.

As a nocturnal species, you’ll need to keep their tank filled with hiding places in the way of caves and driftwood for them to rest during the day and ensure it has plenty of oxygen with a medium flow of water.

In a single species tank, you’ll need to apply the one inch of fish per gallon rule as a rough guide, but they do require a minimum of 25-30 gallons of water and need a long, broad tank. Only use sand in their tanks as gravel will cause injury to their bodies.

Bristlenoses thrive on a predominantly herbivorous diet. They eat a lot of algae which is ideal for keeping your aquarium clean. Be sure to focus on feeding them a nutritious balanced diet and don’t just rely on the tank’s algae. You can feed them blanched vegetables in addition to pellets or wafers designed for herbivores – just make sure they are the sinking type.

You’ll know they’re getting enough nutrition by their coloring – dullness is an indication of a nutritional deficiency.

Wendy Kathryn

Hi, I'm Wendy, the owner and creator of this website, an experienced fish keeper and avid student of the art since 2010. My aim is to help beginners avoid the many possible mistakes when getting started in this wonderful hobby.

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