23 Best Fish for a 20-Gallon Tank: A Curated List

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Last Updated: August 30, 2023 by Flora Gibbins

Having spent decades navigating the intricacies of fishkeeping, I can attest that a 20-gallon tank strikes an ideal balance — it’s spacious enough for a rich tapestry of aquatic life yet manageable enough for both novices and seasoned enthusiasts. But beware: choosing the right fish species isn’t just a shopping spree. It’s more akin to composing a living mosaic where each fish contributes to a harmonious, thriving ecosystem.

That’s why I’ve prepared this definitive guide, meticulously choosing 23 best fish for a 20-gallon tank. We’ll also delve into essential factors like temperament, water parameters, and even recommend some captivating combinations to jumpstart your fishkeeping journey. Ready to embark? Let’s get started.


The 23 Best Fish for a 20-Gallon Tank

1. Neon Tetra (Paracheirodon innesi)

neon tetra

  • Common Names: Neon Tetra, Neon Fish
  • Adult Size: 1.5 inches
  • Water Parameters: pH 6.0-7.0, Temperature 70-81°F

A radiant gem within the aquarist’s palette, the Neon Tetra is far more than just a splash of color. When you see these iridescent beings—their vivid blues juxtaposed with fiery reds — darting in a perfectly coordinated school, it’s nothing short of mesmerizing. A single Neon Tetra is eye-catching; a school of them is a hypnotic choreography that adds dynamic movement to any 20-gallon setup.

These South American natives are not merely for show; they’re resilient in their natural habitat, and in captivity, they are amenable to a variety of tank mates and adaptable to various aquascapes. Picture them weaving through lush aquatic plants, maneuvering around driftwood, or emerging from shadowy caves—a dash of brilliance against nature’s complex backdrop. Their presence provides a living, moving art piece that complements intricate and thoughtfully designed aquariums.

Perhaps their most compelling feature is their gentle temperament. Neon Tetras are quintessentially community-oriented, adding serenity to your underwater world. When kept in groups of six or more, these schooling fish help create a tranquil yet visually striking environment.

Indeed, opting for Neon Tetras isn’t merely a choice; it’s an artistic and emotional investment that pays off in a constantly evolving tableau of aquatic beauty. With these dazzling inhabitants, your tank will not just be a container of water, but a living canvas that captivates all who gaze upon it.

2. Guppy (Poecilia reticulata)

guppy care

  • Common Names: Guppy, Millions Fish, Rainbow Fish
  • Adult Size: 1.5-2.5 inches
  • Water Parameters: pH 6.8-7.8, Temperature 74-82°F

This is a fish that has beguiled aquarists for generations with its kaleidoscopic array of colors and patterns. Each Guppy is a unique spectacle; males, in particular, boast resplendent caudal fins that unfold like ornate fans. Imagine your 20-gallon aquarium graced by a living confetti of vibrant hues — azure, vermillion, gold — each Guppy a tiny masterpiece darting through the water.

Beyond their striking visual appeal, Guppies are beloved for their minimal care requirements, making them an ideal choice for both experienced and novice fish rykeepers. These viviparous livebearers reproduce with astonishing speed and ease — meaning your tank can swiftly transition from a few fish to a bustling aquatic community.

But what truly stands out is their adaptive nature. Guppies harmonize well with other peaceful fish species, displaying an affable demeanor that transforms your tank into a congenial underwater society. This is vital, especially in a 20-gallon setup, where real estate is limited but opportunities for interspecies interaction are abundant.

If you’re drawn to the idea of experimenting with fish breeding, Guppies provide an excellent introduction. Their frequent reproductive cycles offer an intimate look at the miracle of aquatic life, evolving your 20-gallon tank from a mere display into a thriving, regenerative ecosystem.

Ultimately, adding Guppies to your setup isn’t just about filling space; it’s about introducing complexity, dynamism, and an element of surprise. Their vivacious spirit and stunning diversity make them a living testament to the sheer variety and wonder of aquatic life.

3. Betta Fish (Betta splendens)

delta tail betta

  • Common Names: Betta, Siamese Fighting Fish
  • Adult Size: 2.5-3 inches
  • Water Parameters: pH 6.5-7.5, Temperature 76-82°F

The Betta Fish — no aquarium species list would be complete without mentioning this vividly colored, flamboyantly finned showstopper. Plus, you know how I love my Bettas! With their flowing fins and a dazzling palette that spans from intense blues to fiery reds, Betta Fish serve as living sculptures that enrich your 20-gallon world with a stroke of underwater opulence.

Though often housed in cramped bowls in pet stores, Bettas flourish in more spacious environments, like your 20-gallon haven. Such room allows them to display a broader range of behaviors, from complex territorial dances to intricate nesting activities. But, ah, one caveat — Bettas are notoriously territorial. While they can cohabitate with other non-aggressive species, two male Bettas in the same tank are a recipe for underwater drama.

The care requirements for Betta Fish are straightforward, contributing to their status as one of the most accessible and rewarding species for fishkeepers of all experience levels. A filtered, heated tank and a balanced diet are all they need to express their vivacious personalities and stunning coloration fully.

The appeal of the Betta transcends its aesthetic virtues. It’s a fish with an attitude, a flair for the dramatic, and a presence that exudes charisma. Incorporating a Betta into your 20-gallon sanctuary elevates the environment from a collection of species to a dynamic landscape brimming with spectacle and nuance. It’s not merely about watching fish swim; it’s about being a spectator to an aquatic opera where the Betta often plays the lead role, compelling and complex.

4. Corydoras Catfish (Corydoras spp.)

cory catfish

  • Common Names: Cory Catfish, Corydoras
  • Adult Size: 1-3 inches, depending on species
  • Water Parameters: pH 6.0-7.8, Temperature 72-78°F

The Corydoras Catfish is a veritable vacuum cleaner of the aquatic realm, yet so much more than a mere janitorial addition to your 20-gallon aquatic microcosm. These small, armored catfish are, in fact, the epitome of underwater charm. While their somber coloration—ranging from ashen gray to dappled brown—may not stand out amidst a riot of tropical hues, their quirky behaviors and social interactions provide a captivating counterpoint.

Cory catfish have a knack for rooting through substrate, scavenging for food particles, yet displaying a degree of delicacy as they sift sand grains through their mouths. They add a functional aesthetic, creating fascinating patterns on the tank floor, almost like aquatic calligraphy. This industrious nature is beneficial for tank hygiene, but it’s also a source of endless fascination for those who take the time to observe.

Social creatures to their core, these schooling fish flourish in groups of five or more, exhibiting intriguing communal behaviors. They often synchronize their movements, rummaging through the substrate or ascending in a burst for a gulp of air—a quick, surprising dash that momentarily captures your attention and broadens your understanding of fish behavior.

Ease of care is another Corydoras selling point. They’re remarkably hardy and adaptable, making them ideal companions for various fish species. But remember, these creatures aren’t just functional; they’re charismatic, each movement a testament to the intricate ballet of interspecies dynamics.

5. Platy Fish (Xiphophorus maculatus)


  • Common Names: Platy, Moonfish, Southern Platyfish
  • Adult Size: 1.5-2.5 inches
  • Water Parameters: pH 6.8-8.0, Temperature 70-77°F

With their riot of colors and active demeanor, Platy Fish infuse a joyful exuberance into your 20-gallon underwater domain. A freshwater wonder, the Platy boasts a diversity of shades and patterns that seem plucked straight from an artist’s palette—fiery oranges, vivid yellows, and deep reds, sometimes stippled or streaked with complementary hues. The sheer visual feast they offer can almost make you overlook their affable nature and social versatility.

Why choose Platies for your aquarium? The list is long but let’s start with their gregarious disposition. They get along swimmingly with most other peaceful, community-oriented species, allowing for a harmonious blend of color and behavior within your aquatic canvas.

Another appealing trait is their resilience and adaptability. Platies thrive with minimal fuss, making them excellent candidates for both budding aquarists and veterans looking to add a splash of color with minimal commitment. Just ensure a diet rich in variety, and you’re set.

Their live-bearing reproductive habits offer another dimension to your fishkeeping journey. Witnessing the birth of new Platies, tiny replicas of their vivid parents, adds an awe-inspiring layer of complexity to your already vibrant setup. It’s one thing to maintain a fish tank; it’s another to cultivate a thriving, self-renewing micro-ecosystem.

6. Cherry Barb (Puntius titteya)

cherry barb

  • Common Names: Cherry Barb
  • Adult Size: 1.5-2 inches
  • Water Parameters: pH 6.0-8.0, Temperature 73-81°F

If you seek the artful blend of subtle beauty and dynamic energy, look no further than the Cherry Barb. This small, slender fish may appear unassuming at first glance, its base hue a muted silver. Yet, as you delve deeper into its nuances, you’ll discover bursts of vibrant red, especially prominent in males during mating season. It’s as though each Cherry Barb is a self-contained sunrise, gradually revealing its splendor as it acclimates to its surroundings.

But the Cherry Barb offers more than mere visual delight; it serves as an active yet peaceful component of your aquatic menagerie. This species of schooling fish thrives when kept with at least six of their kind, each individual adding a stroke of chromatic and behavioral complexity to your 20-gallon canvas. When you observe them darting in unison, flitting among aquatic plants and shoaling with striking precision, you’ll grasp the unique blend of serenity and vivacity they bring to your aquarium.

The Cherry Barb, despite its appealing aesthetics, is remarkably undemanding. They’re compatible with a wide range of water conditions and a diverse set of tank mates, as long as aggressive fish aren’t part of the equation. This adaptability makes them an asset in community tanks where multiple species must coexist in an intricate dance of underwater diplomacy.

7. Molly Fish (Poecilia sphenops)


  • Common Names: Molly, Short-finned Molly, Common Molly
  • Adult Size: 3-4 inches
  • Water Parameters: pH 7.5-8.5, Temperature 75-80°F

The Molly Fish is not just another pretty face in the underwater world, although its panoply of colors—ranging from dusky greys to luminescent golds — certainly makes it a striking addition. Within the confines of a 20-gallon tank, this species acts like a charismatic diplomat, effortlessly mingling with various other fish species and adding a convivial vibe to the environment.

Now, let’s talk personality. Mollies are an interactive lot. These fish are ceaselessly active, displaying a curiosity that leads them to explore every nook and cranny of your aquarium. This imbues your tank with a dynamic narrative, one filled with bouts of exploration, playful chases, and the occasional flair of showy swimming maneuvers. Ah, the dynamic Molly — a character in every sense!

Ease of care? Check. Mollies are impressively adaptable, accommodating a variety of water conditions. While they have a preference for harder, alkaline water, they are forgiving enough to tolerate less-than-ideal parameters for short periods, making them one of the more low-maintenance options for a mixed community setup.

Moreover, Mollies are livebearers, meaning that their reproductive cycles present an exciting subplot to the ongoing story within your fish tank. Witnessing the birth and growth of baby Mollies — miniatures of their colorful parents — adds a whole new dimension to your aquatic adventure.

8. Dwarf Gourami (Trichogaster lalius)

dwarf gourami

  • Common Names: Dwarf Gourami
  • Adult Size: 2-3.5 inches
  • Water Parameters: pH 6.0-7.5, Temperature 75-80°F

This one is a fish that evokes the serenity and mystery of an underwater Zen garden. With its complex pattern of alternating stripes and luminous hues — predominantly blues, oranges, and reds — the Dwarf Gourami can mesmerize even the most jaded observer. Its seemingly contemplative behavior and slow, elegant swimming style offer a soothing contrast to the ceaseless darting and dashing of many other fish species.

In the microcosm of a 20-gallon tank, the Dwarf Gourami embodies a unique equilibrium of beauty and tranquility. Unlike other more frenetic species, this fish seems to savor each moment, often pausing to explore plant leaves or nestle in secluded corners. Watching a Dwarf Gourami move through its aquatic realm is like watching the gentle unfolding of a well-crafted narrative, one that captivates through subtlety rather than spectacle.

Ease of care? Remarkably forgiving. Dwarf Gouramis are well-suited for aquarium newcomers, requiring only a stable, clean environment and a balanced diet to thrive. That said, they do appreciate well-planted fish tanks, which offer them hideouts and exploratory opportunities.

Ah, but the beauty of the Dwarf Gourami extends beyond its aesthetic and behavioral traits. These labyrinth fish possess a unique ability to breathe air, thanks to a specialized respiratory organ. This intriguing feature adds a layer of complexity to your tank, as you’ll occasionally witness them rise to the water’s surface for a quick gulp of air — a momentary breach that somehow feels like a whispered secret between you and the fish.

9. Zebra Danio (Danio rerio)

zebra danio fish with plants in background

  • Common Names: Zebra Danio, Zebrafish
  • Adult Size: 2-2.5 inches
  • Water Parameters: pH 6.5-8.2, Temperature 64-77°F

Behold the Zebra Danio — a streak of kinetic energy darting across your 20-gallon aquatic theatre. With their striking horizontal stripes, these nimble fish invoke a kind of underwater op art, simultaneously dynamic and entrancing. It’s not just their vivid appearance that captures the imagination; it’s their ceaseless movement, a perpetually animated state that livens up any aquatic setting.

The Zebra Danio’s rapid dashes and loops add not just visual but behavioral texture to your aquarium. Kept best in groups of six or more, they embody the essence of community living, often engaging in synchronized swimming that is nothing short of hypnotic. It’s like watching an unscripted ballet, a sequence of intricate maneuvers rendered all the more dramatic by their contrasting stripes.

Why consider Zebra Danios for your 20-gallon setup? First, they’re remarkably hardy, capable of adapting to a variety of water conditions. This adaptability, coupled with their high energy levels, makes them ideal companions for a diverse range of tank mates — provided those mates aren’t slow-moving or long-finned species that could be stressed or nipped at by the danios.

From a behavioral standpoint, these fish offer a continual spectacle of social interactions and swimming acrobatics. It’s not just “a fish swimming in water”; it’s a spirited choreography, an unfolding drama that captivates the eye and enriches the overall experience of fishkeeping.

Adding Zebra Danios to your 20-gallon aquarium is not merely a matter of populating space; it’s an investment in vivacity and intricate social dynamics. These little speedsters add depth and excitement to your underwater world, transforming an otherwise static environment into a pulsating vista of motion and color.

10. Harlequin Rasbora (Trigonostigma heteromorpha)

harlequin rasbora

  • Common Names: Harlequin Rasbora, Red Rasbora
  • Adult Size: 1.5-2 inches
  • Water Parameters: pH 6.0-7.5, Temperature 72-81°F

The Harlequin Rasbora, like a sliver of tropical twilight, carries within its small frame an arresting blend of subdued and vivid hues. Resembling a living watercolor, this fish sports a copper-orange body juxtaposed against a striking black ‘porkchop’ shape on its side. But the Harlequin Rasbora isn’t just a static tableau; its movements within a 20-gallon setting create an ever-changing kinetic display.

But, ah, don’t be beguiled by their appearance alone. These fish offer a depth of personality that lends a particular gravitas to your aquatic assembly. Their social nature means these schooling fish thrive when kept with six or more of their kind, and their fluid formations as they navigate the tank can be awe-inspiring. Here you see a dappled swirl of color; there, a fleeting, precise formation — each a tiny spectacle in this miniature ecosystem.

In terms of compatibility, Harlequin Rasboras could be considered the diplomats of the freshwater fish world. Known for being very peaceful fish, they harmonize well with a multitude of other small, non-aggressive species. They also display a unique ability to adapt to varied water parameters, provided those parameters remain relatively stable.

What marks this species as remarkable, though, is their subtly intricate behavior. Watch closely and you’ll discern courtship dances and territory explorations, each movement imbued with a complexity that belies their size. Adding Harlequin Rasboras to your setup isn’t merely an aesthetic choice; it’s a nod to the richness and diversity of aquatic life, an intricate ballet condensed into the confines of your 20-gallon fish tank.

11. Angelfish (Pterophyllum scalare)

angel fish

  • Common Names: Freshwater Angelfish, Common Angelfish
  • Adult Size: 6 inches (body height)
  • Water Parameters: pH 6.0-7.5, Temperature 75-82°F

There exists a sort of aquatic grandeur in the Angelfish, a species that transcends the stereotypical confines of freshwater fish expectations. With their majestic, fan-shaped fins and elegantly elongated bodies, Angelfish conjure the allure of the ocean’s most mystical creatures right in your 20-gallon tank—though, it must be said, a larger setup would better suit their grandiose demeanors as they mature.

On the behavioral front, Angelfish often exhibit personality traits akin to the ocean’s more prominent, imposing dwellers. They can be territorial, which adds a layer of complexity to their interactions with other fish. While relatively peaceful, these fish command their space with a royal air, circling their domains with a mixture of curiosity and caution.

Angelfish display a social structure that adds a cinematic element to their underwater world. They often form monogamous pairs, engaging in intricate courtship dances that culminate in the joint care of their eggs and fry. This ritualistic behavior—a nuanced ballet of movements and subtle communications—offers a mesmerizing focus for aquarists keen on breeding and observing familial dynamics.

Care requirements? Not for the faint of heart. Angelfish demand a certain standard of living: stable water parameters, a varied diet, and ample vertical swimming space to accommodate their lofty fins. Moreover, their penchant for staking out territories suggests the need for a well-designed aquatic landscape, rich in plants and hiding spots.

12. Swordtail Fish (Xiphophorus hellerii)


  • Common Names: Swordtail, Green Swordtail
  • Adult Size: 4-5 inches (males with extended tail fin)
  • Water Parameters: pH 7.0-8.4, Temperature 65-82°F

The Swordtail Fish is, without a shadow of doubt, a spectacle in finned elegance — almost like the swashbuckler of your aquarium world. Bearing a long, sword-like extension on its lower tail fin, the male Swordtail is designed to capture attention. Even beyond this visual flamboyance, there’s an innate vivacity to Swordtails, a blend of active swimming and exploratory gusto that adds liveliness to any 20-gallon tank.

Now, speaking of personalities, Swordtails display a communal demeanor that veers toward the peaceable end of the spectrum. Yet, don’t let their generally tranquil nature fool you. These fish can manifest fascinating social hierarchies, particularly among males. Ah, the dramas that unfold—a jostle for territory here, a quick tail-flashing dance there — all adding layers of behavioral nuance to your aquatic community.

When it comes to compatibility, Swordtails are akin to that well-liked guest at a dinner party who gets along with nearly everyone but appreciates some personal space. They cohabitate well with other peaceful species but are known to establish territories if too many similar-sized fish are present. So, a well-planned mix of species in your fish tank can result in a balanced, dynamic setting.

Swordtails are livebearers, offering aquarists the captivating chance to witness the cycles of birth and rearing. Imagine your 20-gallon microcosm enriched by the periodic arrival of fry, each a miniature replica of its vividly colored parent. With Swordtails, your tank becomes a living narrative of generational transition, a visual spectacle that’s continually refreshed and reborn.

13. Black Skirt Tetra (Gymnocorymbus ternetzi)

black skirt tetra Gymnocorymbus ternetzi

  • Common Names: Black Skirt Tetra, Black Widow Tetra
  • Adult Size: 2-3 inches
  • Water Parameters: pH 6.0-8.0, Temperature 70-85°F

The Black Skirt Tetra is not your run-of-the-mill aquarium resident; it’s an elegant enigma, a blending of stark contrasts and understated grace. With its dark vertical stripes running across a translucent body, this tetra evokes the ambience of a black-tie gala, adding a dash of solemn beauty to the typically vibrant palette of a 20-gallon freshwater tank.

Ah, but it’s not just about aesthetics. This species offers a unique combination of social fluidity and individual complexity. Black Skirt Tetras thrive in shoals, creating a mesmerizing symmetry as they move in unison. Yet, interspersed in this collective choreography are instances of individual flair, little detours from the group that exhibit a nuanced behavioral landscape.

These peaceful fish maintain a delicate balance when it comes to tank dynamics. On the one hand, their easy disposition makes them well-suited for a community setting. On the other hand, their occasional tendencies for nipping necessitate a careful selection of tankmates. Fast-moving species or those without long, flowy fins usually make the best companions.

Moreover, the Black Skirt Tetra’s care requirements sit comfortably in the moderate range, neither too demanding nor overly forgiving. This makes them an ideal candidate for hobbyists who are past the beginner stage and ready for a tad more complexity. Given proper care, including stable water conditions and a varied diet, these tetras show a resilience that prolongs their lifespan and intensifies their colors.

14. Kuhli Loach (Pangio kuhlii)

kuhli loach

  • Common Names: Kuhli Loach, Coolie Loach, Leopard Loach
  • Adult Size: 3-4 inches
  • Water Parameters: pH 5.5-7.0, Temperature 73-86°F

The Kuhli Loach is a species that offers an unconventional brand of intrigue. With its eel-like body and alternating bands of dark and light, this creature imparts an exotic, somewhat mysterious allure to any 20-gallon tank. By day, it hides beneath rocks and in crevices; come nightfall, it becomes a tireless investigator, weaving in and out of aquatic foliage, turning over substrate as if searching for hidden treasure.

But don’t mistake its reclusiveness for shyness. When grouped with its own kind — preferably in sets of at least three or four—Kuhli Loaches display an impressive range of social behaviors. You might witness a sequence where several loaches form what appears to be a wriggling mass, or a ‘Kuhli ball,’ as some aquarists affectionately call it. This fascinating spectacle adds not just a visual but also a behavioral texture to your aquarium.

Harmonizing well with other non-aggressive species, Kuhli Loaches bring to a community tank the advantage of being bottom-dwellers. They often share the lower levels of the tank with other peaceable species without causing territorial disputes. This trait also makes them useful in their role as substrate cleaners; these loaches enjoy sifting through sand and gravel in search of food remnants, indirectly contributing to the tank’s cleanliness.

The care requirements of Kuhli Loaches lean toward the moderate, demanding enough to excite the enthusiast but not so challenging as to discourage a diligent beginner. A well-planted tank with plenty of hiding spaces will see them at their best: active, curious, and ever the explorers.

15. Endler’s Livebearers (Poecilia wingei)

endler's livebearer

  • Common Names: Endler’s Livebearers, Endler’s Guppy
  • Adult Size: 0.8-1.4 inches
  • Water Parameters: pH 6.7-8.5, Temperature 75-81°F

The Endler’s Livebearer: a diminutive yet vivacious jewel that dances through your 20-gallon tank like stardust trailing a comet. At first glance, their small size may seem unremarkable; ah, but let your gaze linger. Soon you’ll find yourself ensnared by the males’ kaleidoscopic patterns and flashing colors, a mesmerizing blend of sapphire blues, emerald greens, and bursts of iridescent hues that defy easy categorization.

What sets these fish apart in a community tank is their remarkable sociability. If your tank were a bustling metropolis, Endler’s Livebearers would be its most amicable citizens, navigating the undersea avenues and byways with a carefree flair. These charmers do well in groups, their playful darting and chasing providing endless vignettes of underwater animation.

Let’s talk compatibility. Endler’s Livebearers are the peaceable sort, rarely showing aggression, even among themselves. They get along splendidly with other small, non-predatory species, making them ideal for a mixed-species, community setup. One fascinating quirk is their tendency to exhibit shoaling behavior when kept with similarly-sized fish, turning your aquarium into a living tapestry of color and motion.

Ah, but there’s more. Being livebearers, these fish offer the delightful possibility of aquarium-born offspring, adding both the joy of witnessing new life and a touch of natural population control. Carewise, they’re relatively undemanding, accepting a variety of foods and tolerating a wide range of water parameters—though, of course, stability is key.

In the grand tapestry of freshwater aquarium life, Endler’s Livebearers might be considered the whimsical brushstrokes that bring a composition to life. These radiant, sociable fish don’t just exist in your aquarium; they engage with it, creating dynamic interactions and captivating displays that elevate the entire aquatic experience.

16. Killifish (Aphyosemion spp., Fundulus spp., etc.)

clown killifish

  • Common Names: Killifish, Annual Killifish, Notho Killifish
  • Adult Size: 1-4 inches, depending on the species
  • Water Parameters: pH 6.0-7.5, Temperature 68-75°F (species dependent)

The Killifish is an aquatic enigma — visually arresting yet elusive, teeming with vibrant hues yet often hidden away in the most recondite corners of your tank. With a palette that rivals a painter’s dream, from vivid reds and blues to iridescent golds, these fish are the epitome of aquatic artistry.

Ah, but Killifish aren’t merely swimming canvases; they come equipped with individualistic personalities and exhibit a broad spectrum of behaviors. Some Killifish species are more retiring, preferring to lurk among aquatic plants or under driftwood. Others take on a more dynamic role, ever-moving and displaying assertive, albeit not aggressive, tendencies.

This temperamental range offers a palette of interactions for the astute aquarist. They can become the contemplative monks or the boisterous jesters of your aquatic realm, offering a welcome break from the predictable swimming patterns of other fish. Their general proclivity for upper-level swimming offers a vertical dimension to their interspecies relations, making them excellent choices for mixed-species tanks with bottom or middle-dwelling species.

Now, let’s discuss compatibility. Generally, Killifish can coexist with other peaceful species. However, due to their somewhat territorial nature and potential to eat smaller fish, picking the right roommates for them is crucial. Medium-sized, fast-moving fish often make the best tankmates.

Killifish are known for their fascinating breeding behaviors, involving unique rituals and, in the case of some species, the laying of eggs in damp substrates, akin to how they would behave in seasonal ponds in the wild. For the aquarist yearning for an intellectual challenge, breeding these fish can become an absorbing enterprise.

17. Bristlenose Pleco (Ancistrus spp.)

yellow bristle nose pleco

  • Common Names: Bristlenose Pleco, Bristlenose Catfish, Bushynose Catfish
  • Adult Size: 4-6 inches
  • Water Parameters: pH 6.5-7.5, Temperature 73-81°F

In the vast lexicon of aquarium species, the Bristlenose Pleco stands as the custodian extraordinaire—a diligent cleaner with a quirkiness that sets it apart. At first glance, the tendrils—those brush-like appendages sprouting from its snout—capture your attention. These aren’t merely ornamental; they serve as sensory organs that help the Pleco navigate and forage in dark or obscured conditions.

And, oh, how it forages! With an appetite for algae rivaling its keen sense of duty, the Bristlenose Pleco leaves glass, decor, and even plant leaves squeaky clean, although it’ll appreciate supplemental nourishment like algae wafers or fresh veggies. While many fish add beauty to a tank, the Bristlenose Pleco adds utility, serving as the janitor that every community aquarium needs. Yet, it goes about its duties with an idiosyncratic charm that elevates its status from mere worker to an engaging participant in your underwater ecosystem.

Compatibility? The Bristlenose Pleco is generally peaceable, cohabiting well with a range of community fish. However, owing to its somewhat territorial disposition—especially when it comes to choice hiding spots—it can show flashes of assertiveness. Best to give it its own little nook, away from other bottom-dwellers.

Another compelling feature of the Bristlenose Pleco is its relative ease of care. These fish are hardy, tolerating a range of water conditions so long as they remain stable. What they do require, however, is good water quality; a well-filtered tank and regular water changes are non-negotiables for these creatures.

18. Otocinclus Catfish (Otocinclus spp.)


  • Common Names: Oto, Dwarf Suckermouth, Otto Cats
  • Adult Size: 1-2 inches
  • Water Parameters: pH 6.0-7.5, Temperature 72-79°F

Imagine an unobtrusive sentinel — tiny but tenacious — that patrols your 20-gallon tank in ceaseless pursuit of its singular mission: algae elimination. Meet the Otocinclus Catfish, the under-the-radar algae eater virtuoso of aquarium maintenance. Though small in stature, this diminutive dynamo is a wonder of efficiency, voraciously cleaning algae off plants, glass, and decorations.

But wait! There’s a whole other layer to the Oto that tends to elude the casual observer. Despite their hardworking nature, these fish are innately peaceful and thrive best when in groups of at least three to six. When housed in social clusters, their interactions can become subtle performances, exhibiting collaborative scavenging and occasional synchronized swimming. Ah, they embody the best of both worlds: serenity and industry.

In terms of compatibility, Otos are your proverbial good neighbors—quiet, non-intrusive, and amicable. They pair excellently with a variety of small, peaceful fish and can even cohabit comfortably with more sizable but mild-mannered species. That said, their small size makes them susceptible to predation, so a community of equally peaceful species is the ideal setup.

Now, let’s talk maintenance. Otocinclus Catfish have particular water quality requirements; these are not fish for the neglected or irregularly cleaned tank. They demand well-oxygenated water and are particularly sensitive to nitrate levels. Regular water changes and an effective filtration system are your tickets to keeping these diminutive cleaners happy and active.

The Otocinclus offers a depth of character that belies its size. Though primarily sought for their housekeeping talents, these little catfish also bring a nuanced social dynamic and behavioral palette to any aquatic setting.

19. Clown Loach (Chromobotia macracanthus)

clown loach in fish tank

  • Common Names: Clown Loach, Tiger Botia
  • Adult Size: 8-12 inches (not suitable for long-term in a 20-gallon tank)
  • Water Parameters: pH 6.0-7.5, Temperature 75-85°F

Pause for a moment and envision a fish that not only arrests the eye but also piques the intellect and delights with its idiosyncrasies. The Clown Loach is an enduring favorite in the aquarium hobby, revered for its striking appearance and engaging behaviors. With its trademark orange body complemented by bold, ebony-black stripes, it’s a visual spectacle that serves as a buoyant counterpoint to the blues and greens commonly seen in aquatic landscapes.

But the Clown Loach is not merely an objet d’art. It’s a spirited participant in tank life, forging strong social bonds with its own kind. In a 20-gallon setting, it’s vital to acknowledge that young Clown Loaches can be housed temporarily, but as they grow, they’ll require a larger abode—ideally, at least 75 gallons. This is not a pet for the casual hobbyist but a long-term commitment requiring both space and attention.

Now, let’s ruminate on compatibility. While Clown Loaches are non-aggressive by nature, their penchant for social structures renders them best-suited for small groups. They are bottom dwellers, preferring the lower echelons of your tank. Their social antics—whether it’s play-fighting with their own kind or initiating a synchronized “loach dance”—add a compelling dimension to the underwater narrative unfolding in your aquarium.

In terms of care, these are hardy fish, amenable to a variety of water conditions within the specified parameters. However, they have a pronounced distaste for poor water quality and are susceptible to Ich, a common fish ailment. Therefore, meticulous attention to water quality is not a luxury but a mandate for Clown Loach ownership.

As a potential steward of a Clown Loach—or perhaps a small, youthful contingent—know that you’re not just acquiring a pet; you’re entering into a rewarding yet demanding relationship with an exceptionally social and remarkably intelligent creature.

20. Pearl Danio (Danio albolineatus)

celestial pearl danio

  • Common Names: Pearl Danio, Spotted Danio
  • Adult Size: 2-3 inches
  • Water Parameters: pH 6.0-8.0, Temperature 68-77°F

The Pearl Danio is a living brushstroke in the tapestry of your aquarium! Bedecked with luminescent specks that shimmer like pearls, these little jewels make a compelling argument for beauty in simplicity. Yet, let’s not mistake simplicity for monotony; these gems carry a flicker of vivacity that keeps them ever-engaging.

Their swimming patterns are akin to a choreographed dance—a bit of waltz, a dash of tango, all set against the backdrop of a watery stage. Whether it’s a brisk sprint along the length of the tank or a brief dalliance at the surface to nab a floating morsel, Pearl Danios never cease to entertain. No, they aren’t merely background dancers; they’re capable lead performers in the aquatic ballet of your tank.

When it comes to compatibility, Pearl Danios are as affable as they come. Their peaceful disposition makes them excellent candidates for community tanks, where they can harmonize with species of similar temperament. Moreover, their upper-level swimming habits provide a perfect complement to bottom-dwelling or mid-water species, creating a layered, dynamic environment.

However, bear in mind that these danios do have a penchant for social structures and are happiest in shoals of five or more. A solitary Pearl Danio is a forlorn sight, its incandescence dimmed by solitude.

21. Siamese Algae Eater (Crossocheilus oblongus)

siamese algae eater

  • Common Names: Siamese Algae Eater, SAE
  • Adult Size: 4-6 inches
  • Water Parameters: pH 6.5-8.0, Temperature 75-79°F

The unsung hero of the freshwater tank: the Siamese Algae Eater, a diligent worker with a penchant for tackling algae most fish turn their noses at. Yes, this fish is an ardent consumer of the notorious black beard algae — reason enough to consider it as a tenant in your 20-gallon aquatic abode. But don’t pigeonhole it as a mere custodian; the Siamese Algae Eater packs a punch in both personality and aesthetic appeal.

The Siamese Algae Eater’s elongated body, adorned with a single black stripe running from nose to tail, imbues it with a sense of dignified grace. Yet this fish is far from sedate; it’s an active swimmer, endlessly patrolling the tank, whiskers quivering as it scavenges for food. It oscillates between frenetic bursts of energy and slow, purposeful glides—a dance of exuberance and focus.

When it comes to compatibility, this Algae Eater is remarkably social and non-aggressive. It thrives in community settings, cohabiting well with a variety of peaceful fish. However, its ceaseless activity may unsettle more timid tankmates, so plan your community carefully. A well-chosen set of companions can amplify both the aesthetic and functional harmony of your aquarium.

On the care side, while the Siamese Algae Eater is relatively hardy, its quest for pristine living conditions is non-negotiable. Stable water parameters and a well-filtered environment are prerequisites for its well-being. That said, its algae-centric diet should be supplemented with high-quality sinking pellets and occasional vegetable matter.

22. Honey Gourami (Trichogaster chuna)

honey gourami

  • Common Names: Honey Gourami, Red Flame Gourami
  • Adult Size: 2-3 inches
  • Water Parameters: pH 6.0-7.5, Temperature 72-82°F

Enter the Honey Gourami, a petite yet impactful addition to your 20-gallon setup. With its warm, honey-colored hues and graceful demeanor, this fish is like a dash of sunlight in an aquatic landscape. But don’t let its demure appearance deceive you; the Honey Gourami offers a blend of personality traits that make it a complex and entertaining inhabitant.

In terms of behavior, Honey Gouramis are intrinsically peaceful, but exhibit a compelling range of emotions. Whether constructing intricate bubble nests during breeding or showing slight color variations to indicate mood, these fish are emotive artists, painting their feelings in living watercolor. Given their capacity for nuanced expression, it’s no wonder they’re adored by aquarists seeking depth of character in their finned companions.

When contemplating tankmates, you’ll find that Honey Gouramis are exceptionally agreeable, coexisting well with most peaceful species. Because they are predominantly surface dwellers and enjoy meandering through the upper reaches of the tank, they complement bottom-feeding or mid-water species excellently, creating a balanced, tiered environment.

As for care requirements, Honey Gouramis are relatively undemanding but benefit from well-planted fish tanks that offer shelter and visual intrigue. They’re amenable to a variety of water conditions within their comfort range and thrive on a diet that includes both plant-based foods and protein.

23. Pictus Catfish (Pimelodus pictus)

pair of pictus catfish in the bottom aquarium

  • Common Names: Pictus Catfish, Angel Catfish, Spotted Pim
  • Adult Size: 4-6 inches
  • Water Parameters: pH 6.5-7.5, Temperature 75-81°F

Consider the Pictus Catfish, a mesmerizing enigma swathed in a constellation of spots, its long, flowing barbels probing the watery depths like sinuous antennas. Strikingly adorned yet elusive, this fascinating creature is truly a paradox, offering a blend of eye-catching beauty and cryptic behavior that few other species can match.

The Pictus Catfish navigates the lower strata of the tank, its barbels in constant contact with the substrate, rooting out morsels of food and savoring the tactile sensations of its environment. Yet, intermittently, it bursts forth in a rapid ascent or lateral dash—seemingly spontaneous acts that punctuate its otherwise slow, deliberate movements. This blend of stately grace and unpredictable vivacity lends a compelling dynamism to its behavior, transforming the tank’s lower regions into a theater of intrigue.

As for its compatibility, the Pictus is a social creature that values the company of its own kind, although its predilection for smaller tankmates as potential snacks warrants caution. Indeed, it thrives best in a community of larger, more robust species, given its propensity for nocturnal prowling and the occasional burst of speed that can startle more timid neighbors.

With respect to care, the Pictus Catfish is relatively hardy but unforgiving of neglect. It insists on clean, well-oxygenated water and a diet rich in protein, making high-quality sinking pellets and occasional servings of live or frozen foods essential.

Factors to Consider When Choosing Fish for a 20-Gallon Tank

So, you’ve got a 20-gallon tank — excellent! It’s an ideal size for newcomers and veteran aquarists alike, offering a sweet spot between manageability and diversity. But before you rush out to stock it with a variety of finned residents, hold your seahorses! There are factors — vital ones — that demand scrutiny to ensure that your aquatic sanctuary flourishes. What follows is a dissection of these considerations, each one nuanced and interlinked with the others.

Size and Growth Potential

One mustn’t underestimate the room that fish need to move, grow, and engage in natural behaviors. Always check the adult size of the fish and aim for species that won’t outgrow your setup.

Social Structure

Fish can be sociable, aggressive, shy, or even indifferent to their tankmates. Know the temperaments of your chosen species and how they interact. Some fish need to school; others prefer solitary corners.


Fish compatibility is the linchpin of a harmonious tank. Some species mix well; others clash. Carefully research whether your chosen fish will get along, based on their respective temperaments, dietary needs, and territorial behaviors. It’s a bit like matchmaking but for fish!

Water Parameters

You’ve got to know your pH from your KH. Every fish species has an optimal range of water conditions—temperature, hardness, acidity — that mimic its natural habitat. Strive for a community that shares similar water requirements.

Activity Levels

Different fish occupy different layers of the tank—top, middle, and bottom. Strategically choose species that will utilize different spaces without crowding each other. A fish that roams the bottom can peacefully coexist with a mid-layer swimmer and a surface dweller.

Dietary Needs

All fish must eat, but not all fish eat the same things. Carnivores, herbivores, and omnivores require different types of food. Some may require specialized diets, while others are less finicky.

Aesthetic Harmony

Your aquarium is a visual entity. Colors, shapes, and movement patterns can either clash or harmonize. While it may seem superficial, the visual aspect is an integral part of the aquarium experience for many enthusiasts.

Maintenance and Care Level

Some fish are hardy and forgiving; others are sensitive and demand precise care. Assess your willingness and ability to meet these needs, especially if you’re inclined toward more delicate or specialized species.

Suggested Fish Combinations for a 20-Gallon Tank

Assembling the right community of freshwater fish for your 20-gallon aquarium can feel a bit like curating an art exhibit. Each species brings its own palette of colors, its own unique behavioral patterns, and, indeed, its own needs and preferences. But when orchestrated with finesse, the outcome is a living, breathing masterpiece—a vibrant, balanced ecosystem where each inhabitant thrives.

And it’s not merely a question of who to include; it’s also a matter of how many. To make this intricate calculus a touch easier, let’s delve into some thoughtfully devised combinations, complete with recommended quantities.

The Peaceful Retreat

  • Core Fish: Neon Tetras (8-10), Corydoras Catfish (4-5)
  • Additional Inhabitants: Honey Gourami (2), Otocinclus Catfish (3)
  • Why it Works: This serene assembly radiates visual splendor while maintaining a tranquil vibe. The Neon Tetras offer iridescent beauty, the Corydoras engage in endearing bottom-feeding, the Honey Gouramis add a layer of gentle personality, and the Otocinclus act as algae eradicators.

The Social Mixer

  • Core Fish: Cherry Barbs (6-8), Harlequin Rasboras (6-8)
  • Additional Inhabitants: Dwarf Gourami (1-2), Siamese Algae Eater (2)
  • Why it Works: Cherry Barbs and Harlequin Rasboras flourish in groups, leading to synchronized swimming that’s hypnotically beautiful. A Dwarf Gourami or two inject sophisticated charm, while Siamese Algae Eaters contribute both utility and kinetic energy.

The Nautical Novelette

  • Core Fish: Zebra Danios (6), Black Skirt Tetra (4)
  • Additional Inhabitants: Bristlenose Pleco (1), Endler’s Livebearers (4-5)
  • Why it Works: Zebra Danios zip around with restless vigor, contrasting the more stately Black Skirt Tetras. The Bristlenose Pleco undertakes cleanup duty, and the Endler’s Livebearers ornament the tank with their dazzling hues.

The Complexity Quartet

  • Core Fish: Pictus Catfish (2-3), Angelfish (2)
  • Additional Inhabitants: Kuhli Loach (3-4), Pearl Danio (5-6)
  • Why it Works: Angelfish add a regal presence, while Pictus Catfish keep viewers on their toes with their unpredictable antics. The Kuhli Loach brings a playful, wiggly dynamic, and the Pearl Danios round out the ensemble with their scintillating group choreography.

Calculating the right number of each species allows for an environment where social fish can school, loners can find solitude, and everyone has enough room to live their best fishy life. Consider these suggestions as starting points and feel free to riff on these combinations, tailoring your tank’s community to your specific vision and conditions.


How Often Should I Clean My 20-Gallon Aquarium?

A regular cleaning schedule is vital for maintaining a healthy environment. Perform partial water changes of about 10-20% every week or two. Vacuum the substrate and clean the tank walls at least once a month.

How Do I Cycle a New 20-Gallon Tank?

Cycling a new tank involves establishing beneficial bacteria to break down waste products. This usually takes between 4-6 weeks. Use a water testing kit to monitor levels of ammonia, nitrites, and nitrates to know when the tank is ready for fish.

Can I Keep Plants in My 20-Gallon Tank?

Absolutely! Plants not only enhance the aesthetic appeal of your tank but also provide hiding spots and help improve water quality. Species like Java Fern, Anubias, and Amazon Sword are excellent choices.

Can I Mix Different Species of Fish?

Yes, you can mix different species, but this requires careful planning to ensure compatibility. Factors such as temperament, size, and dietary needs must be considered to create a harmonious environment.

What Should I Do if My Fish Get Sick?

Isolate the sick fish in a separate quarantine tank if possible. Identify the symptoms and consult with a veterinarian or a reliable fish care guide for treatment options. Make necessary changes in the main tank to prevent the spread of illness.

How Many Fish Can I Keep in a 20-Gallon Tank?

The number of fish depends on the species. A general rule of thumb is one inch of fish per gallon of water, but this is overly simplistic. Consider factors like activity level, growth potential, and territorial needs for a more accurate count.

20 Gallons is a Great Tank Size to Work With

The 20-gallon aquarium stands as a veritable microcosm of life, offering a sanctuary of serenity and endless opportunities for learning. It’s not just about the fish; it’s about curating an ecosystem, a living tableau that enriches your space and spirit.

As you embark on this aquatic journey, remember that the keys to a thriving tank are planning, knowledge, and a touch of creativity. Success in fishkeeping doesn’t come overnight; it’s a continual process of learning, adapting, and marveling at the mysteries of underwater life.

So, dive in—your aquatic utopia awaits. Whether you’re a neophyte or a seasoned aquarist, the quest for the perfect 20-gallon setup is a rewarding adventure. Happy fishkeeping!

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