How to Choose Healthy Oscar, Serpae Tetra & 8 More Aquarium Fish

Fish assessed

Oscar · Serpae Tetra · Red-tail Shark · Gold Barb · Thick-lipped Gourami · Giant Gourami · Coral-red Pencilfish · Lemon Cichlid · Bucktooth Tetra · Nicaraguan Cichlid

A store-side guide to Oscar, Serpae Tetra and eight more freshwater fish: body condition, warning signs and identity checks.

By Simply Submerged AquaticsOctober 17, 202616 min readReviewed by SimonAI-generated draft disclosure

Serpae Tetra in an aquarium. Photo: Diogo Luiz. View source · CC BY 4.0 · Provider large rendition (maximum 1024px); no subsequent cropping or colour changes..

Use the guide at the retailer to compare breathing, posture, body condition, skin, fins, eyes, and behavior with what is normal for the species. Look at the whole sales system, ask about feeding and recent arrivals, and quarantine every new fish before it shares water or equipment with an established aquarium.

This is an observation guide, not a diagnosis. A fish that looks healthy can still carry pathogens, while transport, lighting, age, sex, and social position can change normal appearance and behavior.

Photographs are reference examples, not evidence that an individual fish is healthy. Profiles without a verified aquarium photograph remain text-only.

Content transparency

AI-generated draft, human-reviewed publication

This guide was drafted with generative AI used to organize research and prepare an initial version. The AI output was not treated as an authority or source. Simon from the Simply Submerged Aquatics team reviewed the published guide for accuracy and completeness within the scope recorded below.

Human reviewerSimonTankWise product lead and freshwater aquarist

Last reviewedOctober 17, 2026

What the human review covered

Fish-selection text and identity notes reviewed by Simon.

Meet the team and read the editorial review process

Key takeaways

Watch the complete sales tank before choosing an individual fish.
Compare breathing, posture, body condition, skin, eyes, fins, and response rather than relying on one sign.
Allow for normal species behavior, including resting, hiding, schooling, feeding patterns, territorial display, and social position.
Confirm the scientific identity and eventual aquarium needs before buying.
A healthy-looking fish still needs a suitable aquarium; compare it with your saved tank in TankWise before buying.

Store-side field guide

10 fish at a glance

Match the store label to the fish, then jump straight to its healthy and warning signs.

OscarAstronotus ocellatus

Serpae TetraHyphessobrycon equesRed-tail SharkEpalzeorhynchos bicolor

Gold BarbBarbodes semifasciolatus

Thick-lipped GouramiTrichogaster labiosa

Giant GouramiOsphronemus goramyCoral-red PencilfishNannostomus mortenthaleri

Lemon CichlidNeolamprologus leleupiBucktooth TetraExodon paradoxusNicaraguan CichlidHypsophrys nicaraguensis

Check the sales tank before the fish

Watch before anyone taps the glass, feeds the fish, or reaches for a net. Compare breathing, posture, body condition, skin, fins, eyes, and behavior across the group rather than choosing only by color or activity.

Pause if a tankmate is dead, unable to balance, extremely thin, ulcerated, heavily spotted, covered in growth, or breathing with pronounced effort. Ask when the fish arrived, whether it has eaten, and whether nearby tanks share filtration.

A feeding response is useful evidence, but it does not prove that a fish is disease-free. Quarantine every new arrival separately and avoid sharing wet equipment with the established aquarium.

Observe the group from a distance before selecting a candidate.
Compare the candidate with several fish of the same species when possible.
Confirm the store label and scientific identity.
Ask about arrival date, feeding, treatment history, and shared filtration.
Check the species against your aquarium in TankWise before purchase.

Oscar

Astronotus ocellatus

Compare this fish with several of the same species when possible. Ask the retailer about feeding, arrival time and the behavior you observe. Brief hiding or a social display is different from persistent exclusion, injury or inability to feed; interpret it alongside breathing, body condition and the whole sales tank.

Serpae Tetra

Hyphessobrycon eques

Reference photo: Diogo Luiz. View original · CC BY 4.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.

What to notice

Red-tail Shark

Epalzeorhynchos bicolor

Gold Barb

Barbodes semifasciolatus

Reference photo: Michel Langeveld. View original · CC BY 4.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.

What to notice

Thick-lipped Gourami

Trichogaster labiosa

Reference photo: Daniel Schelesky. View original · CC BY 4.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.

What to notice

Giant Gourami

Osphronemus goramy

Reference photo: Matthew Inabinett. View original · CC BY 4.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.

What to notice

Coral-red Pencilfish

Nannostomus mortenthaleri

Lemon Cichlid

Neolamprologus leleupi

Reference photo: Matthew Inabinett. View original · CC BY 4.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.

What to notice

Bucktooth Tetra

Exodon paradoxus

Nicaraguan Cichlid

Hypsophrys nicaraguensis

Sources and further reading

These references provide scientific or technical background and disclose how TankWise works. External references do not imply that every current TankWise catalog value was sourced from, or reviewed by, those organizations. See the checker methodology and known limits for that distinction.

Selection of FishMerck Veterinary Manual
Veterinary-reviewed guidance on assessing a fish, its environment, skin, fins, eyes, movement, and alertness before purchase.
Selecting a FishAmerican Veterinary Medical Association
Supports checking adult needs, body condition, breathing, behavior, and the wider sales system, while recognizing that a normal-looking fish may still carry disease.
Pet Fish HealthRSPCA
Species-aware health context for appetite, breathing, alertness, eyes, fins, scales, and swimming.
FishBase Species SearchFishBase
Scientific identity, distribution, biology, size, and cited species information used alongside other qualified sources.
TankWise checker methodology and known limitsSimply Submerged Aquatics
The inputs, rules, safety limits, and uncertainty boundaries behind the TankWise aquarium comparison.

Frequently asked questions

Can a fish that looks healthy still carry disease?

Yes. Visual screening can identify reasons to pause, but it cannot prove that a fish is free of pathogens or parasites. Quarantine new arrivals and avoid sharing wet equipment with an established aquarium.

Should I buy from a tank containing a dead or visibly distressed fish?

Pause and ask what happened, whether the tanks share filtration, and what action the retailer is taking. Choosing another fish from the same water does not remove shared exposure.

Is unusual color, hiding, or resting always a sign of illness?

No. Lighting, transport, age, sex, social position, and species-normal behavior can change appearance and activity. Review breathing, posture, body condition, skin, fins, eyes, and the condition of the whole tank together.

Where does TankWise fit?

This guide helps screen the individual fish. TankWise then compares the species' needs with your aquarium, water, and current livestock. It does not diagnose illness or guarantee compatibility.

AI-generated draft, human-reviewed publication

What the human review covered

Key takeaways

10 fish at a glance

Sources and further reading

Frequently asked questions

Check the fish. Then check the fit.

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