Harlequin Rasbora in an aquarium. Photo: dinomariobob. View source · CC0 1.0 · 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 reviewed
What the human review covered
Fish-selection text and identity notes reviewed by Simon.
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.
Harlequin Rasbora
Trigonostigma heteromorpha
Reference photo: dinomariobob. View original · CC0 1.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.
What to notice
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.
Electric Blue Acara
Electric-blue aquarium form; ancestry not established
Reference photo: dinomariobob. View original · CC0 1.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.
What to notice
Confirm the electric-blue aquarium form. This guide does not assert a specific hybrid pedigree or pure-species ancestry from appearance alone.
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.
Siamese Algae Eater
Crossocheilus oblongus
Several Crossocheilus species are traded under similar algae-eater names. Confirm the exact species; a black stripe by itself is insufficient.
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.
Diamond Tetra
Moenkhausia pittieri
Reference photo: Igor Balashov. View original · CC BY 4.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.
What to notice
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.
American Flagfish
Jordanella floridae
Reference photo: Duarte Frade. View original · CC BY 4.0. Provider large rendition (maximum 1024px); no subsequent cropping or colour changes.
What to notice
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.
Amazon Puffer
Colomesus asellus
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.
Head-and-tail Light Tetra
Hemigrammus ocellifer
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.
Blue Dolphin Cichlid
Cyrtocara moorii
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.
Silvertip Tetra
Hasemania nana
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.
Flying Fox
Epalzeorhynchos kalopterum
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.
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.
Supports checking adult needs, body condition, breathing, behavior, and the wider sales system, while recognizing that a normal-looking fish may still carry disease.
Flying fox scientific name. No source here establishes electric-blue acara pedigree.
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.
TankWiseFreshwater aquarium companion
Check the fish. Then check the fit.
TankWise screens what your fish needs first, then compares against your aquarium, water, and current livestock before you buy.
Harlequin RasboraTrigonostigma heteromorpha
Electric Blue AcaraElectric-blue aquarium form; ancestry not establishedSiamese Algae EaterCrossocheilus oblongus
Diamond TetraMoenkhausia pittieri
American FlagfishJordanella floridaeAmazon PufferColomesus asellusHead-and-tail Light TetraHemigrammus ocelliferBlue Dolphin CichlidCyrtocara mooriiSilvertip TetraHasemania nanaFlying FoxEpalzeorhynchos kalopterum