Freshwater Fish Species Profiles

Last updated: November 2026

Most fish emergencies trace back to a species-husbandry mismatch: a betta in an unheated bowl, a goldfish in ten gallons, a lone tetra school. Each profile below gives the honest minimums — tank size, water parameters, temperament — and the illnesses that species actually gets, linked to the symptom guides.

Betta

Heated 5+ gal, labyrinth breeder, fin rot & ich watch.

Goldfish

Cold water, huge waste output, swim bladder prone.

Neon tetra

Schools of 6+, soft acidic water, neon tetra disease.

Guppy

Hardy livebearer, ich and flukes after temperature dips.

Angelfish

Tall tanks 29+ gal, warm and picky about tankmates.

Corydoras

Armored bottom-schooler, smooth substrate, barbel health.

Before you buy any fish

Match the tank to the species at adult size, not pet-shop size. Check the numbers in each profile or run the stocking calculator.
Cycle the tank first (fishless cycling takes 4–6 weeks; ammonia 0 / nitrite 0 / nitrate rising is the green light). Grab the checklist from the symptom finder page.
Quarantine new arrivals 2–4 weeks in a separate tank — it's the single best disease insurance in the hobby.
Buy from shops whose display tanks look clean; a cloudy display tank is a diagnosis on its own.

Severe cases: consult an aquatic-experienced vet where available.