Which fish for your first aquarium

Your first fish decide 80% of whether the hobby sticks or you quit after two months. Badly picked fish generate problems no fertiliser calculator can fix — they die, they fight, they don't grow, or they outgrow the tank.

This guide walks you through 5 selection rules, the 7 best species for beginners, a "don't start with this" list, sample stockings for 54 L / 100 L / 200 L, and compatibility rules. Ends with real-life FAQ.

Prerequisite: the tank must be cycled before the first fish. If you don't know what that means, start with our nitrogen cycle guide.

1. Five rules for picking your first fish

Rule 1. Your tap water > your dream species

The easiest tank is one whose parameters match your tap. Hard water (GH 15+, pH 7.5+) — forget discus. Soft tap (GH 4, pH 6.8) — neons and Amazon fish are perfect, African cichlids are out.

Test your tap (GH/KH/pH) before picking stock. More in our water parameters guide.

Rule 2. Fish size vs tank size — "1 cm per 1 L" is a myth

The old "1 cm of fish per 1 L of water" rule oversimplifies. In practice what matters:

• Adult size (not current — fish usually grow 2–3×).
• Swimming space — a betta needs little, a goldfish a lot.
• Filter capacity (3–5× tank volume per hour).
• Activity level — shoaling fish need horizontal space, even if small.

Practical rule: for 54 L — max 12–15 small fish (under 5 cm). For 100 L — ~25 small or 10 medium. For 200 L — plenty of room to plan.

Rule 3. Temperament — peaceful, semi-aggressive, aggressive

Fish have personalities. For starters stick to peaceful community species — fewer fights, less nipping, fewer deaths. Classic mistake: adding a tiger barb to a neon tank (it nips their fins).

Rule 4. Shoaling fish must be in shoals

Neons, white clouds, corydoras, otocinclus, rasbora — all shoaling species that stress alone. Minimum 6 (ideally 8+). Three neons are three stressed, colourless, disease-prone fish — not a shoal.

Rule 5. Tank zones — top / middle / bottom

A good stocking fills the whole tank rather than clumping in one layer. Simplified zones:

• Top: guppies, betta, labyrinth fish (gourami), livebearers.
• Middle: neons, white clouds, rasbora, barbs, angelfish.
• Bottom: corydoras, plecos, otocinclus, algae eaters.

2. Seven species perfect for starters

Neon tetras (Paracheirodon innesi)

• Why: the classic. Colourful, peaceful, forgiving. A gorgeous shoal in any tank.
• Tank: from 54 L.
• Shoal: min. 8 (ideal 10–12).
• Parameters: pH 6.0–7.0; GH 2–8; temp 22–26 °C.
• Note: sensitive to unstable parameters — mature tank.

White cloud minnows (Tanichthys albonubes)

• Why: the easiest aquarium fish. Tolerate a wide range of parameters, cooler water, beginner mistakes.
• Tank: from 54 L.
• Shoal: min. 6.
• Parameters: pH 6.5–8; GH 5–20; temp 18–24 °C.
• Note: don't like warm water (> 26 °C).

Guppies (Poecilia reticulata)

• Why: dramatic colours, livebearing (you'll quickly see fry), tolerate hard water.
• Tank: from 54 L.
• Shoal: min. 1 male + 2 females (a lone male harasses a single female to death).
• Parameters: pH 7.0–8.0; GH 8–20; temp 22–26 °C.
• Note: breed fast — in 100 L you can have 50 guppies in a year.

Platies (Xiphophorus maculatus)

• Why: calmer than swordtails, equally colourful, hardy. Livebearers.
• Tank: from 80 L.
• Shoal: 2–4 (prefer females — less bullying).
• Parameters: pH 7.0–8.0; GH 8–18; temp 22–26 °C.

Bronze corydoras (Corydoras aeneus)

• Why: classic bottom dwellers, scavenge leftover food, fun to watch, very peaceful.
• Tank: from 80 L (100 L recommended).
• Shoal: min. 6 (shoaling!).
• Parameters: pH 6.5–7.5; GH 4–12; temp 22–26 °C.
• Note: need soft substrate (sand) or rounded gravel — sharp-edged gravel cuts their barbels.

Betta splendens — solo

• Why: one fish, big personality, beautiful fins. Ideal for a 30–40 L tank.
• Tank: from 30 L (not a 5 L bowl).
• Stocking: one male, optionally with a few Amano shrimp.
• Parameters: pH 6.5–7.5; GH 5–15; temp 24–28 °C.
• Note: never with other male bettas. Not with guppies (the betta shreds their fins). Not with barbs.

Harlequin rasbora (Trigonostigma heteromorpha)

• Why: beautiful shoal, peaceful, a bit hardier than neons.
• Tank: from 80 L.
• Shoal: min. 8.
• Parameters: pH 6.0–7.5; GH 2–10; temp 24–28 °C.

3. What to avoid starting out

Discus (Symphysodon)

Needs 200+ L, stable parameters, 28–30 °C, daily or weekly 30–50% changes. Gets sick at the slightest stress. Price: $20–100 per fish. Not for starters.

Full-fin angelfish (Pterophyllum scalare)

Needs min. 150 L (tall), aggressive when breeding. Eats neon shoals. Grows to 15+ cm.

Piranhas

Need huge tanks (300+ L), dangerous to handle, not a community fish.

Oscar (Astronotus ocellatus)

Grows to 30+ cm. Needs 400+ L. Eats small fish.

Chinese algae eater (Gyrinocheilus aymonieri)

Deceptively innocent in the shop. As an adult (20+ cm) aggressive, attacks other fish, stops eating algae. Often confused with the Siamese algae eater (SAE) — the real algae eater.

Goldfish (Carassius auratus)

Cold-water (18–22 °C) — incompatible with any tropicals. Needs 100+ L for 2 fish (very messy). Never put into a warm tropical tank.

Tiger barb (Puntigrus tetrazona)

Beautiful colours and lively, but nip the fins of peaceful fish (neons, guppies, bettas). Only with other barbs or robust fish (e.g. five-banded barb).

4. Sample stockings

54 L tank (60×30×30 cm)

The smallest sensible tank for a beginner. Limits species choice. Options:

• "Classic": 8 neons + 5 bronze corys + 1 dwarf ancistrus.
• "Betta": 1 betta + 5 Amano shrimp + 3 otocinclus.
• "Livebearer": 1 male + 3 female guppies + 5 panda corys + 5 white clouds.

100 L tank (80×35×35 cm)

The sweet spot for a beginner. More options, more stability:

• "Amazon": 12 neons + 8 white clouds + 6 bronze corys + 1 ancistrus.
• "Asian": 10 harlequin rasbora + 8 white clouds + 5 corys + 1 dwarf gourami.
• "Colourful": 3 platies + 2 swordtails + 8 neons + 5 bronze corys.

200 L tank (120×40×40 cm)

Freedom. You can mix larger groups, add "flagship" species.

• "Big shoal": 20 neons + 10 white clouds + 8 corys + 2 ancistrus + 6 otocinclus.
• "Angelfish + community": 4 angels + 15 neons + 8 corys + 1 ancistrus. (Note: once angels mature, small neons may be eaten.)
• "Dwarf cichlids": an apistogramma pair + 15 neons + 10 white clouds + 8 corys.

5. Compatibility — what goes with what

Universal rule: similar parameter needs + similar temperament + different tank zones = a good mix.

6. Order of introduction — not all at once

Even with the cycle complete, a sudden 20-fish drop overloads the filter and triggers a mini-cycle with an ammonia spike. Spread the stocking over 3–5 weeks:

1. Week 1–2: 25–35% of target stocking. Ideally 5–7 of the hardiest fish (white clouds, guppies).
2. Week 3: another 25–35%. Corys, platies, rasbora.
3. Week 4–5: the rest, more delicate species (otocinclus, neons, gouramis).
4. Between batches:test NH₃ and NO₂⁻. If > 0, wait another week.

7. Where and how to buy

Where

• Local aquarium shops with active rotation — fish don't sit for weeks in dirty water. Ask when the last delivery was.
• Private breeders (Facebook groups, forums, aquarium shows) — better prices, healthier fish, often better genetic lines. Add a week of acclimation to the buying timeline.
• Large chain aquarium stores — OK for standard species, watch out for fish in transit.

What to look for in the shop

• Activity: fish should swim normally, react to movement. Huddling in a corner = sick.
• Colours: vibrant and sharp. Pale, washed-out fish = stress or early illness.
• Fins: intact, no shreds, no white coating.
• Body: no white spots (ich), no ulcers, no "sunken belly" (starvation) or abnormally bloated (dropsy).
• Gills: breathing regularly, not "gasping" at the surface.
• Other fish in the tank: if the same tank has a visibly sick or a few dead fish — don't buy anything from that tank.

What to avoid

• Fish on "clearance" or heavy discount — usually for a reason.
• Shops where tanks are algae-covered, water is cloudy, equipment is neglected.
• Salespeople who discourage water testing or say "you can just drop them in".

8. Acclimation — first 48 hours

On the way from the shop

• Temperature on the trip shouldn't drop below 20 °C in winter (insulated bag).
• Don't leave the bag in sun in summer — overheating kills.
• Transport time max 2 hours.

At home

1. Temperature: float the sealed bag in the tank for 15–20 min. Water equalises.
2. Parameters: every 5 min add a teaspoon of tank water to the bag for ~30 min (drip method). Shop water may have different pH, GH, TDS.
3. Transfer: net the fish, discard shop water in the sink, fish into the tank. Shop water may contain medications, pathogens, excess ammonia.
4. After: dim the lights for 2–3 h. New fish are stressed; bright light makes it worse.

First 48 hours

• Don't feed for the first 24 h. Fish is adjusting.
• Watch: activity, behaviour, no aggression from existing residents.
• After 24 h — small feeding. If not eating, wait another 24 h.
• If after 48 h still not eating or swimming normally — you have a problem. Check parameters, observe.

9. FAQ

Will guppies overflow my tank?

Yes, if you drop in a mix of males and females. A female produces 20–60 fry every 4–6 weeks. In 100 L after a year you can have 50+ guppies. Solutions: (1) males only, (2) move fry to a separate tank, (3) fish that eat fry (angels, bettas, apistogramma) — though that's cruel pragmatism.

I bought 3 neons instead of 8. Now what?

Add the rest as soon as possible. Three neons stress, go pale, get sick easier. The tank can handle another 5 neons (another batch, a week apart). Meanwhile neons can be calmer in the company of similar species (white clouds, rasbora).

Can I keep fish and shrimp together?

Most fish eat small shrimp (Neocaridina). With Amano shrimp (3–5 cm) most fish are fine. Angels, gouramis, larger tetras will eat even Amanos. Safest: betta + Amano shrimp, or a shrimp-only tank.

I bought a sick fish. What do I do?

Immediately to a separate "quarantine" tank (can be a 20 L plastic tub with filter and heater). Observe for 2–4 weeks, treat per symptoms. Never add a sick fish to the main tank — it'll infect the rest.

Can a betta live with guppies?

No, no, and no again. A betta sees long colourful fins on a guppy as a threat (it thinks it's another betta). Result: nipped guppies, torn fins, possibly a dead guppy. A betta should be solo or with monochromatic, short-finned tank mates (corys, otocinclus, shrimp).

How long does a shop-bought fish need to settle in?

Temperature — 20 min. Water parameters — 30 min (drip method). Full behavioural acclimation and immunity recovery — 1–2 weeks. During this time the fish is more disease-prone, so good parameters and calm matter.

How long should I watch the tank after adding fish?

First hour — intensely. First 48 hours — multiple checks a day. First week — daily NH₃ and NO₂⁻ tests (is the filter keeping up?). Then back to standard routine.

Can I add fish to a tank with green water / bloom?

No. Cloudy water means parameters aren't stable. Clear the water first (see our cloudy water guide), then fish.

Wrap-up

The first fish are the most important aesthetic-functional decision in your tank. Good choices make the hobby a joy; bad ones, a frustration. Stick to 3 core rules:

1. Match fish to your water, not to the Instagram photo you fell in love with.
2. Buy shoaling fish in shoals (8+), not three at a time.
3. Spread stocking over 3–5 weeks, not one weekend.

For a typical 54 L: 8 neons + 5 bronze corys + 1 ancistrus is a classic that works. For 100 L you have freedom — add a dwarf gourami, a mix of white clouds, anything that fits the temperament. The rest is time and observation.

Once the first stocking stabilises, see our water change frequency guide — the routine is what keeps fish alive for years.