How many fish can a 60cm tank hold?

There is no useful number of fish per centimetre of tank length, because the limit is set by water volume. A 60 by 40 by 40cm tank holds roughly 75 litres internally, or about 65 litres once substrate and rock are displaced: that is ample for six 4cm tetras, and already too little for one oscar that reaches 30cm. Work in that order, size the tank for the largest adult first and then count the fish that fit the remaining volume.

Why keep peaceful fish away from aggressive ones?

Because a tank is a closed space and the fish being chased has nowhere to go. An aggressive fish keeps driving its tank mate off and nipping its fins, and the peaceful fish spends its time behind the filter intake, stops feeding, loses colour and eventually dies of a secondary infection brought on by chronic stress. A larger tank only slows that down.

Can a common pleco live with small tetras?

As an adult, usually yes; as a juvenile, the risk is higher. An adult pleco passes 30cm and does not hunt, but it is regularly recorded rasping the slime coat off small fish resting at night, so a large size difference is a reason to say no. Once it has cleared the glass of algae it also starts on soft plant leaves, so think twice in a planted tank.

Is quarantine really necessary for new fish?

For marine fish it is close to mandatory, and for freshwater fish it is strongly advised. Ich, velvet and Brooklynella all arrive on new stock, and treating them in the display tank means treating every fish in it while copper and formalin damage corals, shrimp, snails and the nitrifying bacteria. A quarantine tank does not need to be large: a bare tank with a filter and a heater is enough.

Why is a group of six the minimum for schooling fish?

Because group size decides how safe they feel and how well aggression spreads. Keep too few and the fish switch to hiding, lose colour and refuse food, staying stressed for as long as the group stays small. Keep enough and the chasing is divided among many fish, so no single individual absorbs all of it. A minimum group size is a welfare and survival floor rather than a matter of appearance.

G-01 · Freshwater / Marine

Fish atlas

The size listed is standard length, measured without the tail fin, and the tank has to be chosen on that figure rather than on the fish in the bag. Common plecos, silver arowana and oscars are the classic examples of a cheap juvenile that outgrows the tank within a year. Water parameters are given as ranges: a wide range means an adaptable fish, and a narrow overlap with what is already in the tank means less margin when temperature or chemistry drifts. Marine entries carry two extra fields, specific gravity (SG) and reef safety, the latter deciding whether the fish can go into a coral tank at all.

Three things decide a fish purchase: adult size sets the tank, water parameters decide who it can live with, and temperament decides whether the tank ends up holding one fish.

Units: temperature in °C, hardness in German degrees (dGH / dKH), marine salinity as specific gravity at 25 °C, volume in litres. These are the values recorded for the species and do not follow the site unit switcher.

Temperament

Level

Min. tank ≤

Plant safety

43 of 43 entries

Fish atlas
Name	Adult size	Temp.	pH	Hardness	Temperament	Min. tank	Plant safe
GuppyPoecilia reticulata孔雀鱼	2.5–6 cm	22–28 °C	6.8–7.8	8–20 dGH	Peaceful	40 L	Leaves plants alone
PlatyXiphophorus maculatus月光鱼	2.5–5 cm	22–28 °C	7–8.2	10–20 dGH	Peaceful	40 L	Leaves plants alone
MollyPoecilia sphenops玛丽鱼	5–10 cm	24–28 °C	7–8.4	12–25 dGH	Peaceful	60 L	Nips new growth
SwordtailXiphophorus hellerii剑尾鱼	6–12 cm	22–28 °C	7–8.3	10–20 dGH	Peaceful	90 L	Nips new growth
BettaBetta splendens泰国斗鱼	5–6.5 cm	24–30 °C	6–7.5	2–12 dGH	Semi-aggressive	20 L	Leaves plants alone
Neon TetraParacheirodon innesi红绿灯	2.5–3.5 cm	20–26 °C	5.5–7	1–10 dGH	Peaceful	40 L	Leaves plants alone
Cardinal TetraParacheirodon axelrodi宝莲灯	2.5–3 cm	23–28 °C	5–6.8	1–6 dGH	Peaceful	40 L	Leaves plants alone
Rummy-nose TetraPetitella bleheri红鼻剪刀	4–5.5 cm	23–28 °C	5.5–7	1–8 dGH	Peaceful	60 L	Leaves plants alone
Ember TetraHyphessobrycon amandae火焰灯	1.5–2.2 cm	23–28 °C	5.5–7	1–8 dGH	Peaceful	30 L	Leaves plants alone
Black Skirt TetraGymnocorymbus ternetzi黑裙鱼	4–6 cm	20–26 °C	6–7.5	2–12 dGH	Semi-aggressive	60 L	Leaves plants alone
Serpae TetraHyphessobrycon eques红十字	3–4 cm	22–27 °C	5.5–7.5	2–12 dGH	Semi-aggressive	60 L	Leaves plants alone
Congo TetraPhenacogrammus interruptus刚果灯	6–8 cm	23–27 °C	6–7.5	2–12 dGH	Peaceful	100 L	Leaves plants alone
Harlequin RasboraTrigonostigma heteromorpha三角灯	3–4.5 cm	22–28 °C	6–7.5	2–12 dGH	Peaceful	40 L	Leaves plants alone
Chili RasboraBoraras brigittae蚂蚁灯	1.5–2 cm	23–28 °C	5–7	1–8 dGH	Peaceful	20 L	Leaves plants alone
Cherry BarbPethia titteya樱桃灯	4–5 cm	23–27 °C	6–7.5	2–12 dGH	Peaceful	60 L	Leaves plants alone
Tiger BarbPuntigrus tetrazona虎皮鱼	5–7 cm	22–28 °C	6–7.5	2–15 dGH	Semi-aggressive	80 L	Nips new growth
Denison BarbSahyadria denisonii一眉道人	10–15 cm	15–25 °C	6.5–7.8	5–15 dGH	Peaceful	200 L	Leaves plants alone
Zebra DanioDanio rerio斑马鱼	3–4.5 cm	18–26 °C	6.5–7.5	5–15 dGH	Peaceful	40 L	Leaves plants alone
White Cloud Mountain MinnowTanichthys albonubes白云金丝	2.5–3.5 cm	16–24 °C	6–7.5	2–12 dGH	Peaceful	30 L	Leaves plants alone
AngelfishPterophyllum scalare神仙鱼	10–15 cm	24–29 °C	6–7.5	2–12 dGH	Semi-aggressive	150 L	Leaves plants alone
DiscusSymphysodon aequifasciatus七彩神仙	15–20 cm	27–31 °C	5.5–7	1–8 dGH	Peaceful	200 L	Leaves plants alone
German Blue RamMikrogeophagus ramirezi荷兰凤凰	5–7 cm	26–30 °C	5.5–7	1–8 dGH	Peaceful	60 L	Leaves plants alone
Bolivian RamMikrogeophagus altispinosus玻利维亚凤凰	7–9 cm	24–28 °C	6–7.5	2–12 dGH	Peaceful	80 L	Leaves plants alone
KribensisPelvicachromis pulcher红肚凤凰	7–10 cm	24–28 °C	6–7.5	3–12 dGH	Semi-aggressive	80 L	Leaves plants alone
Convict CichlidAmatitlania nigrofasciata九间菠萝	10–15 cm	22–28 °C	6.5–8	5–20 dGH	Aggressive	100 L	Eats plants
OscarAstronotus ocellatus地图鱼	25–35 cm	23–28 °C	6–7.5	3–15 dGH	Predator	300 L	Eats plants
Jack DempseyRocio octofasciata杰克邓普西（蓝宝石）	15–20 cm	22–28 °C	6.5–8	5–20 dGH	Aggressive	200 L	Eats plants
Three-spot GouramiTrichopodus trichopterus蓝曼龙	10–15 cm	23–28 °C	6–7.8	2–15 dGH	Semi-aggressive	100 L	Leaves plants alone
Pearl GouramiTrichopodus leerii珍珠马甲	10–12 cm	24–28 °C	6–7.5	2–12 dGH	Peaceful	100 L	Leaves plants alone
Dwarf GouramiTrichogaster lalius丽丽鱼	5–7 cm	24–28 °C	6–7.5	2–12 dGH	Semi-aggressive	60 L	Leaves plants alone
GoldfishCarassius auratus金鱼	15–25 cm	10–24 °C	6.5–8	5–20 dGH	Peaceful	120 L	Eats plants
KoiCyprinus carpio锦鲤	50–90 cm	5–30 °C	7–8.5	5–20 dGH	Peaceful	3000 L	Eats plants
Peppered CoryCorydoras paleatus白鼠	5–7 cm	20–26 °C	6–7.5	2–15 dGH	Peaceful	60 L	Leaves plants alone
Sterbai CoryCorydoras sterbai花椒鼠	5.5–7 cm	24–28 °C	6–7.5	2–12 dGH	Peaceful	60 L	Leaves plants alone
OtocinclusOtocinclus vittatus小精灵	4–5 cm	21–27 °C	6–7.5	2–12 dGH	Peaceful	40 L	Leaves plants alone
Bristlenose PlecoAncistrus cirrhosus胡子异型	10–13 cm	23–28 °C	6–7.5	2–15 dGH	Peaceful	100 L	Leaves plants alone
Clown LoachChromobotia macracanthus小丑鳅	20–30 cm	24–30 °C	6–7.5	2–12 dGH	Peaceful	300 L	Leaves plants alone
Kuhli LoachPangio kuhlii苦力泥鳅	7–10 cm	24–28 °C	5.5–7	1–8 dGH	Peaceful	60 L	Leaves plants alone
Siamese Algae EaterCrossocheilus oblongus黑线飞狐	10–15 cm	24–28 °C	6.5–7.5	2–15 dGH	Peaceful	100 L	Leaves plants alone
Flying FoxEpalzeorhynchos kallopterus飞狐（泰国飞狐）	12–15 cm	23–28 °C	6–7.5	2–12 dGH	Semi-aggressive	100 L	Leaves plants alone
Red-tailed SharkEpalzeorhynchos bicolor红尾黑鲨	12–15 cm	22–28 °C	6.5–7.5	2–15 dGH	Aggressive	100 L	Leaves plants alone
Silver DollarMetynnis hypsauchen银板	12–15 cm	24–28 °C	6–7.5	2–15 dGH	Peaceful	200 L	Eats plants
Silver ArowanaOsteoglossum bicirrhosum银龙	60–90 cm	24–30 °C	6–7.5	2–12 dGH	Predator	500 L	Leaves plants alone

How to use it

Step 1Filter by water type and temperament firstRule out temperament ratings that clash with your current stock, then look at size. Pairing a peaceful species with an aggressive one is the most common way a community tank goes wrong.
Step 2Check the water parameter rangesCompare temperature, pH and hardness against every fish already in the tank. The narrower the shared window, the more the outcome depends on equipment rather than luck.
Step 3Size the tank on the adult, not the juvenileRead both the minimum tank volume and the minimum tank length. A long tank supplies swimming room and water volume supplies stability, and neither one substitutes for the other.
Step 4For marine fish, confirm reef safetyA fish marked as not reef safe will nip at corals and eat ornamental shrimp and snails, so it belongs in a fish-only tank regardless of how good the water quality is.

Frequently asked questions

How many fish can a 60cm tank hold?: There is no useful number of fish per centimetre of tank length, because the limit is set by water volume. A 60 by 40 by 40cm tank holds roughly 75 litres internally, or about 65 litres once substrate and rock are displaced: that is ample for six 4cm tetras, and already too little for one oscar that reaches 30cm. Work in that order, size the tank for the largest adult first and then count the fish that fit the remaining volume.
Why keep peaceful fish away from aggressive ones?: Because a tank is a closed space and the fish being chased has nowhere to go. An aggressive fish keeps driving its tank mate off and nipping its fins, and the peaceful fish spends its time behind the filter intake, stops feeding, loses colour and eventually dies of a secondary infection brought on by chronic stress. A larger tank only slows that down.
Can a common pleco live with small tetras?: As an adult, usually yes; as a juvenile, the risk is higher. An adult pleco passes 30cm and does not hunt, but it is regularly recorded rasping the slime coat off small fish resting at night, so a large size difference is a reason to say no. Once it has cleared the glass of algae it also starts on soft plant leaves, so think twice in a planted tank.
Is quarantine really necessary for new fish?: For marine fish it is close to mandatory, and for freshwater fish it is strongly advised. Ich, velvet and Brooklynella all arrive on new stock, and treating them in the display tank means treating every fish in it while copper and formalin damage corals, shrimp, snails and the nitrifying bacteria. A quarantine tank does not need to be large: a bare tank with a filter and a heater is enough.
Why is a group of six the minimum for schooling fish?: Because group size decides how safe they feel and how well aggression spreads. Keep too few and the fish switch to hiding, lose colour and refuse food, staying stressed for as long as the group stays small. Keep enough and the chasing is divided among many fish, so no single individual absorbs all of it. A minimum group size is a welfare and survival floor rather than a matter of appearance.