Schooling freshwater fish

A schooling fish swims in formation with its own kind: rummy-nose and cardinal tetras turn together. A shoaling fish holds a loose group instead: corys, kuhli loaches and hatchetfish stay near each other without formation. Both are on this list, and both need numbers. Six is the floor for most species and each profile lists the group it needs. Kept in twos and threes, a schooling fish hides, loses color, or takes it out on tank mates, which is where most fin nipping by tetras and barbs comes from. Six different tetras are six lonely fish; the school is one species.

1. 01

   Six is the floor

   Each profile lists the group its species needs

2. 02

   One species

   Six different tetras do not make a school

3. 03

   More is calmer

   A dozen hides less and nips less than six

4. 04

   Length over height

   A school runs, so a long tank beats a tall one

The ember tetra is 0.8 inches (2 cm) for 9 gallons (35 liters), marked easy, and the smallest school here. The black neon tetra is marked beginner at 1.4 inches (3.5 cm) for 16 gallons (60 liters). The glowlight tetra is 1.6 inches (4 cm) for 18 gallons (70 liters), and the lemon tetra 2 inches (5 cm) for 17 gallons (65 liters); both take a pH up to 7.5 or 8. The x-ray tetra takes the same and lists 18 gallons (70 liters). The Congo tetra is the big one, 3.1 inches (8 cm) for 24 gallons (90 liters), marked easy, with fins that only show in a group with room. The serpae tetra is the one that nips when kept short-handed.

The cherry barb is marked beginner and peaceful at 2 inches (5 cm) for 20 gallons (75 liters), the barb for a community tank. The tiger barb is the same size and rating and marked aggressive, because a small group nips everything; a group of eight or more mostly nips each other. The Odessa barb is 1.8 inches (4.5 cm) for 61–77°F (16–25°C). The pearl danio takes the same cool range at 2.4 inches (6 cm) for 18 gallons (70 liters). The white cloud mountain minnow is marked beginner at 1.6 inches (4 cm) and lists 57–72°F (14–22°C), a school for an unheated tank. The celestial pearl danio is 0.8 inches (2 cm) for 9 gallons (35 liters), marked easy.

The panda cory shoals on the sand at 2 inches (5 cm) for 15 gallons (55 liters), marked easy. The pygmy cory is the one cory that schools in mid-water, 1.3 inches (3.3 cm) for 13 gallons (50 liters). The kuhli loach is a 3.9 inch (10 cm) eel-shaped fish for 20 gallons (75 liters), marked easy, that only comes out in a group. The otocinclus grazes algae in a shoal at 2 inches (5 cm) for 20 gallons (75 liters), marked medium because it starves in a new tank. The marbled hatchetfish holds the surface at 1.6 inches (4 cm) for 32 gallons (120 liters) and jumps at any gap in the lid. The golden pencilfish hangs just under the surface at 2.4 inches (6 cm).

The dwarf rainbowfish is the rainbowfish for a smaller tank at 2.8 inches (7 cm) for 20 gallons (75 liters), marked easy. The red rainbowfish reaches 5.5 inches (14 cm) and lists 34 gallons (130 liters). The silver dollar is 5.9 inches (15 cm) and lists 70 gallons (265 liters), a plant eater that wants a group and a long tank. The scissortail rasbora is 5.5 inches (14 cm) for 45 gallons (170 liters), marked easy. The glass catfish schools in mid-water at 2.8 inches (7 cm) for 30 gallons (115 liters), marked easy and peaceful. The clown loach is the biggest shoaling fish on this page, 11.8 inches (30 cm) for 75 gallons (285 liters), sold small and kept for decades.