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. Most corys, the kuhli loaches and the marbled hatchetfish stay near each other without formation. The pygmy and dwarf corys and the silver and Scherer's hatchetfish are marked schooling. Both kinds are on this list, and both need numbers. Six is the floor for most species, and most profiles give the group size. 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

   Most profiles list the group their 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 one of the smallest schools here. The Tambopata glass tetra is the smallest tetra on this page at 0.7 inches (1.9 cm). The black neon tetra is marked beginner at 1.4 inches (3.5 cm) for 10 gallons (38 liters). The glowlight tetra is 1.6 inches (4 cm) for 10 gallons (38 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 biggest of these at 3.1 inches (8 cm) for 24 gallons (90 liters), marked easy. Its fins only show in a group with room. The serpae tetra and the black widow tetra both nip when kept short-handed.

The cherry barb is marked beginner and peaceful at 2 inches (5 cm) for 14 gallons (54 liters), the barb for a community tank. The tiger barb has the same rating at 2.8 inches (7 cm) and is 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 11 gallons (41 liters), marked easy. The pygmy cory schools in mid-water at 1.3 inches (3.3 cm) for 10 gallons (38 liters). The dwarf cory is the only other cory that does. The kuhli loach is a 3.9 inch (10 cm) eel-shaped fish for 17 gallons (65 liters), marked easy, that only comes out in a group. The otocinclus grazes algae in a shoal at 2 inches (5 cm) for 12 gallons (46 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 a 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 one of the biggest shoaling fish on this page, 11.8 inches (30 cm) for 75 gallons (285 liters). It is sold small and kept for decades.