Three-spined stickleback

Gasterosteus aculeatus

FreshwaterFish

Care at a glance

Temperature: 50–64°F (10–18°C)
pH: 6.5–8.0
Adult size: 3.1 in (8 cm)
Minimum tank: 20 gal (75 L)
Temperament: Mostly peaceful
Social behavior: Schooling
Swim level: Middle
Difficulty: Medium
Breeding: Medium
Rarity: Common
Origin: Circumarctic and temperate Northern Hemisphere: coastal Europe, northern Asia (incl. Japan), and North America; freshwater, brackish, and marine
Family: Gasterosteidae

Overview

Keep a group of at least six in a tank of 75 liters or more, kept cool between 10 and 18 C with a pH around 6.5 to 8. Outside breeding they shoal peacefully in the middle of the water column, but during the season males turn territorial and will bite and chase other fish away from their nests, so use a roomy, heavily planted layout or a single male to cut down on fighting. They are carnivores that often refuse dry flake, so feed live or frozen daphnia, bloodworm, gammarus, and brine shrimp. Do not house them with warm water tropical fish, since temperatures above about 20 C stress them. If you collect wild native stock, check your local rules first and never release tank fish back into the wild.

In the wild

Three-spined sticklebacks live across the cool temperate Northern Hemisphere, in coastal streams, ditches, and ponds throughout Europe, northern Asia, and North America. They move between freshwater, brackish, and full saltwater, but most aquarists keep them in hard, slightly alkaline freshwater at a pH of about 6.5 to 8. This is a coolwater fish, not a tropical one, so leave the tank unheated and hold it between 10 and 18 C. Give them a heavily planted 75 liter tank or larger, with strong filtration or an airstone, since they need cool, well oxygenated water.

Good to know

This is Gasterosteus aculeatus, a small fish in the family Gasterosteidae, reaching around 8 cm. It is anadromous and euryhaline, meaning some populations migrate between salt and fresh water and the fish can handle a wide range of salinity. Instead of scales it has bony plates along the flanks, and the males build a glued nest from plant fibers to raise the eggs.

Did you know

Sticklebacks are one of the most studied fish in biology, largely because of their courtship. In spring the male's throat and belly flush bright red, he builds a tunnel shaped nest, and he performs a zigzag dance to lead a female inside. Once she lays, he guards the eggs alone and fans fresh water over them with his fins until they hatch.