Brook stickleback

Culaea inconstans

FreshwaterFish

Care at a glance

Temperature: 50–68°F (10–20°C)
pH: 6.5–8.0
Adult size: 1.8 in (4.5 cm)
Minimum tank: 20 gal (75 L)
Temperament: Aggressive
Social behavior: Solitary
Swim level: Middle
Difficulty: Difficult
Breeding: No record
Rarity: Very rare
Origin: United States, Canada
Family: Gasterosteidae

Overview

This is a territorial, scrappy fish, especially the males at breeding time, so it's best kept on its own or with careful coldwater tankmates in a 75 liter or larger tank. It tends to hang in the middle of the water and defend a patch. It's a poor match for the usual community fish and won't take dried food well, so plan on live or frozen bloodworms, brine shrimp, and daphnia. It's a difficult fish overall because of the cool water and feeding demands.

In the wild

The brook stickleback lives in cool, slow streams, small rivers, and ponds across the northern United States and Canada, in clear water with plants for cover. This is a coldwater fish, not a tropical one, so it needs a cool tank, roughly 10 to 20 C, and usually a chiller in a warm room. Give it dense planting and quiet water rather than strong flow.

Good to know

Culaea inconstans is the only species in its genus, in the family Gasterosteidae. It's a small fish, around 4 to 5 cm, and instead of scales it has bony plates and small spines along the back. It's a nest builder: the male weaves a nest from plant material held together with a glue-like secretion, then guards the eggs until they hatch. The IUCN lists it as Least Concern.

Did you know

The male builds a barrel-shaped nest off plant stems, gluing it together with a sticky protein his kidneys produce, then fans water through it to keep the eggs oxygenated. He'll even patch and rebuild the nest if it gets damaged while he's guarding it.