5 Best Aquarium Fish That Don’t Need a Heater

Celestial Pearl Danio (Galaxy Rasbora)

Celestial Pearl Danios are often mistaken for delicate tropical fish, but they naturally come from cooler highland ponds and do very well in unheated aquariums kept between 68–74°F (20–23°C).

They are small, peaceful schooling fish that feel safest in groups of at least 6–10. A heavily planted tank with gentle flow brings out their best coloration and reduces stress.

While they can adapt easily, they are sensitive to poor water quality, so stable parameters and regular maintenance are essential.

White Cloud Mountain Minnow

White Cloud Mountain Minnows are one of the most reliable true coldwater aquarium fish available. They thrive in temperatures ranging from 60–72°F (15–22°C) and can even handle brief temperature drops better than most species.

These active swimmers prefer being kept in groups and do best in longer tanks with open swimming space. Their hardiness makes them ideal for beginners, classrooms, or aquariums in cooler rooms where heaters aren’t practical.

Neocaridina Shrimp

Neocaridina shrimp, including popular varieties like Cherry Shrimp, are excellent coldwater-tolerant invertebrates that thrive in unheated tanks between 65–75°F (18–24°C).

They are low-bioload, easy to care for, and constantly graze on biofilm and algae. Stability is more important than temperature for shrimp, so avoid sudden water changes and maintain consistent parameters.

Live plants, mosses, and hiding spaces help shrimp feel secure and encourage breeding.

Clown Killifish

Clown Killifish can live comfortably in unheated aquariums kept around 68–74°F (20–23°C) as long as the temperature remains stable.

They are surface-dwelling fish that prefer calm water, floating plants, and subdued lighting. Because they spend most of their time near the surface, a secure lid is important to prevent jumping.

Though small and peaceful, they display bold patterns and unique behavior that make them stand out in nano or planted tanks.

Platy

Platies are hardy livebearers known for their adaptability and resilience, making them a solid choice for unheated aquariums at room temperature, typically 68–74°F (20–23°C).

While warmer water increases their breeding rate, they remain healthy and active in cooler setups. Platies are social fish that do best in small groups and appreciate open swimming areas along with some plant cover.

Their ease of care makes them popular for both beginner and community tanks.

A Cooler Tank Can Still Be Full of Life

Skipping a heater doesn’t mean sacrificing color, movement, or personality in your aquarium. By choosing species that naturally tolerate cooler temperatures and focusing on stable conditions, you can build a thriving tank that’s simple, affordable, and rewarding.

Whether you prefer schooling fish, shrimp, or peaceful community setups, coldwater-friendly species offer plenty of options for a healthy and active aquarium year-round.