Meet Your New Best Friend: The Mosquito Fish (Gambusia affinis)

Looking for a natural way to cut down on mosquitoes around your property? Meet the Gambusia affinis. These tiny, hardworking fish are a "secret weapon" in our integrated mosquito control program.

Small Fish, Big Appetite

Don't let their size fool you. These live-bearing fish have a ferocious appetite specifically for mosquito larvae. By eating the mosquitoes before they ever have a chance to fly, these fish provide a 24/7 biological defense system for your troughs and ponds.

How many do I need?

You don’t need a whole school to make a difference! As a general rule:

• 6 mosquito fish are enough to patrol an area of roughly 48 square feet (for example, a 6’x8’ surface area).

Where can they live? (The Golden Rule)

To protect our local ecosystem, we follow Oregon Department of Fish and Wildlife (ODFW) guidelines (ORS 498.222).

Mosquito fish can ONLY be stocked in "Aquaria": These are self-contained systems that do not drain into or get fed by natural waterways (like creeks, streams, sloughs, or ditches).

• ✅ YES: Stock troughs, isolated ornamental ponds, and self-contained water features.
• ❌ NO: Ponds in floodplains, or any water source connected to natural lakes or streams. 

Care & Maintenance: Keeping Your "Finny Friends" Happy

While mosquito fish are low-maintenance, a little knowledge goes a long way in ensuring they survive and thrive year-round.

Winter Hibernation

Don't panic if you don’t see your fish when the temperature drops! During the winter months, mosquito fish move to the bottom of their habitat and enter a period of inactivity. They stop feeding and "sleep" through the cold. In most cases, they will survive the winter and become active again in the spring as soon as the water warms up.

When to Feed (and When Not To)

In an established pond or a trough that’s been sitting for a while, nature provides an all-you-can-eat buffet of larvae and microorganisms. In these cases, no supplemental feeding is required.

However, if you are placing fish into:

• A newly constructed pond
• A freshly scrubbed stock trough
• A recently cleaned water feature

...they may need a little help until natural food sources move in! You can give them a boost with a small amount of fish flakes, or even pantry staples like crackers, stale bread, or finely crumbled dog food.

Ready to recruit your tiny task force?

North Morrow Vector Control provides these fish to residents free of charge for approved locations.

Requesting fish is easy:

1. Call us: Dial (541) 481-6082. Just let us know your name, address, phone number, and the size/number of troughs or ponds you have.
2. Online: Simply fill out the Fish Request Form below!

Delivery Details: Our Field Technicians will deliver your fish as soon as possible. Once they arrive, we will let you know verbally or leave a bright orange door hanger to confirm your new "patrol" is on duty!

Fish Request Form