Dwarf Crayfish (CPO) Care: The Small Crayfish That Leaves Fish Alone

The CPO (Cambarellus patzcuarensis 'Orange'), also sold as the orange dwarf Mexican crayfish, tops out around 1.5 to 2 inches with its claws. That's too small to catch healthy fish, so it fits in a community tank where a regular crayfish would be a problem. Give it a 10-gallon or bigger tank kept at 60 to 75°F, hard water, plenty of caves, and a calm spot away from strong current. It will live about 2 to 3 years.

There are two exceptions. A CPO will still eat dwarf shrimp, small snails and very small or sick fish if it can catch them. And it's illegal to own in some states, so check yours before you order.

Why the CPO is different from a "real" crayfish

In our post on whether crayfish can live with fish, the general answer was "usually not." Most aquarium crayfish, like the electric blue (Procambarus alleni), grow to 4 to 6 inches. They have claws big enough to grab a sleeping fish off the bottom and strong enough to shred plants.

A CPO is a different animal. Adults measure 4 to 5 cm (1.6 to 2.0 inches) including the claws, and plenty stay closer to 1.2 to 1.6 inches. Their claws are about the size of a grain of rice. A healthy danio or White Cloud can easily get out of reach.

The orange color comes from an aquarium mutation. Wild C. patzcuarensis are brown with gray or blue tints, and the orange form is rarely found in the wild. The species is native to one small area in Michoacán, Mexico: Lake Pátzcuaro, sitting at about 6,700 feet (2,035 m), plus a few nearby springs. The IUCN lists it as Endangered. Every CPO you see in a store comes from tank-bred stock.

Tank setup

• Tank size: 10 gallons is a comfortable minimum for a few. Some sellers say 5 gallons is fine for one, but a bigger floor gives more room for territories.
• Temperature: 60 to 75°F. Some care sheets stretch it to 80°F, but you're better off staying cool. In many homes they don't need a heater at all. Our cold-water heater guide explains how to decide.
• Water: pH 6.5 to 8.0, with moderate to hard water (GH 3 to 25, KH 1 to 15). Hard water gives them the minerals they need to build a new shell.
• Cover: Use a tight lid and plug any gaps around tubing. Crayfish of any size will climb filter intakes and cords and get out.
• Substrate: Sand or small, smooth pebbles. They spend their day picking through the bottom, and our substrate guide covers what holds up in a river tank.

Caves matter more than anything else here. Give each crayfish at least one hiding spot, and add a few extra. Short lengths of 3/4-inch PVC, small clay pots on their side, stacked flat stones and the gaps under driftwood all work. If there are fewer caves than crayfish, they spend the day fighting over them.

How much flow

This crayfish comes from a lake, not a river. It does fine with a gentle current, but it doesn't want to stand in a torrent all day.

In a one-way manifold river tank, keep CPOs at the outflow end where the water slows down. You can also stack rocks to make a still pocket behind them. If a crayfish keeps getting pushed across the sand or wedges itself in a corner, the flow is too strong where it lives. Plants that grip rock, like java fern and anubias, break up the current and give it cover.

Always put a sponge pre-filter on the intake. Juvenile CPOs are the size of a grain of rice and will get pulled straight into a powerhead or filter.

Tank mates

Good matches:

• Fast, mid-water and top-water fish: zebra danios, White Cloud minnows, rosy barbs
• Sturdy bottom fish that hold their ground: bristlenose plecos, hillstream loaches
• Larger snails: mystery snails and adult nerites, which have shells too big and hard for a CPO
• Adult Amano shrimp, which are big and quick enough to get away

Risky:

• Cherry shrimp and other dwarf shrimp. Adults usually escape, but shrimplets and freshly molted shrimp get eaten. If you want a big shrimp colony, keep them in a different tank.
• Small snails like ramshorns and bladder snails will get picked off. That may be what you want, but it's worth knowing.
• Fish that sleep on the bottom, plus very small fry.

Bad matches:

• Anything big enough to eat a 1.5-inch crayfish: most cichlids, adult goldfish, large loaches, puffers, and musk turtles.
• Other crayfish species, which will fight with or kill CPOs.
• Fish that pick at the bottom will hunt freshly molted CPOs.

In a fish tank, plan on 1 male and 2 to 3 females per 10 gallons, and add rock work and caves for every animal. Males are more likely to spar over territory.

Molting: the dangerous few days

Crayfish grow by shedding their whole shell. Juveniles molt often and adults less. For a day or two afterward the new shell is soft, the crayfish can barely defend itself, and it hides.

What that looks like and what to do:

• A "dead crayfish" in the tank is usually an empty shell. Look for a clean, see-through split between the body and tail. Leave it in place. The crayfish will eat it to get the calcium back.
• A crayfish hiding for days and not eating is often about to molt or has just molted. Leave it alone.
• Failed molts, where the crayfish gets stuck partway out or dies just after molting, usually point to low minerals or poor water. Test GH and keep it in range. A piece of cuttlebone in the tank adds calcium as it slowly dissolves.
• Copper is toxic to all invertebrates. Read the label on any medicine or plant fertilizer before adding it, and don't put new fish in until they've been quarantined somewhere else.

The same rule from crayfish keepers covers ammonia and nitrite: they hit inverts harder than fish. Only add CPOs to a fully cycled tank, and check it with a test kit for the first few weeks.

Feeding

CPOs are scavengers and eat almost anything that reaches the bottom. A simple routine:

• A sinking invertebrate pellet or crumbled algae wafer every day or two.
• Frozen bloodworms, brine shrimp or mosquito larvae once or twice a week.
• Blanched zucchini or spinach now and then.
• Dried leaves. Fall is a good time to stock up, and our post on aquarium-safe leaves explains which ones to collect. The crayfish graze on the leaves and the film that grows on them.

In a tank with fish, make sure some food actually reaches the bottom. If the fish get all of it, the crayfish start hunting for something else. For the bigger picture, see what crayfish eat.

Breeding happens on its own

Keep a male and a female together in a cool, settled tank and you'll probably get babies. The female carries up to about 60 eggs under her tail. When the eggs turn dark they're fertilized, and they hatch in roughly 3 to 4 weeks.

There's no larval stage. The young come out as tiny, complete crayfish and feed themselves from day one. Crayfish are cannibals, though. In a tank full of fish and adults, few young survive unless there's thick moss or a pile of leaf litter for them to hide in. If you want more, move the female with eggs to her own 5- or 10-gallon tank with a sponge filter.

What they cost and where you can't have them

As of October 2026, US online sellers list single CPOs for about $11 to $21. Trios and breeding groups run about $35 to $50, and a female carrying eggs costs around $30.

Check the law before you buy. Several states restrict non-native crayfish, and one major US breeder won't ship CPOs to Arizona, California, Maine, Pennsylvania, Virginia, Washington, or Wisconsin. Pennsylvania restricts nearly all live crayfish. Other states ban only certain species, like marbled or red swamp crayfish, and the lists change. Check your state's fish and wildlife rules first. Never let a crayfish loose outdoors, in any state.

Before you bring one home

1. Confirm CPOs are legal where you live.
2. Have a cycled tank of 10 gallons or more, holding steady at 60 to 75°F with GH of at least 3.
3. Add at least one cave per crayfish, plus spares.
4. Fit a tight lid and put sponges on every intake.
5. Pick a calm area of the tank, away from the main current.
6. Leave molted shells in the tank, and keep copper out.

Related: Are Clams Alive?

Sources (5)

• Cambarellus patzcuarensis (Wikipedia)
• Orange dwarf Mexican crayfish care guide, Aquatic Arts
• Mexican dwarf crayfish care, Fishkeeping World
• Dwarf orange crayfish care sheet, The Shrimp Farm
• Preventing crayfish invasions, InvasiveCrayfish.org

Photo: CPO male by HellSpawn754, CC0.