Signal crayfish

Water parameters

Minimum tank: 200 L per individual at harvest size.

Feed and growth

Feed protein

30% target

Daily feed (warm)

1.50% of body weight

Daily feed (cool)

0.50% of body weight

Max density

10 g per litre

A 200 g adult eats about 3.0 g of feed per day at optimum. 10 fish at adult size: ~30 g daily.

Legality

Rules vary by jurisdiction and change over time. Verify with your local fisheries or wildlife authority before stocking.

Unlisted jurisdictions default to "check local regulations".

Origin and habitat

Native to the Columbia River basin of western North America, across British Columbia, Washington, Oregon and Idaho, and introduced widely beyond it. Deliberately brought to Sweden and Finland in the late 1950s and 1960s to rebuild crayfish fisheries that plague had wrecked, it carried the very pathogen it was meant to work around. Signal crayfish shrug off crayfish plague, the water mould Aphanomyces astaci, while every European species is lethally vulnerable, so the introductions spread the disease and pushed native noble crayfish and others toward collapse. The species is now the most widespread non-native crayfish in Europe, established in dozens of countries from Scandinavia and Britain through France, Germany and Central Europe, and also in Japan. Adults usually run 6–9 cm but can reach 16–18 cm and around 80–200 g, marked by the pale blue-green patch at the claw hinge that gives the common name. The flesh is firm and sweet.

Climate and outdoor ponds

Climate

temperate (handles seasonal swings)

USDA zones

4–8 (winter low around -34°C or warmer)

Heating needed

no

Cooling needed

no

Care notes

A cool-water crayfish, best around 14–22°C, though its culture is dominated by biosecurity rather than husbandry. Growth is moderate, roughly 80–200 g in 12 to 18 months on crayfish pellet of 28 to 35 percent protein, with feed conversion near 2 to 3. Stock by bottom area, about 8 to 15 per square metre, and give shelter. Signal crayfish are tougher and more aggressive than noble crayfish, which makes them easy to rear but hard on everything around them: they burrow forcefully enough to undercut pond banks and levees, and they prey on small fish, invertebrates and plant roots, so solid-bottomed tanks are safer than earthen ponds. The decisive issue is disease. Because they carry crayfish plague, they must never be held anywhere they could reach native European crayfish. Across the European Union the species is on the list of invasive alien species of Union concern, which bars keeping, breeding, transport, sale and release, and Britain regulates it under the Wildlife and Countryside Act; Finland has pressed for an outright ban on stocking and culture. In their native Pacific Northwest they are harvested and farmed without those concerns. For European systems, slower-growing native options such as noble crayfish or the narrow-clawed Astacus leptodactylus are the responsible choice.

Further reading

• Aquaponics water chemistry: balancing pH for fish and plants
• Fish for aquaponics: tilapia vs everything else