Crayfish

Molting failure (incomplete molt)

SignsStuck partway through a molt; old shell left on legs or claws; remains soft and weak after molting

PreventionKeep water quality stable and provide a calcium source. Do not touch before or after a molt and provide a hiding place. Do not house with other crayfish

Crayfish plague (water mold disease)

SignsWanders in daylight, staggers, legs turn cloudy white, dies within a short time. Non-native species carry it without symptoms

PreventionDo not bring in outdoor water or equipment used for other crayfish. Keep separate tools for each animal and dispose of tank water into the sewer

Oxygen deprivation / gill damage

SignsTilts sideways near the surface to expose gills to air; sluggish; shell darkens

PreventionKeep water shallow and provide a land area or perch. Prevent fouling with aeration and water changes at least once a week

Burn spot (shell ulcers)

SignsBlack to brown spots or holes in the shell; as it progresses, legs or claws break off

PreventionRemove leftover food and droppings from the bottom promptly. Do not let old water accumulate. It clears with molting, so support a good molting environment

Weakness at molt / stunted growth

SignsNo molt for several months; shell looks too small; reduced appetite; body color stays dull

PreventionAvoid a high-protein-only diet; offer vegetables and sinking food. Keep water temperature steady and feed lightly around molts

Heat stress

SignsStops moving in summer, refuses food, water turns cloudy and foul-smelling. Death is likely above 30°C

PreventionAvoid direct sunlight and keep water at or below 28°C. Japanese crayfish need 20°C or below. Use a fan or cooling fan

Lost claw or leg

PreventionHouse singly to prevent cannibalism. When netting, grip the body. Never touch right after a molt

First aidDo not touch the wound; rest in a hide. Cut food small and place it nearby. It regrows at the next molt, so keep the water clean

Crush injury right after molting

PreventionMove a pre-molt animal to a separate container. Keepers should not handle it either. Prevent driftwood or stones from falling

First aidWithhold food and rest in a dark place for 2–3 days until the shell hardens. If body fluid is leaking, consult an animal hospital

Wounds from cannibalism

PreventionOne animal per container as a rule. If several must be kept, use a large tank with many hides and isolate any molting animal

First aidMove to a separate container immediately and rest in clean water. If the wound turns cloudy white or smells rotten, suspect water mold infection and see a vet

Damage from falls or drying out

PreventionUse a lid with a weight to prevent escape. Handle close to the floor. Transport in a moistened container

First aidPick up with wet hands and return to tank water at once. If the shell is cracked, isolate and leave undisturbed. If it does not move, return it to water and watch for several hours

Paragonimiasis (lung fluke)

RouteEating raw or undercooked crayfish; contaminated cooking utensils

PreventionNever eat pet crayfish. Wash hands and tools with soap after contact. Watch that children do not put them in their mouths

Salmonellosis

RouteHand-to-mouth after touching tank water, shells or equipment

PreventionWash hands with running water and soap after care. Do not pour tank water into the kitchen sink

Aeromonas infection

RouteBacteria from tank water entering pinch wounds or cuts on the hands

PreventionWear gloves if you have cuts. Wash pinch wounds under running water and disinfect. See a doctor if red and swollen

Leptospirosis

RouteWater or mud contacting wounds or mucous membranes when collecting outdoors

PreventionWear gloves and boots when collecting outdoors. Wash hands afterward. Mention it to your doctor if you develop fever or muscle pain

Food

• Sinking crayfish pellets as the staple, once a day, an amount gone by the next morning
• Boiled vegetables (carrot, spinach) or fallen leaves as a supplement
• Reduce food around molts and let it eat the shed shell to recover calcium

Water

• Dechlorinated tap water. pH 6.5–8, neutral to slightly alkaline
• Change one-third to half the water weekly; twice weekly in summer. Keep temperature difference within 2°C

Toys & play

• PVC pipe or broken flowerpot pieces for burrowing play
• Driftwood and stones to create climbing spots and a land area
• Sinking fallen leaves (zelkova, oak) serve as both food and cover

Nest, bed & hideout

• At least one PVC pipe or clay pipe the whole body fits into
• A separate dark, quiet hide for molting

Bedding & litter

• 2–3 cm of coarse sand or fine gravel; a depth that is easy to clean
• A bare tank (no substrate) is also fine; dirt is visible and easy to manage
• Avoid fine soil, which clouds the water

Cage / housing material

Glass or plastic aquarium. A lid with a weight is essential

Size & space

At least a 30 cm tank per animal. Japanese crayfish need 45 cm or more plus cooling

Layout

• Keep water shallow, 2–3 times body height, with a land area it can climb onto
• Two or more hides. Aeration is essential
• Arrange so it cannot escape by climbing the filter intake or cords

Placement notes

• Out of direct sunlight and heater drafts
• A quiet spot with little vibration or noise, out of reach of other pets

Exercise, free-roam & walks

• No walks needed. Do not take it out of the tank
• Let it exercise on climbing spots and hides in the tank
• To lift it, pinch the top of the body between thumb and forefinger

Temperature & humidity

TemperatureRed swamp crayfish 15–25°C (max 28°C). Japanese crayfish 10–18°C

HumidityNot applicable; kept in water. Keep the land area always moist

Summer & winter

• In summer keep at or below 28°C with a cooling fan, room air conditioning or shade
• In winter no heating is needed, but do not let it freeze. Reduce food

Nail trimming

No nail trimming. Chipped claws and legs regrow at molt, so do not cut or touch them

Brushing, skin & coat care

Do not scrub the shell; keep it clean with water changes. Leave the shed shell a few days to be eaten, then discard

Other care

Withhold food and avoid disturbance before a molt. If old shell remains, gently remove it with a moistened cotton swab the next day or later

Protection from predators

• Cats, dogs and birds target it; mind the lid and placement
• Outdoor housing risks predation by raccoons and herons, and escape
• A tankmate crayfish is the biggest enemy. Keep one per tank as a rule

Foreign-body ingestion

Watch that children do not put small crayfish or shed shells in their mouths. Parasites are a risk; if swallowed, consult a pediatrician

Being stepped on

Stepping on an escaped crayfish cracks the shell and is fatal. If lost, dim the lights and search the floor and under furniture with wet hands

Getting pinched

Legs can be lost when caught in gaps in filters or stones. Make gaps much wider than the body. If trapped, do not pull; remove the stone

Falls

A fall from the tank cracks the shell. Lift only just above the water; if it falls, pick it up with wet hands and return it to water at once

Escape

A weighted lid and sealed cord gaps are essential. If it escapes, search indoors; even if found, never release it outdoors (illegal)

Safe release procedure

1. Stay calm, stop moving, and lower your hand with the crayfish to the water surface
2. Submerged in water, it usually lets go on its own
3. If not, gently press the base of the claw up and down to open it
4. If it still holds on, wait a little. Do not pull by force

After the release

Wash the wound under running water and disinfect. See a doctor if bleeding does not stop, or it becomes red, swollen or hot. Wear gloves if you have cuts on your hands

What to tell the vet & what to bring

Species, years kept, water temperature, water-change frequency, date of last molt, any tankmates. Bring photos and a small sample of tank water

Checking consciousness, breathing & heartbeat

• Gently touch the antennae or legs and check for a reflex
• Confirm breathing by gill movement and water flow at the mouth
• Lift it and check whether it curls its tail in resistance

Stopping bleeding

• Crayfish blood is blue and clots readily. Leave it undisturbed
• Lost parts seal naturally. Prevent infection with clean water
• If fluid loss does not stop, consult an animal hospital at once

Transport

• Carry in a lidded container lined with moistened paper towels
• In summer add an ice pack on the outside; avoid vibration and direct sunlight