Ancient fish

Macrogyrodactylus

SignsA parasite specific to Polypterus. White thread-like worms on the body and fins, rubbing against objects, fins becoming ragged

PreventionAlways treat new arrivals in a separate tank for 2–4 weeks. Inspect the body surface at purchase

Aeromonas infection

SignsHemorrhagic spots on the body, raised scales, swollen abdomen, bulging eyes. Prone to break out when water quality deteriorates

PreventionChange 1/3 of the water weekly to keep nitrate from building up. Do not use old food; remove leftovers the same day

Columnaris

SignsThe mouth or tips of the tail fin turn white and crumble as if dissolving. Progresses fast and can kill within days

PreventionAvoid sudden temperature changes and abrasions. Quarantine new fish; isolate and see a vet immediately if found

Ich (white spot disease)

SignsMany white dots on the body and fins. Rubbing against the substrate, clamped fins. Common after a temperature drop

PreventionKeep water temperature constant with a heater. Match new water temperature during changes. Quarantine new arrivals

Failed estivation (lungfish)

SignsThe mucus cocoon dries out completely during estivation, the fish is thin and motionless, or stays sunk and refuses food after waking

PreventionDeliberately avoid estivation in captivity. Keep water level and temperature stable; use an auto-feeder and maintain water level during long absences

Obesity / fatty liver

SignsAbdomen always swollen, labored swimming, sluggish movement. Common in datnoids and lungfish and a cause of sudden death

PreventionFeed adults 2–3 times a week and avoid fatty foods. Give only what is eaten with no leftovers

Drying out after jumping

PreventionHeavy lid and sealed cable gaps. Keep the water level at least 5 cm below the lid. Watch out at night and after water changes

First aidDo not grab with dry hands; return it to the tank with wet hands. Even with dry skin, it may recover if still breathing. See a vet the same day

Lungfish bites (tankmates)

PreventionLungfish should be kept alone as a rule. If you must mix, use a divider and take care when putting your hands in

First aidIsolate the bitten fish and photograph the wound. If the wound is deep or scales are torn off, see a vet the same day. Keep the water clean

Abrasions to the snout or jaw

PreventionCaused by ramming into glass or rocks. Use decor without sharp edges and avoid startling the fish. Dim lighting

First aidPhotograph the wound and keep the water clean with water changes. See a vet the same day if white fungus or dissolving appears

Heater burns

PreventionBottom-resting fish easily touch the heater. Always fit a heater guard and mount it away from the bottom

First aidPhotograph the reddened area. Keep the water clean to prevent secondary infection. See a vet the same day if the area is extensive

Atypical mycobacteriosis (fish tank granuloma)

RouteInfection through cuts exposed to tank water or fish

PreventionDo not put your hands in the tank if you have cuts. Wash hands after work. See a dermatologist if a lump develops

Salmonellosis

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

PreventionWash hands with soap after tank work. Do not wash equipment in the kitchen. Do not pour tank water down the kitchen sink

Aeromonas infection (humans)

RouteTank water contacting a wound, or fish bites

PreventionIf bitten by a lungfish, rinse under running water and disinfect. See a doctor if swelling or fever develops

Leptospirosis

RouteDirty tank water contacting wounds or mucous membranes

PreventionWear gloves during water changes. Never get tank water in your mouth. See a doctor if fever or muscle pain develops

Food

• Polypterus: mainly sinking pellets for carnivorous fish, supplemented with frozen bloodworms or small fish
• Lungfish and datnoids: train onto pellets, with frozen shrimp or fish fillet a few times a week
• Juveniles daily, adults 2–3 times a week. Give what is eaten within 5 minutes

Water

• Use dechlorinated water. Change 1/3–1/2 weekly and match the new water temperature
• Water temperature 24–28°C, slightly acidic to neutral. Keep ammonia and nitrite at zero at all times

Toys & play

• Provide hides the fish can fit into, such as driftwood or PVC pipe, for security
• Make use of nighttime foraging by scattering sinking food
• Add a pump for current to encourage swimming (keep it gentle for lungfish)

Nest, bed & hideout

• A PVC pipe or driftwood tunnel longer than the fish's body
• For datnoids, create a calm spot with dim lighting and a dark background

Bedding & litter

• A bare-bottom tank (no substrate) is easiest to clean and manage
• If using substrate, a thin layer of fine, smooth sand (note that lungfish swallow sand)
• Avoid large gravel, which can lodge in the mouth

Cage / housing material

Glass or acrylic tank. Heavy lid (glass or acrylic) and sponge to seal gaps

Size & space

90 cm for small Polypterus species; 120–180 cm or more for large species, lungfish, and datnoids

Layout

• Strong filtration with a hang-on or canister filter
• Heater with a guard, mounted away from the bottom
• Seal gaps around cables and hoses to prevent jumping

Placement notes

• A full tank can weigh several hundred kg; check the floor strength
• Avoid direct sunlight and vibration; prepare for power outages

Exercise, free-roam & walks

• No walks. Allow time for nighttime bottom-crawling and turn lights off at night
• Clean the tank weekly, quietly, so as not to startle the fish
• Always check where a lungfish's mouth is when putting your hands in

Temperature & humidity

TemperatureWater temperature 24–28°C. Below 22°C or above 30°C causes ill health

HumidityDo not seal the space between the water surface and lid too tightly. Air-breathing fish need air at the surface

Summer & winter

• Summer: use a cooling fan or chiller to keep it from exceeding 30°C
• Winter: split heating across two heaters in case one fails

Nail trimming

No nail trimming. Instead, do a weekly 1/3 water change and filter cleaning. Manage nitrate with water tests

Brushing, skin & coat care

No brushing. Check both flanks at feeding time for white worms or white spots

Other care

Lungfish have well-developed tooth plates and a strong bite. Feed with tongs or chopsticks and keep fingers away

Protection from predators

• Use a heavy lid so cats cannot climb onto it
• Bites from tankmates. Lungfish alone; datnoids only with same-sized fish
• Keep children from putting their hands in. Lungfish bites are deep

Foreign-body ingestion

Swallow substrate, heater suction cups, and small tankmates whole. Keep anything that fits in the mouth out. If it cannot spit it out and the belly swells, see a vet the same day

Being stepped on

Fish that have jumped can be stepped on in a dark room. If you hear something hit the floor, turn on the lights and look. If stepped on, check for bleeding or fractures

Getting pinched

Getting caught between lid and glass, or fins sucked into the filter intake. Fit a sponge over the intake

Falls

Jumping onto the floor causes dried skin and bruising. Lower the water level and weight the lid. Return a fallen fish gently with wet hands

Escape

The only escape is jumping. If missing, check behind the tank and under furniture. Even if dry, return it and see a vet if still breathing

Safe release procedure

1. Stay still and relax; wait for the fish to let go on its own
2. Keep the fish's head underwater and support its body with a wet cloth
3. If it does not release, run water against the side of its mouth to stimulate it
4. Once released, return the fish to the tank and wash your hand under running water

After the release

Rinse the wound under running water and disinfect. See a doctor for deep wounds, swelling, or fever and tell them you were bitten by a fish

What to tell the vet & what to bring

Bring water temperature, pH, and ammonia readings, water-change frequency, date of acquisition, tankmates, and photos of the symptoms

Checking consciousness, breathing & heartbeat

• Gill cover movement (normal is roughly 60–100 per minute, varies by species)
• Interval between air breaths (normal is once every few minutes to 10-plus minutes)
• Response to touch and body posture (lying on its side or upside down is critical)

Stopping bleeding

• Pressure cannot be applied to stop bleeding in fish. Move to clean water and keep quiet
• Photograph the bleeding site and keep the water clean
• See a vet the same day if bleeding continues or scales are coming off

Transport

• Put tank water and air in a plastic bag, keep warm in a styrofoam box for transport
• For lungfish, use less water and double-bag to guard against bite-throughs