Ornamental fish (freshwater)

Ich (white spot disease)

SignsWhite dots scattered over body and fins, rubbing against objects, clamped fins

PreventionAvoid sudden temperature swings. Quarantine newcomers in a separate tank for 1–2 weeks

Fin rot

SignsFin edges turn cloudy white and shorten as if dissolving, redness, lethargy

PreventionNever skip water changes. Avoid overcrowding; keep out driftwood or fish that damage fins

Swim bladder disorder (flipping)

SignsFloats belly-up, sinks and cannot right itself, tends to float after eating

PreventionCommon in round goldfish such as ryukin. Keep water temperature stable in winter; soak food and feed small amounts

Fungal infection (cotton wool disease)

SignsCotton-like white fluff on the body surface, spreading from wounds

PreventionPrevent injuries. Avoid low temperatures and dirty water; remove dead fish immediately

Aeromonas infection

SignsSwollen belly with scales sticking out like a pine cone, red hemorrhagic spots on body, bulging eyes

PreventionCaused by poor water quality and overcrowding. Do not overfeed; siphon debris from the bottom

Nitrite / ammonia poisoning

SignsGasping at the surface, staying motionless, dark red gills, sudden successive deaths

PreventionKeep few fish right after setting up a tank. Test weekly with test strips and lower levels with water changes

Jumping out of the tank

PreventionAlways use a lid. Block gaps with plastic sheet. Do not startle the fish; do not fill the water too high

First aidReturn it gently with wet hands. Even if motionless, wait several hours in a spot with weak current. Add slime-coat protectant at the labeled dose

Torn fins or body lacerations

PreventionAvoid sharp driftwood and rocks. Do not house incompatible fish together (two bettas, aggressive species)

First aidRemove the attacker or cause and isolate. Give a 0.5% salt bath in clean water. If white cotton starts to appear, switch to fungal treatment

Heater burns

PreventionFit a heater guard. Eliminate gaps where fish can get trapped. Use a heater with dry-run protection

First aidWhite discoloration or peeling at the site. Isolate, keep water clean, and do small daily water changes to prevent infection

Temperature shock

PreventionAlways use water of the same temperature for changes. When introducing fish, float the bag for 30 minutes and mix water in gradually

First aidIf lying on its side and motionless, return the temperature to normal and keep it dark and quiet. Increase aeration and watch without touching

Nontuberculous mycobacterial infection (fish tank granuloma)

RouteThrough cuts on hands that touched tank water or fish

PreventionWear rubber gloves if you have cuts on your hands. Wash with soap after tank work

Salmonellosis

RouteHand to mouth after touching tank water, filter media, or gravel

PreventionDo not pour tank water down the kitchen sink. Always wash hands after tank work

Aeromonas infection

RouteDirty tank water entering wounds, eyes, or mouth

PreventionDo not siphon water by mouth. See a doctor if a wound swells

Anisakiasis

RouteEating ornamental fish raw (normally never happens)

PreventionDo not eat ornamental fish. Do not handle frozen bloodworms with bare hands

Food

• Commercial fish food as the staple. 1–2 times a day, an amount eaten within 2–3 minutes
• Frozen bloodworms and brine shrimp as treats 1–2 times a week
• Fasting for several days while you travel is fine. Set automatic feeders to a small amount

Water

• Dechlorinate tap water with a conditioner and match the temperature before adding
• Change 1/3 of the water once a week. Avoid full water changes, which kill the filter bacteria

Toys & play

• Create swimming space and hiding spots with plants and driftwood
• For bettas, place floating plants or a leaf-shaped resting spot near the surface
• Do not chase them with a mirror or your finger (severe stress)

Nest, bed & hideout

• Clay pipes, driftwood, or dense plants to hide in, one per fish
• For bubble-nesting bettas, keep the current gentle

Bedding & litter

• A thin layer of smooth gravel or sand; siphon out waste at water changes
• A bare-bottom tank (no substrate) is easy to clean and suited to isolating sick fish
• Remove waste and leftover food from the bottom daily with a pipette

Cage / housing material

Glass or acrylic aquarium. A lid, filter, heater, and thermometer are essential

Size & space

At least 10 L per goldfish; for small tropical fish, 5–10 fish in a 30 cm tank as a guide

Layout

• Aim the filter outflow so it ripples the surface and draws in oxygen
• Place the heater where there is current to avoid uneven temperature
• Provide both hiding spots and open swimming space

Placement notes

• A windowsill with direct sun causes temperature rise and algae
• Place on a level, sturdy stand. A 60 cm tank weighs over 70 kg in total

Exercise, free-roam & walks

• No walks needed. Provide enough room to swim naturally in the tank
• Observe every fish's swimming and body surface once a day
• Keep catching and moving to a minimum. Do not chase with a net

Temperature & humidity

TemperatureTropical fish 25–28°C; goldfish and medaka 15–28°C. No more than 2°C change per day

HumidityNot applicable underwater. Use a lid to limit evaporation and jumping

Summer & winter

• Summer: keep below 30°C with a cooling fan or air conditioning. Aerate to prevent oxygen shortage
• Winter: heater essential. Outdoor medaka can overwinter at the bottom even if ice forms

Nail trimming

No nail trimming. Instead, the most important care is a weekly water test (nitrite, pH) and water change

Brushing, skin & coat care

No coat care. To protect the slime coat, do not touch; use a soft, fine-mesh net

Other care

Rinse filter media in tank water (tap water kills the bacteria). Scrape algae off the glass at water changes

Protection from predators

• Use a heavy lid so cats cannot reach into the tank
• Outdoors, use netting against herons, crows, dragonfly larvae, and cats
• Keep fish in outdoor containers and manage them so they do not breed mosquitoes

Foreign-body ingestion

Fish can swallow small gravel or oversized food and choke. Choose food pellets sized for the mouth and smooth substrate

Being stepped on

No risk of being stepped on in the tank, but check the floor every time you work so you do not step on a fish that jumped out

Getting pinched

Fish get trapped at heaters, filter intakes, and gaps in the layout. Fit sponge covers and avoid creating narrow gaps

Falls

The tank itself tipping or falling is the worst accident. Place it on a stable dedicated stand with an anti-seismic mat for earthquakes

Escape

Jumping out = escape. Always use a lid and block cord holes. If found on the floor, return it to water even if dry and watch for several hours

Safe release procedure

1. Separate fighting fish with a divider, not a net
2. Immediately isolate the one being chased in a separate container
3. Male bettas are kept alone for life. Never house them together
4. After a fight, keep the water clean and wait for the fins to regrow

After the release

Torn fins regrow naturally in clean water. If white cotton or red hemorrhagic spots appear, switch to disease treatment

What to tell the vet & what to bring

Tank size, number of fish, water temperature, water change frequency, test results, medications used. Bring the fish in a bag of tank water

Checking consciousness, breathing & heartbeat

• Are the gills moving? (normal is roughly 60–120 per minute)
• Does it flee when you bring a finger close? Do the eyes move?
• Even on its side, if the gills move there is a chance of recovery

Stopping bleeding

• Fin bleeding stops on its own in clean water
• Add slime-coat protectant at the labeled dose and use a 0.5% salt bath to prevent infection
• If bleeding from the body continues, see a vet who treats fish

Transport

• Put plenty of air in a bag or container with tank water
• Place in a foam box to hold temperature, keep dark, and carry without shaking