Cat in fish tank? Keeping cats, dogs and kids safe around aquariums

If your cat is fishing in your tank, the fix is a strong, close-fitting lid that a cat cannot lift or fall through. Most problems with cats, dogs and young children come down to three things: an open top, a tank that can be knocked or pulled, and food or chemicals getting into the water.

If a cat has just been in the tank, check your fish for injuries and wipe up any spilled water now. Then work through the steps below to make the tank pet-proof and child-proof for good.

What you need

A solid, close-fitting lid (glass or rigid plastic), ideally hinged and with a clip or weight
A sturdy stand rated for the full weight of the tank. Water weighs about 1 kg per litre (8.3 lb per US gallon)
Furniture straps or anti-tip brackets for tall stands
A cable organiser and drip loops for all power cords
A lockable box or high shelf for fish food and treatments
Pre-portioned food: a weekly pill organiser works well

Step by step

If a cat or dog has just been in the tank

Get the animal away and close the room.
Count your fish and look for scale loss, torn fins or wounds. Check behind and under the tank for any fish that were flicked out. See jumping for fish found out of water.
Turn off power if water spilled onto cords or sockets. See electrical safety.
Put back any knocked-over decor carefully. Check that rocks are not resting on fish or pinning the heater against the glass.
Test the water over the next day or two. A cat's paw or a dog's tongue can carry flea treatment, shampoo or dirt into the tank.
Watch injured fish for signs of infection, such as fuzzy or red patches, over the next week. See fin rot and fungus.

Cats

Lids are the answer. Mesh or hinged flaps can bend under a cat's weight. Use glass or rigid plastic, cut to cover every gap, with filter and heater cut-outs as small as possible.
Weight or clip the lid. Clever cats learn to lift light lids. A clip, latch or a weight on the lid stops this.
Remove the launch pad. Cats sit on the lid because it is warm under the lights. Don't put a shelf or chair next to the tank.
Distract and redirect. A window perch or bird-watching spot elsewhere gives your cat something better to watch.
Open-top and shallow tanks (like paludariums and bowls) are best kept in rooms the cat can't get into.

Dogs

Big dogs can bump or lean on a tank, and wagging tails can knock things off low stands.
Put tanks on solid stands, against a wall, out of busy walkways.
Keep cords tidy and out of chewing reach.
Don't let dogs drink from the tank. Aquarium water can carry bacteria, and fish medicines may be harmful to them.

Children

Anchor tall stands to the wall. A full tank is very heavy and dangerous if a climbing child pulls it over.
Keep lids closed and clipped so small hands can't drop toys, snacks or soap in. See soap and chemicals.
Stop tapping. Explain that tapping the glass scares the fish. A step stool and a "look, don't touch" rule help.
Keep electrics out of reach, with drip loops and a safety switch (GFCI or RCD). See electrical safety.
Glass and heaters: keep hammers, toys and stones away from the glass. See cracked tank.

Kids overfeeding

Children love feeding fish, and that often means the whole pot goes in. Too much food rots, causing ammonia spikes and cloudy water. See overfeeding and cloudy water.

Hide the main food pot in a high cupboard or a lockable box.
Pre-portion the food. Put one meal in each section of a weekly pill box. Your child gets to feed, but only the right amount.
Use a feeding chart on the fridge so nobody feeds twice.
If the whole pot went in: net or siphon out as much food as you can right away, do a 30–50% water change, and test ammonia daily for a few days.

Flea treatments, sprays and essential oils

Many pet flea and tick products contain insecticides that are highly toxic to fish and shrimp, even in tiny amounts. Permethrin, common in dog products, is a well-known example. It is also dangerous to cats.

Apply spot-on treatments, sprays and shampoos well away from the tank, ideally in another room.
Wash your hands thoroughly before touching the tank, and wear gloves for tank work for a day or two after handling a treated pet.
Keep treated pets away from the tank until the product has fully dried, and stop them drinking from it.
Never pour rinse water from a pet bath near the tank or into the drain you use for aquarium water.
Avoid flea bombs, fly sprays, air fresheners, aerosol cleaners and essential-oil diffusers in the fish room. Air pumps pull room air into the tank. If you must use an insect fogger, cover the tank, turn off air pumps and ask your vet or the product maker for advice.
Ask your vet about pet treatments that pose less risk to fish if you have aquariums.

If fish start gasping, flashing or dying soon after a pet treatment or spray, do a large water change, add fresh activated carbon to the filter, and see our soap and chemicals guide.

Common mistakes

Using a mesh or flimsy lid that a cat can push through.
Leaving the food pot where children can reach it.
Spraying flea or bug products in the same room as the tank.
Placing a tank on a low table in a hallway or play area.
Assuming an aquarium is safe because "the cat has never bothered it". Cats learn.

Products that help

Glass or rigid acrylic lid with clips: the best single fix for cats and curious kids.
Furniture anti-tip straps: stop tall stands from being pulled over.
Weekly pill organiser: pre-portions fish food for children or pet sitters.
Lockable storage box: keeps food and medicines out of reach.
GFCI or RCD safety socket: cuts power if water reaches the electrics.
Activated carbon: helps remove chemical contamination after an accident.
Liquid water test kit: checks for ammonia after overfeeding.

How to prevent it

Plan the tank's location before you set it up: solid stand, against a wall, away from cat launch spots and busy walkways.
Always use a secure lid.
Store food, medicines and pet treatments separately and out of reach.
Make one adult responsible for feeding, or use pre-portioned meals. See vacation for pet sitters.

Why it happens

Cats are natural hunters, and fish moving in a warm, bright box are irresistible. Dogs and children are curious and bump into things. Most accidents happen because the tank was easy to reach, easy to open, or near chemicals.

When to get help

See a vet straight away if your cat has been treated with, or has licked, a flea product made for dogs, or if any pet shows drooling, tremors, weakness or seizures after a treatment. Permethrin poisoning in cats is an emergency. See an aquatic vet or experienced fish shop if fish keep dying after a chemical exposure, or have deep wounds after a cat attack.

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