Fish That Jump Out of Aquariums

Almost any fish can jump. Some make a habit of it.

Ask around a reef club and nearly everyone has found a fish on the carpet, usually one they never expected to jump. Fish leave the water for a few reasons: they are startled, they are being chased, they are hunting something at the surface, water conditions have gone wrong, or, for a few species, because leaping is simply what they do. Most of it happens at night, often in the first week after a new fish is added, and a gap the width of a power cord is enough.

The lists below are the species that come up again and again. If you keep one of them in an open-topped tank, it is a matter of time.

Saltwater fish that jump

Wrasses: fairy and flasher wrasses, six-line, melanurus, leopard and Christmas wrasses, and the cleaner wrasse. Wrasses are the number one jumper in the reef hobby. They bolt when startled and go straight up.
Firefish and dartfish: purple, red and helfrichi firefish, scissortail and zebra dartfish. Nervous, fast and famous for leaving through the smallest gap, usually at night.
Gobies: watchman gobies, clown gobies, neon gobies and especially the sleeper and dragon gobies. Many are escape artists even when they look like they sit still all day.
Jawfish: the pearly jawfish is known for jumping when disturbed or when its burrow collapses.
Blennies: tailspot, midas, lawnmower and bicolor blennies climb and jump, particularly at night.
Hawkfish: perch high on the rock and launch when startled.
Anthias and chromis: schooling fish that scatter and jump when chased or spooked.
Dottybacks and basslets: the royal gramma and orchid dottyback jump less often, but it happens, especially during aggression.
Clownfish: not a habitual jumper, but a startled clown goes over the edge often enough that a lid is standard advice for the Fluval Evo and Waterbox Cube tanks they usually live in.

Freshwater fish that jump

Bettas: more than any other freshwater fish, bettas leave rimless desktop tanks, usually at night or when the water is off.
Killifish: nearly every species, which is why killifish keepers run tight-fitting lids as a rule.
Hatchetfish: a surface fish that leaps for insects in the wild and keeps doing it in a tank.
Danios, rasboras and tetras: zebra and giant danios in particular, often at feeding time or when the lights go out.
Rainbowfish and barbs: active schooling fish that jump when chased.
Livebearers: swordtails, mollies and platies, usually during courtship chases.
Loaches and eels: kuhli loaches, hillstream loaches, spiny eels and peacock eels find any gap at the back of the tank, especially around filter intakes.
Gouramis and paradise fish: surface breathers that occasionally go over.
African and Central American cichlids: jump during fights and spawning.
Arowana, knife fish and other large fish: strong jumpers that need a lid they cannot lift.
Shrimp and snails: Amano shrimp and nerite snails do not jump, but they climb out along cords, hoses and the glass wherever the top is open.

Why fish jump

Startled: the lights go off, a door slams, someone walks past, a hand goes in the tank. Night is when most losses happen.
Chased: a new fish, a pair squabble, a spawning run.
Water problems: ammonia or nitrite in a new tank, low oxygen in a warm one, a pH or salinity swing after a top-off mistake. A fish that keeps jumping is often telling you something about the water.
Hunting and instinct: surface feeders leap for food, and some species (wrasses, killifish, hatchetfish) jump in the wild to escape predators or move between pools.
Flow and surface agitation: a return nozzle or a wavemaker aimed at the surface can carry a small fish over the edge.

Closing the gaps

A lid stops jumpers only if there is nowhere to go. The three places fish get out are the corners, the equipment gaps at the back where cords, hoses and brackets cross the glass, and the feeding gap left when a lid is propped open or set aside.

Use a lid that sits inside the glass on a lip rather than one that rests on top of the rim. A frame on the rim leaves a slot along every edge; a lip inside the glass closes it.
Give each cord and hose its own cutout sized to it, rather than leaving one big gap at the back. Measuring a cutout takes a minute.
Feed through a capped feeding hole so the lid never has to come off at feeding time, which is exactly when fish are excited and near the surface.
Keep gas exchange. A sealed top solves jumping and creates a different problem; a mesh window keeps fish in while the tank breathes.
On an all-in-one tank, the lid covers the display and stops at the filter chamber; keep the factory chamber covers on so the back section is closed too.

⚠️A new wrasse, firefish or goby should go into a covered tank from day one. The first nights in a new home are when most jumpers are lost, and they will not wait for the lid you were going to order next week.

Lids for the tanks these fish usually live in

The nano reefs that hold a clown pair, a goby and a firefish are the tanks we cut the most lids for: the Fluval Evo 13.5, the Waterbox Cube 20, the Innovative Marine Fusion 20, the Red Sea Max Nano G2 and the JBJ Nano RL 20 among them. Planted and shrimp tanks from UNS, Landen and Waterbox are covered the same way, as a full-top lid that sits inside the glass. Every lid is cut to the model with a feeding hole and cutouts where you want them; find your tank to see it drawn.