WHY DO FISH JUMP OUT OF OUR AQUARIUMS?

 

 Notorious jumper - the longnosed hawkfish. 

 I had a fish jumping incident happen recently that was difficult to comprehend. A Reef Tectonics client had a longnose hawkfish (Oxycirrhites typus) that had been in his aquarium for over a year. It was a “happy” fish that seemed to live a copacetic life with its tankmates. While working on the tank, I broke a small portion of the glass top (this resulted in an opening about four by three inches in the front portion of the cover). Before I could replace the top, the hawkfish was found dried up on the office floor – it had jumped out. I was perplexed as to why the fish jumped and how the fish was able to detect the hole in the top that had not been there for its first year in the aquarium?

Some fishes that are well known for jumping out of aquariums include: morays, snake eels, garden eels, anthias, hawkfishes (especially the longnose hawkfish), jawfishes, tilefishes, wrasses, sand perches, gobies and dartfishes. Morays are by far the worst jumpers. These fish will push their head from the water as they swim along the water’s surface and appear to test the top for openings. If there is an aperture, they are likely to find it and slither out of the tank. Not only will they leap from an open tank, large eels will occasionally push off aquarium tops to facilitate escape. In the case of these animals it may be necessary to place weights on the top to prevent this from happening (of course, make sure the weights you use are not so heavy that they break the glass – I use two pound weights for a diving weight belt). Morays apparently slither out of their aquarium home as they search for happier hunting grounds.

Some other renowned jumpers include certain wrasses, especially the fairy wrasses. A late friend, Bill Gordy, had an extra-large tank with numerous fairy wrasses. On several occasions, he had fairy wrasses leap from the tank when he removed the glass top and turned to clean it in a nearby sink. On his way back to the tank with the cover, he would find a fairy wrasse or two flopping around on the floor! Obviously, the wrasses were able to perceive (see) when the top was removed and they would then begin their aerial antics. Why? Who knows! Maybe they couldn’t stand the aquarium décor? It is true that male fairy wrasses tend to jump out of aquariums more often than females because they engage in a vertical swimming display that often results in their propelling themselves against the glass top or out of the tank if a top is not present. Male fairy wrasses have also been known to collide with and break metal halide lamps when they jump.  

Jawfishes also regularly leap from aquariums. Like many other leapers they are experts at finding the smallest opening in the aquarium top to jump through. In most cases, jumping occurs before they find an appropriate location in the aquarium to dig their burrow. This is often during their first night of captivity. It is a good idea to leave the light on (that is, if it does not contain live corals) until the jawfish is able to create a suitable burrow.

A lot of fish jumping occurs after dark. This is probably a result of the quiescent fish being startled by another organism in the tank. In an attempt to escape, the fish races vertically up into the water column. The problem is, they are in a glass box not in the ocean! They end up hurtling out of the tank and onto the carpet. Many have employed a small night light over the tank to help reduce the possibility of jumping. Another time when fish are likely to leap from their glass home is when they are being incessantly attacked by aggressive tankmates. If you have a potential leaper that is being picked on, you are going to find that fish on the floor if there is any way for it to leap from the tank.

Not only do fish leap from tanks, they sometimes leap into overflow boxes. If you have an overflow box built into the corner of your aquarium, make sure it holds two or three inches of water so that these fish can survive until you find  and remove them.

© Scott W. Michael- Reef Tectonics

Reef Tectonics Aquarium Maintenance and Design - Lincoln, Omaha, Des Moines, Kansas City