By Donna M. Recktenwalt
Many a killikeeper has learned to his regret that many killifish not only will jump, but even seem to want to jump. They are now firm believers in the rule that “if they can jump out, they will,” and its corollary: “even if they can’t jump out, they will.” Leave a killie tank uncovered and you are almost certain to find dead fish on the floor; leave even a gap for some species, and your chances of having “crispy critters” are high.
But why do fish jump?
For defense. In nature, some fish jump as an instinctual evasive maneuver. In aquaria, being startled, whether by sudden movement or abruptly turning on the lights, will often trigger this jumping response.
For reproduction. Although the behavior has not been specifically observed in killifish, some fish have adapted to laying their eggs out of the water, on the underside of a convenient leaf, or in mud above the waterline
To some extent, , the tendency to jump seems to be genus-related. “In my experience with annuals,” observes Eric Lund, “jumping capability seems to be pretty much (but not entirely) genus-specific. I tend to keep open-topped tanks with non-jumpers and almost never lose a fish to the floor.” In Eric’s experience, the non-jumpers include: Nothobranchius, Cynolebias, Terranatos, Fundulopanchax filamentosum and F. walkeri. Jumpers include Fundulopanchax (F. occidentalis is the champ, “Give them a hole and a day and I’ll show you a fish chip,” says Eric) and Pterolebias.
“I have had C. bokermanni jump,” Oleg Kiselev says, “but otherwise I agree [with Eric Lund’s observation]; Cynolebias are not jumpy.” However, regarding F. filamentosum and F. walkeri, “in my experience both these species will jump if given a chance. I’d go so far as to say that all Aphyosemion and Fundulopanchax species are jumpers and their tanks should be tightly sealed. The same goes for all Moema, Pterolebias and Rivulus species. They are all jumpers.”
Some of the Rivuluns take the jumping behavior even farther, voluntarily spending considerable periods of time out of the water, lying in wet leaves or mud. In aquaria, they hang from the sides of the tank above the waterline, or from the tank cover. Aquarists have even observed these fish lying on top of floating spawning mops. Eventually, they will flip back into the water.
“My experience is that killies are more likely to jump if they are new to a tank/fishroom,” observes Donald Nute. “Still, I had a large breeding group of A. bitaeniatum for three years in a 30 gallon tank, and every time I left the tank open for half an hour I would find two or three on the floor. One thing seems certain: other things being equal, the likelihood that a killie will jump is directly proportional to its desirability and inversely proportional to the ease of replacing it. In other words, the better you like it and the harder it is to replace, the more likely it is to jump.”
Other factors that can trigger killies to jump include bare tanks, which can lead to nervous fish and high stress levels; fright syndrome; and deteriorating water conditions. To ease stress levels of the fish, try adding more cover in the form of plants or mops; additional security in the form of dark paper or cardboard dividers between adjoining tanks; some gravel or peat on the bottom to hide the glass; or “dither fish” such as guppies or Heterandria formosa. Peat has the added benefit of absorbing excess chemicals from the water, including those produced by panicked fish, thus also easing the effects of fright syndrome. Reducing light levels may help, too.
Regular water changes, of course, are the answer to poor water conditions, but the addition of carbon or a cube of the new polyfilter to the filtering system can also help.
— G.C.K.A. Newsletter, Sept/Oct 1998