At one time or another, almost every killifish breeder has encountered a pair of fish that he or she simply cannot get spawn or fry from. However, notes Mike Wilson, the aquarist can make a number of common changes that may trigger spawning in reluctant breeders. The following are a few examples.
Change things in the tank. Move mops, add a mop or two, change the location of substrate containers or filters, add or subtract plants, etc.
Change the water- part or all of it. Some species will respond well to small, daily water changes. Others will begin spawning in earnest only when the water changes are suspended for a few weeks.
Add some boiled fibrous peat (New Zealand sphagnum).
Substantially lower the water level. Be certain that there is at least an inch of water above the top of the spawning container, and leave the water level low for about 24 hours. Breeding often will increase. Be certain to add additional hiding places for the females. If the females have mature eggs, they will find the males.
Move the breeders. A new environment can start or stop breeding. Plan to breed the fish immediately upon moving them; moving older breeders can be risky, especially for annual fish, triggering rapid aging and death.
Use controlled spawning. Separate the breeders and unite them only for brief spawning periods. Be sure to provide hiding places for the females, and to monitor the spawning closely, since males are often very aggressive.
Change the air or water flow.
Add a mirror to the side of the tank. Fish often respond strongly to the presence of “other fish” and egg production will increase. Be alert to increased male aggression and add extra cover for the females.
Try group spawning. Results are not always as good with groups as with pairs, but this is still worth a try. In group settings it is usually the females that initiate spawning.
Change the feeding regimen. Increase it, decrease it, change the times or the quantities. Fish that are heavily fed with quality foods often are less aggressive. Remember that heavier feeding means more water changes. Make sure that all females get enough food. Males and dominant females may monopolize the food source.
Change the temperature..
Check the spawning mops at various times. Check mops three times a day to determine when the fish are actually breeding. Different species (and even different pairs of the same species) can surprise you. Collecting eggs at different times can also break the cycle of spawning followed by egg eating.
Try a mixture of peats. Even some of the peat spawners have been known to search for and eat their own eggs. Try a deeper substrate, a mix of fibrous and non-fibrous peat, bottom mops atop the peat, or an alternate substrate material entirely – fine glass beads, greensand, or bottom mops alone. GCKA Newsletter, October 1997