By Donna M. Recktenwalt
Even the best and most experienced killikeepers occasionally have problems with eggs and fry. The “proper way” to incubate and hatch out killifish eggs varies, of course, with the species, their spawning habits, their incubation requirements, and the preferred techniques and proven methods of the fishkeeper.
“[Water incubated] eggs, if they are viable, will do their thing,” says Charles Harrison. But sometimes, they need a little assistance. Between spawning and hatching, all eggs are under threat. They may be eaten. They may fungus. They may hatch prematurely. Or they may simply disintegrate entirely, leaving no trace.
“If [eggs] don’t develop and hatch in a timely fashion, they will disintegrate,” Lee Harper says, discussing his experiences with Aphyosemion sjoestedti. “I collect eggs from the gravel and watch them for a few days in water. If they seem to be still alive after several days (i.e. they don’t fungus or disintegrate), I then put them on or in peat. If I want to be able to count them or watch them I put them on top of damp peat. If I don’t care I just mix them into damp peat and incubate for 6 to 10 weeks. Sometimes they don’t hatch … even though they seem viable at first.”
“I never keep my [killie] eggs in tank water for fear of a higher bacteria count, which might destroy the shells and cause premature hatching,” says Jeff Bilbrough. In premature hatching, eggs die as their shells rupture. This can happen early in the development of the embryo, where it is seen ‘oozing’ out of the shell, or at subsequent stages, leaving an incompletely developed, unprotected embryo that soon dies. In the latter stages, the tail punctures the egg membrane, but the remaining part of the embryo can’t free itself.
“I do use methylene blue,” Jeff continues, “but only for the first three days to determine unfertilized eggs; they’ll turn dark blue.” He changes water in the hatching container daily, adding a few grains of Jungle brand Binox. “I’ve [also] begun sterilizing my hatch containers with weak Clorox and drying them for a few days before using them,” he says. “Since I’ve started these procedures I seldom have premature hatching and fry dying young.”
“What has worked to a degree [for premature hatching] is changing the hatch water every few days,” reports Howard Berg. “If the fry are already prematurely out of their shell I have been able to save some by changing the hatch water every day until they have used their yolk sack and become free swimming.”
Al Anderson increases the general water hardness by adding a teaspoon of well water to each 6 oz. of hatch water. “Most of the time this works,” he says.
“Keep the water that the eggs are in as clean as you can, says Charles Harrison. “Change it every few hours if you can. Pour the eggs through a Brine Shrimp net, rinse out the hatching dish, replace the eggs/fry and keep it all clean and fresh. … The best containers are the flat bottomed ones so the eggs don’t slide together and get involved with fungus, etc.”
When eggs handled in any way are dying off, then not handling them at all is a useful strategy.
Having several breeding tanks ready offers another solution; when the adults have spawned in the first tank for two weeks they are simply moved to the next and the eggs allowed to incubate unmolested. Alternatively, you can remove the mops or peat to another container for hatching. If you have spawned your fish over gravel (especially in a tank with an undergravel filter) the regular circulation in the tank can often provide sufficient aeration for the eggs.
If one method doesn’t work for you, try another. Keep in mind, too, that not all breeding fish will always produce viable spawn. Some species are notorious for infertile eggs when young, with fertility increasing as the fish age. In other cases, a pair may be fertile for a time, then cease producing eggs altogether for a while.
— G.C.K.A. Newsletter, January 1999