By Donna M. Recktenwalt
One of the most useful tools that killifish breeders have at their disposal is peat moss. We use it as a pH buffer, as a spawning medium, and as a substrate. However, many aquarists have found that it has another use: as an incubation medium for the eggs of many plant- or mop-spawning non-annual species.
“I hardly ever water incubate eggs,” says Geert van Huijgevoort, “especially with species like Fundulopanchax amieti or F. puerzli, that need a longer incubation period.” Even with frequent water changes, he points out that iti is nearly impossible to prevent fungus from wiping out all or most of the eggs. “By far, the best way for me to incubate eggs, whether they are from Aphyosemion, Fundulopanchax, Epiplatys, or Rivulus, is to put them on top of boiled or microwaved peat.”
In a petri dish or plastic container (small butter or margarine tub) with a tight lid, place a layer of peat moss that has been boiled, drained through a net and squeezed until no more water runs out. To this add water from the tank where you are harvesting the eggs, or your favorite hatching water mix. Allow the peat to soak, then pour out excess standing water.
Eggs should be placed on top of this peat without touching each other, the container covered and kept in the dark. The first week or so, check every few days and remove any unfertilized or fungused eggs. After that, check weekly to make certain there is sufficient moisutre, adding water as required.
At the same time, check for eye development. The eggs are ready to hatch when a nice gold ring is visible around the eye. Some eggs will even show movement of the embryo when stimulated by a bright light.
When the peat is wet (flooded with water) after the incubation period, all fry usually hatch within one or two days, so eggs laid over the period of a week or two can be hatched together. Any laggards can be “encouraged” by using any of the proven methods for forced hatching.
“On peat there seems to be some leeway on hatching time,” says Mike Reid. His students use damp peat to incubate F. gardneri, and have found that it can double the incubation times. A. australe eggs usually take three weeks to hatch, but that time can be extended to six. The technique has also been proven with A. cameronense, A. striatum, and others.
There is a downside to the peat technique, however. “Sometimes I find little hatchlings dead on the peat,” says Geert, “especially with my Chromaphyosemions,” which lay eggs that sometimes hatch after nine instead of the usual twelve days.
A variation of this incubation technique is to use clean paper towels wet with your favorite hatching solution; this may not always work, but may be worth a try if you’re having problems with hatches.
– G.C.K.A. Newsletter, February 1999