By Donna M. Recktenwalt
Breeding and raising species of the annual and semi-annual killifishes is a challenge for the aquarist, given their substrate spawning behavior and the subsequent storage period required by the eggs. In a previous article, we focused on the spawning media available for use by the aquarist. In this article, we assume that you have observed your annual or semi-annual fish successfully spawning.
But can you prove it by finding the eggs?
This is hardly a minor question. Actually seeing newly laid eggs can prove whether you actually have eggs to store. Later on, seeing eyed up eggs can help evaluate whether the peat is ready to wet.
Seeing even small eggs that have been freshly rinsed from clean spawning mediabe it greensand, glass beads, walnut shells, sphagnum moss or mopsis not terribly difficult, no matter the egg size. Eggs vary from the very small to the very large; from clear (transparent) to a pale amber when freshly laid.
Seeing the eggs after storage in peat, however, takes practice, since no matter their color when laid, the eggs soon become stained a dark, dull brown.
“In my opinion,” says Andrew Broome of New Zealand, “the only definite way to check for eggs in peat is to do it as soon as the peat is harvested. I figure that I can spot about 10% of the at that stage clear eggs.” For spotting eggs, Andrew uses overhead or side lighting, and manipulates the peat in its storage bag while looking through the open top.
Jay Exner suggests using a backlight and “getting the eggs ([on] spawning mops, plants, whatever) between your eyes and a bright light. You will see bright dots for new eggs (i.e., the optical effects of light being refracted through spherical lenses.” This works for peat if you can spread it out on glass with a light behind itin a glass or clear plastic baking dish, for example.
“I’m far older and have poorer vision than most,” observes Wright Huntley, “but if I can find Cynolebias fluminensis eggs [in peat] when ripe, you can find them.” His tips?
Use magnification to help youa jeweler’s loupe or a hand-held magnifying glass.
Use a bright desk lamp (Halogen is particularly good) positioned directly across from you.
Use a white-bottomed container, and spread the peat thin. Sometimes light reflected from the bowl beneath will shine through the eggs.
Fluff the peat, then pat it down to a fairly smooth surface. Scan over it, using your magnifier, with the lamp only a couple of feet from the surface.
No luck?
Lay a paper towel over the whole mass of peat and flip it over to look at the other side. Refluff and repeat this procedure a couple of times.
As a last resort, start at one edge of the peat and slowly separate it into “examined” and “unexamined” portions, with a gap between, using tweezers or a similar tool to move the shreds of peat fiber from one pile to the other.
With luck, you’ll find eggs in that newly harvested peat and can put it into storage with confidence.
Storing the Eggs
The fish have spawned. You’ve collected the spawning media and checked it for eggs. You’re ready to put the eggs away for the recommended incubation period.
But what media do you use to store those eggs, and into what do you put that material?
The nearly unanimous answer regarding the proper storage medium for incubating annual or semi-annual eggs is slightly moist, crumbled peat. It’s acidic nature helps keep bacteria growth to a minimum and helps prevent eggs from fungusing. The eggs are also effectively separated from each other so that any that do go bad don’t infect the rest.
If the eggs were spawned over peat, simply dry the spawning medium to the proper degree of moistness before storage, using paper towels or newspaper to wick away the excess moisture. If spawning was accomplished over another medium, place the eggs into the slightly damp peat and mix it before drying, to achieve an effective distribution.
By far, the consensus regarding the proper storage container for egg-laden peat is plastic bags. These may be either standard plastic fish bags, or plastic freezer bags. Both are fairly permeable to the small molecules of oxygen, but impermeable to the much larger water molecues, which means that developing eggs get sufficient oxygen without the risk of drying out. Place the egg bearing peat into a plastic bag, seal the bag, and mark it properly as to species and spawning date.
More tightly sealed containers, such as plastic petrie dishes sealed with electrician’s or similar tape, have proven acceptable for eggs that undergo only a short diapause (4 weeks or so). For eggs that require longer storage they are a poor choice, due to their impermeability to oxygen.
Once the eggs are safely in their storage container, look up the appropriate incubation period based on the temperature conditions in your fishroom, and mark down the anticipated hatch date on your calendar, on the bag itself, or on index cards filed by month.
Now put the bag of resting eggs away.
From now on it’s just a matter of time. All you have to do is … wait.
— GCK Newsletter, October 1997