By Donna M. Recktenwalt
Although the annual and semi-annual killifishesthe Nothobranchius of Africa and the Cynolebias of South America, as well as some of the Fundulopanchax species, and otherscontain some of the most beautiful and interesting members of the killifish kingdom, they are also among the most challenging to breed, given their substrate spawning behaviors and the need for their eggs to go through a sometimes extended incubation period. But the beauty and the fascinating reproductive behaviors of the annual and semi-annual fishes are reasons enough to accept the challenges of keeping them.
Of course you supply the preferred water and temperature conditions for the species, and you properly condition the breeding fish. But what do you use for a spawning medium? How do you know if you have eggs? And then what is the best way to store those eggs for the required diapause period?
Although peat is the usual substrate of choice for annual and semi-annual species, some breeders have been highly successful using other media in its placefine glass beads, greensand, or bottom mops.
Peat moss comes in several forms and varieties.
Canadian Sphagnum peat (nursery grade) may be purchased by the bale at your local garden store, usually wrapped in plastic. It may contain fine rootlets, twigs, and other solid matter, but some species seem to prefer this roughage.
Compressed peat pellets, the “gourmet” approach for smaller amounts, are more uniform and wet well. The resulting peat is quite fine from the #703 pellets, and somewhat coarser from “Gro Brix.” Be certain to purchase the pellets without additives.
Finally, there is “New Zealand” peat. This product appears more like dried java moss, and is very fibrous, with very little particulate matter.
Al Anderson, who has bred a number of “divers”, suggests running regular peat through a blender to create“super-fine peat”. Although this extremely fine material will cause clouding in the spawning tank, it’s easy to harvest the eggs by rinsing the peat through a fine net or sieve.
Whatever type of peat you use, it must first be boiled and cooled. For small amounts this may be effectively accomplished in a microwave; for larger amounts, a non-metal pan on the stove will do the job. Try to schedule the task on a day when you can have the doors open, or when the rest of the family will be elsewhere. Boiling peat has a distinctiveand to some, unpleasantodor.
There are several recommendations for storing prepared peat. One method recequires squeezing out the excess water, then storing at room temperature in a sealed glass jar or in the refrigerator in a plastic bag .For larger amounts, store peat in water in a 5-gallon pail with a small hex undergravel filter running. Wet peat in still water will rapidly turn sour.
Greensand (or “green marl”) is a fine sand/clay blend of dusts released by glacial ice melt. It may (or may not) be available from garden stores or hydroponic suppliers. Since greensand is in part fine clay silt, it easily clouds tank water, and the rough edged sand grains can cause abrasion damage. To use, place about 3/4″ in the bottom of a container. To harvest the eggs, fill another dish with clear water, set a fine sieve on top of it, and gently wash the greensand through the sieve.
Fine glass beads are used for polishing, cleaning and deburring, and sandblasting. Coated with reflective material, they are used for road signs and the reflective stripes on roads. They make a good spawning medium, since they have no rough edges and will damage neither fish nor spawn. Place the beads in a small square container and locate in the darkest corner of the tank. To harvest, stir the beads gently in a circular motion. The eggs will rise and gather near the center.
Spawning mops are a traditional killifish standby, used to both to provide cover for the fish and as a site for spawning. Although traditionally used for plant spawners, mops can be used for diving and plowering spawners as well.
Wright Huntly reports that he has successfully spawned diving species in mop-filled pots slightly taller than the length of the male fish. He notes that you may need to train the fish for a couple of weeks, using peat beneath the mops, but the fish will learn to use them. As Derek Fairbrother points out, “collecting [the eggs] is very simple. All you do is pull the container out, leaving a bit of water … then run the yarn through your hands slowly. Because most of the eggs for powers and divers aren’t very “sticky”, the eggs simply fall into the water.” For fish that like a deep bed to dive into when they spawn, try using mops or a thick layer of sphagnum moss on top of the peat. The fish will seek and spawn in the peat; the mops or sphagnum layer will help prevent spillage, and keep the fish from finding and eating their own eggs.
Whatever medium you choose, most breeders agree that confining the spawning material to a container of some sort is usually preferable to having it loose on the bottom of a tank. Plastic containers work well, but often must be weighted with marbles or small stones to keep them on the bottom. A better answer, suggests Ted Klotz, is glass containers with screw lids. These are particularly effective for media that tends to cloud the water. Select an appropriately sized jar, add the media of choice, then fill to the top with water and screw on the lid. Place the whole container in the spawning tank. When the spawning media has settled, carefully unscrew and remove the lid. To collect the spawning material, carefully screw the lid back on and then remove the jar. This procedure eliminates spillage, and the weight of the jar itself keeps it firmly on the bottom.
To reduce peat spillage, Steve Halbasch suggests putting peat into a rectangular container and partially filling it with water, then covering the entire container with a “sleeve” cut from old pantyhose . With the “sleeve” in place, gently introduce the container into the tank. An hour or so later, when the peat has settled, slide the “sleeve” partway back. The fish often will spawn beneath the covered side of the bowl. When it’s time to remove the peat, simply slide the “sleeve” back into place and carefully lift the container from the tank. — G.C.K.A. Newsletter, June 1997