by David Schaeffer
Last time, we discussed Fundulopanchax gardneri N’sukka. This fish is very often the fledgling killie-keeper’s intro to the world of killifish breeding. It is attractive, hardy, easily bred, and readily available, but there are many other types of killie that also fit that description. One of the best is Cynolebias (Nematolebias) whitei.
The name in parentheses reflects the fact that this fish has undergone a name revision. According to the American Killifish Association, Nematolebias is the preferred (scientifically correct) generic name. For the purposes of this article, I’m going to use the older name, simply because the fish is most often available under this name, even in the AKA's Fish and Egg listings!
C. whitei hails from Brazil, in the savannah regions around Rio de Janeiro. It is a true annual fish, an inhabitant of pools that are empty or nearly so during the dry season. The adults deposit their eggs in the mud bottom of these temporary pools, where they remain dormant in the damp earth until the next rainy season. An amazing adaptation, but this is what makes this unfortunate fish a candidate for extinction. “Rio-by-the-Sea-O” is a popular resort area, and the areas where C. whitei occur look like the rest of the savannah, a gently rolling plain covered with grasses. The depressions that fill with water when the rains come are easily filled in or paved over when dry to make room for development.
Those lucky C. whitei eggs that avoid this fate will remain dormant for several months until hatching commences within hours of the eggs becoming inundated again. Not all eggs hatch-some continue to rest and will only hatch after one or more re-dryings. This serves to maintain a population in the pool even if there is an early rain or the rainy season is short and the pool dries up before the fish have a chance to spawn.
The young that hatch and survive will be sexually mature and breeding in about four weeks! Within less than a year, they will have buried hundreds of eggs, attained their full adult size of about 4", and their bodies will be drying on the caked mud, providing fertilizer for the grasses that will cover the now empty pond.
In an aquarium, drying is not an issue, and they may reach the ripe old age of 14 months or more. They are not finicky about food, eating live, frozen, and flake with gusto. As far as temperatures go, they are from a region known for its warmth, and the shallow pools they inhabit can get quite hot. There is no need to imitate these conditions exactly-the mid 70’s F. are fine for long-term care and breeding, and will extend their lifespan. Water conditions are not much of an issue: They can occur in pools near the sea, so a slight salt content is tolerated quite happily and prevents disease. Their native waters tend to be acidic and soft, but hard, alkaline water serves quite well. Try to keep the pH below 7.8, but this will be easy as the fish spawn best into peat.
The spawning tank does need to be simple in layout, and the reasons for this will become obvious when you understand how they spawn.
Like killifish are often divided into "plant spawners" and "substrate spawners", annual killifish are often divided into "plowers" and "divers". These designations refer to their preferred method of spawning. With "plowers", the pair lines up side-by-side and deposits eggs and sperm with their vents pressed against the substrate. A flick of the fins buries the fertilized egg. In "divers", the pair actually lines up side-by side and dives into the substrate, disappearing from view temporarily. C. whitei and its relations are members of this latter group, so to observe typical spawning behavior, a deep layer of substrate is needed. Peat is the ideal substance for this application. It not only allows the fish to dive, the eggs can be incubated in the substrate they were deposited in (no need to pick eggs! To be honest, there isn’t really any other substrate that annual eggs can be incubated on as effectively), it acidifies the water and adds tannins that improve the overall health of the fish. Peat diving is also messy, and for this reason you should keep the bottom of the tank bare. If you are able to obtain some C. whitei, you’ll most likely be dealing with someone who can bring you up to speed on the various sources of peat and methods of handling it. I could devote an entire column to that alone, so I’ll let your killie source give you that info.
How can you provide a deep peat layer without covering the entire tank bottom? Luckily, most Cynolebias will use a spawning box filled with peat. Small plastic food boxes or yogurt containers with holes cut in the lid and then filled with a few inches of peat will do the trick.
The number of eggs produced is fairly high, so I recommend removing the peat every week, and replacing it with fresh peat. Now comes the fun part. Pour the collected peat through a fine net, and then squeeze LIGHTLY to remove excess water. You want the peat to drip little or no water when lightly squeezed. You may let it dry on black and white newsprint for a few hours if it still seems too soggy. Once you have your moist peat ready, you’ll need to put it in a bag- pet-shop fish bags, or even food storage bags will work very well. You may want to double-bag to prevent excess drying. This is crucial because your bag of egg-filled peat is now going to incubate for three months or so. That’s not a misprint. I hope you’re not in a rush. Incubate the peat somewhere dark and fairly warm- the upper 70’s F to low 80’s F. I had terrific luck using a shelf above some plant lights. The eggs were subjected to temps in the low 80’s during the day, and dropped to the low 70’s at night. It is a good idea to label and date each bag, so that you can keep track of when the peat should be placed in water.
Okay, you’ve waited about three months and can’t take it anymore, so you want to check to see if the eggs are ready. What you need to do is find some eggs in the peat (harder than it sounds-use a magnifying glass) and look for the eyes. An egg that is fully developed gives a fairly reliable indication it is ready-the iris of the eye is clearly visible, bright, and, most important, fully formed in a complete ring around the eye. If all the eggs you find have this fully developed iris, they are ready to hatch.
Put your peat in the hatching container (a plastic shoebox, a small aquarium, whatever) and add the hatching water. The hatching water should be soft, if possible, and room temperature. Several inches of water will do the trick, and in a few hours you should see hatching begin to take place. I normally aerate the water with an airstone at this point. Within 24 hours or so, all the eggs that are going to hatch will have done so. The leftover peat can be collected, re-dried and stored for another few weeks-there are usually some eggs that take a second wetting to hatch.
The fry are easy to raise on live baby brine shrimp and sometimes are large enough to take grindal worms as a first food. Feed several times a day, if at all possible, and keep the water clean–a brigade of snails will take some of the pressure off, but without high water quality the fry will never grow to their full potential. Within a matter of two to three weeks, the fry will begin showing their adult colors and can be sexed easily, and after a month or so, they may be ready to spawn.