KILLIFISHES
The egglaying Cyprinodonts have always been regarded as difficult because they are believed to require special conditions, namely soft acid water, but while this is true for some species it certainly isn’t the rule for all of them. Many are exceptionally colourful and this alone makes them good aquarium fishes, but to see them at their best requires dedication on the part of the aquarist. It takes a lot of time and patience to maintain banks of small species aquaria, remove eggs from spawning mops, or dry out peat and then raise the fry. For those of us who have kept killifishes the work involved is worth it. If you haven’t very much space, then try with a single species tank.
In nature, killifishes are found throughout the tropics with one exception, Australia, and some have even entered the temperate zones. Most are small fishes, but a larger one that is becoming a fairly regular import is Lamprichthys tanganicanus, from Lake Tanganyika, which can grow to 13 cm (5 1/2 in). This is a really
beautiful fish, with a pale yellowish body overlaid by brilliant blue spots in the male, or silver spots in the female. This is a hardwater killifish which will fit in well with other fishes of a similar size, although it is best kept in a school of 6 to 10 individuals.
Killifishes are predominantly insectivores, and a supply of live foods is very important as some will refuse to take anything that doesn’t move. Daphnia, Cyclops, and mosquito larvae are the usual standbys, but you can also hatch brine shrimp eggs, or culture whiteworm and microworms, to feed to your fishes. Feeding is very important if you are to achieve any success in breeding them, and this applies not only to getting the adults into condition but also to growing on the fry. It is frequently a lack of attention to correct diet rather than water quality that brings about the demise of many killifishes (and so deters the amateur aquarist from continuing with these fishes). Another factor in their demise can be a poor choice of companion fishes. For example, the trailing finnage of the males is far too great a temptation for some of the barbs which will harass the killifishes, damaging their fins. This can lead to a fatal infection or to the killifishes being bullied to the point where they are prevented from feeding. Needless to say, most species are best kept in a single-species aquarium.
Substrate Spawners
Sometimes referred to as “annual fishes”, these killies inhabit ponds that evaporate during the dry season so that the adult fishes perish. To ensure the survival of the species, the fishes spawn in the substrate and the developing eggs remain in the dried-out mud until the next rains. Not all the eggs hatch at the first wetting. This is because if the first downpour turned out to be a freak shower and the pond then dried up again, the fishes would die out. Some of the eggs, therefore, need a second or even third wetting before they will hatch, thus securing the survival of the species. Aphyosemion oeseri deposits its eggs on fine-leaved plants. Alternatively use mops and pick off the eggs, ready for hatching in another tank, which should be filled with water from the breeding aquarium.
In the aquarium, some substrate spawners (“annual” fishes) can live for longer than a year because their water source does not dry out.
Examples of this method of reproduction are the South American genera Cynokbias and Pterolebias, and the African genus Nothobranchius. Each species has its individual requirements, for example water temperatures and exact storage time for the eggs, so you will need to check up on these, but we will give you some general guidelines for breeding these fishes.
Breeding Substrate Spawners
The males are larger than the females with intense coloration and extended finnage; in total contrast, the females are normally a pale grey/brown and much smaller, so it is easy to tell whether or not you have a pair. It is normal to have to buy them in pairs, but if you are trying to breed from them, it is best to have one male and two females. This is because the male will drive the females very hard when spawning, and by introducing two females into the aquarium he has to divide his attentions between them.
Prepare the breeding aquarium with a peat substrate 4-5 cm (1 1/2-2 in) deep and add a couple of clumps of fine-leaved plants such as Elodea or Myriophyllum as cover for the females. The water should be mature, soft, slightly acid (the peat will do this), and about 25 cm (10 in) deep. Sometimes it is necessary to boil the peat before put it in the aquarium so that it will sink. Boiling also sterilizes the peat, so the eggs are less likely to suffer from any bacterial or fungal infections.
Condition the parents well with plenty of live foods such as Daphnia and insect larvae. When the females are full of roe place them in the breeding tank and allow them to settle before adding the male. His courtship display to the female consists of displaying his fins and posturing. If she is ready to spawn, the pair will dive into the substrate, the male clasping the female with his fins. In some species the pair disappear beneath the surface of the substrate, but in others the fishes seem just to push the eggs down into the peat. Once spawning is complete, the female will appear very thin and rest on the bottom. Remove her to another tank to recover and feed her well. The male should be placed in another aquarium until the female is ready to mate again.
Now you can drain the water and peat from the spawning aquarium through a net. An old pair of tights is useful for this but make sure there are no holes or ladders in the bit you are using, and don’t forget to check with the owner first to make sure you can have them! Squeeze the water out of the peat so that it is damp and crumbly, then check it for eggs. Depending on the species, these will be small brown or white spheres about 1 mm G/32 in) in diameter. Assuming that you find some, you can then store the peat and eggs in a plastic bag for the recommended time for that species. This is usually 3-4 months. LABEL THE BAG WITH THE SPECIES NAME, AND DATE IT. There is nothing more annoying than taking a guess at what’s in the bag and how long it has been in the bottom of the airing cupboard. Eggs should be stored at a temperature of about 22—24°C (72-75°F); the bottom of the airing cupboard is usually ideal but make sure by leaving a maximum/minimum thermometer in there for a while, and checking it each day to see what the average is.
After the requisite period of storage the eggs can be hatched. But before you start hatching them, prepare your fry food by setting up a brine shrimp culture so that the eggs hatch to coincide with fry needing to be fed -many fry have been lost because fry foods were not ready at the right time.
Place the peat/egg mix in an aquarium and add rain water which has been warmed to about 22°C (72°F). With any luck, within 24 hours you will see fry emerging. If you don’t, then add some live food, e.g. Daphnia, to the aquarium; these will decrease the oxygen content of the water and this should trigger hatching. The fry of most species are large enough to take newly hatched brine shrimp as their first food. Don’t forget to dry the peat out again and store it for another month before re-wetting as there may still be some dormant eggs in it.
Popular species of this type of killifish include Nothobranchius guentheri, Nothobranchius rachovi, Cynolebias bdlotti, Cynolebias whitei, and Cynolebias nigripinnis.
Breeding Plant Spawners
The killifishes which lay (or, more correctly, hang) their eggs from plants are considered easier to breed. Again set up a breeding aquarium, but this time use a gravel substrate and either fineleaved plants or spawning mops. Most people use spawning mops as they are more convenient than plants and can be removed every couple of days to harvest the eggs.
Spawning mops are made of yarn attached to a cork or polystyrene float so that the yarn hangs down into the water. Alternatively, they can be attached to a stone so that the yarn floats upwards. You will need to check where the fishes spawn – up in the plants or near the substrate – so that you can position your mops accordingly. If you don’t know, provide both types.
Again, condition the parents well on live foods before placing them in the breeding tank. The male will chase the female through the plants/mops and some eggs will be deposited at each pass. Check the mops every couple of days and pick off the eggs. Some species lay them close to the knot at the densest part of the mop, others lower down the strands. Place the eggs in shallow containers (small ice cream containers or margarine tubs are ideal) with water from the breeding tank to hatch. The containers can be kept on top of the aquarium or floated in it – either way they should not get too hot or too cold. On hatching, feed the fry on newly hatched brine shrimp, but be sure to keep the fish-hatching containers clean and free from debris by regular, small, partial water changes. Once large enough the fry can be moved to an aquarium to grow on. This method of reproduction is practised by many members of the genus Aphyosemion and these highly coloured fishes are much prized amongst hobbyists. Popular species which are sometimes found in retail outlets include Aphyosemion australe, Aphyosemion gardneri, and Aphyosemion striatum. Other recommended species include Epiplatys dageti, Epiplatys sexfasciatus, and Rivulus cylindraceus. All require soft slightly acid water for breeding. Hard water species which breed in the same way include Cyprinodon macularius, Cubanichihys pengellei, Fundulus chrysotus, and Profundulus labialis.
Other Spawning Methods
As with all groups of fishes there are exceptions to the rule. This is certainly true of killifish reproduction, and there are many species which do not fit into the two neat groups described above. Xenopoecilus species, for example, use internal fertilization of the eggs which are then expelled by the female and hang from her vent like a bunch of grapes. They remain attached for the full 15 to 20 days it takes the embryos to develop before they hatch. Fishes that reproduce in this way are sometimes known as “egglaying livebearers”.
Another species which bucks the trend is Jordanella floridae (American Flagfish). In this species the pair lay their eggs at the base of a clump of plants or in a fanned-out depression in the substrate (sand is the best substrate for this). Spawning continues for several days after which the female should be removed. The male continues to look after the eggs and young until they are large enough to fend for themselves.