Annual Killifish
The rainy season comes on with a series of downpours on the parched land, and in the ponds and ditches that were dried out all during the dry season, water gradually appears and becomes deeper. Tiny fish appear as if by magic, and the water soon teems with them. They grow at an unbelievable rate and in a few months become sexually mature and mate, burying their eggs in the bottom silt. The males find territories for themselves and battle fiercely for them when another male appears, showing their most brilliant colors.
But this happy state of affairs does not last very long. The rains soon end, and the hot sun makes itself felt on the water. The result, of course, is much less water, and the fish become more and more crowded. Predators appear on the scene, as they always do when there is an easy meal at hand: kingfishers, cranes, egrets, snakes, turtles, and many others. As time goes on only the deeper spots, or what were the deeper spots, still hold water, and soon these dry out as well. The fish? They die by the millions when there is not enough water to support them. What were lovely, lush ponds become foul, malodorous puddles.
Mercifully, decay is rapid in the tropics and these areas soon become dried-out holes that bear little resemblance to what they once were. No water, but the fish life is there, just the same, in the form of eggs left by the breeding fish during the rainy season. They buried their eggs in the bottom silt, you will recall. These eggs, protected from the direct rays of the sun by this covering of silt, undergo a partial drying at this time.
Then the inevitable change of seasons takes place once more and the rain again begins falling. Life awakens within these eggs, which hatch in short order and start their strange, short life cycle all over again.
In Africa, these "annual" fishes are represented by the Nothobranchius species in the east and some of the Aphyosemion species in the west. Aphyosemion has two entirely different ways of spawning. Most species simply hang their eggs on plant leaves, where they hatch in two weeks, but the ones we treat here are the bottom-spawning species, such as Aphyosemion sjoestedti, A. occidentale, and A. arnoldi. These two genera include some of the loveliest of all aquarium fishes and are very high in cost, taking into consideration the short life span, which rarely exceeds eight months. In South America there are the Cynolebias and Pterolebias species that have exactly similar life spans.
To the fish breeder, propagating these species presents the problem of giving them similar conditions in the aquarium. Most of these species when mature and well conditioned are ready to spawn any time a male can swim up to a female. So eager are the males to spawn that many breeders make it a point to use two or three females to every male. A 2-gallon aquarium is ample in most cases. The bottom is covered with peat moss which has been well boiled in advance. Here they find a substitute for the soft mud of their habitat and lose little time digging in close beside each other and depositing eggs. Water temperature should be about 78° F., and the tank should be kept covered to keep the fish from jumping out. Live daphnia and tubifex worms are the desirable foods for conditioning, with an occasional feeding of whiteworms. Once the female has become depleted of eggs, which is shown by her lessened girth, she and the male should be taken out and kept separate until they recuperate in a week or so. This leaves a tank with a good supply of eggs buried in the peat moss. The water is then emptied carefully until there is only the wet peat moss left, and at this time the drying process is duplicated by allowing the peat moss to become partially dry and then covering the tank. The moss may also be removed to a plastic bag.
At this time a little patience is called for: the eggs must remain as they are for six weeks. Then a few inches of water is poured back into the tank. In a short time, sometimes a very short time, the fry will be seen swimming about. Sometimes the eggs are not yet fully developed, in which case they will not hatch. Leaving them dried out for another week may do the trick, and the process may have to be repeated a few times; sometimes a few hatch before the others. Various species differ in hatching times.
Granted the eggs have hatched, you will note that the yolk sacs have been absorbed and the fry swim freely. They are large enough at this time to eat newly hatched brine shrimp, and feedings should be frequent, as they consume unbelievable amounts. Growth is very rapid, as may be expected when their original home conditions are considered.
All this seems to be a lot of trouble to go to for alish that will live for only about a year or so, but this group of killifishes is among the most beautiful of all aquarium fishes. You may not have them for a long time, but they are certainly a thing of beauty while they last!
