The genus Nothobranchius includes more than 40 described species which occur in the sub-tropical and tropical parts of east and southeast Africa that are subject to seasonal rainfall. One species, Nothobranchius rubroreticulatus, is also known from the Lake Chad region of west Africa (and from southern Sudan), representing a relic of past times when the drainage systems in that part of Africa were linked to those of east Africa. Within the genus Nothobranchius, five subgenera are recognized: Nothobranchius (sensu stricto); Adiniops (similar to Adinia, genus in Fundulinae);Zononothobranchius (=bandedNothobranchius); Aphyobranchius (=combination ofAphyosemion and Nothobranchius); and Paranothobranchius(=above Nothobranchius, ancestor of Nothobranchius). In addition to the described species, there are numerous as yet undescribed species and many populations of uncertain affiliation. As a reference to those Nothobranchius species and populations that are, or have been, in the killifish hobby at some time or another, the reader is referred to the clickable map showing distributions, on this site.That compilation is also very useful as a source for the correct and complete names and collection codes for many Nothobranchius species and populations presently in the hobby.
Distribution and Habitat
Nothobranchius species are known from: northeastern South Africa, Caprivi Strip (Namibia), Zambia, southeastern Congo (DRC), southeastern Zimbabwe, Malawi, Mozambique, Tanzania, Kenya, Uganda, Somalia, southwestern Ethiopia, southern Sudan and in the vicinity of Lake Chad in Chad and northern Cameroon.
Typically, Nothobranchius habitats are situated on flat-lying floodplain areas and all have one thing in common – they dry completely or, in some cases, partially, on an annual or semi-annual basis, depending on the rainfall characteristics of the particular region. In detail, the habitats may be quite varied and some even owe their presence to the activities of humans. The most common natural habitats are temporary isolated pools and flooded grassy areas or marshes, which are very often closely associated with, and adjacent to, permanent stream systems. Certain human activities can also result in temporary bodies of water in which populations of Nothobranchius can become established. These take the form of rice fields, drainage ditches associated with agricultural and road-building activities, and pools that form at culverts under roads.
Nothobranchius habitats invariably have a substrate of fine sticky black mud into which the fish will deposit their eggs. At the end of the rainy season the water in the pool will fairly quickly disappear, as a result of a lowering of the water table and evaporation, and the eggs will remain in the almost dry mud for the duration of the dry season. The eggs are perfectly adapted to such conditions and will develop in stages, interrupted by periods of dormancy (diapauses or resting phases). The length of time the egg remains in any particular resting phase will depend on a variety of factors but most of the eggs will be ready to hatch soon after the onset of the following rainy season. A small proportion of the eggs may become locked into an early resting phase, resulting in prolonged development, perhaps even through a second dry season. This is nature’s way of ensuring the survival of the species should the rains fail one year or should the pools dry up before the young fish reach maturity and are able to spawn. In most parts of east and southeast Africa there is one main rainy season and a fairly long dry season per year; in other areas, such as around Lake Victoria, there are two distinct rainy seasons separated by two dry seasons every year. Furthermore, the duration of the wet and dry seasons can vary enormously across the range of distribution of Nothobranchius fishes. Consequently, the length of time that the eggs have to remain in a dry state (the incubation period) will vary depending on what part of the region the particular species inhabits.
With the onset of the rainy season, the mud in theNothobranchius habitats is moistened, the eggs therein are triggered into the final stage of development (by the change in environmental conditions) so that when the rains come in earnest and the pools fill up with water, the eggs hatch and a new generation begins. The fry grow extremely rapidly and may be sufficiently mature to spawn within 3 weeks of hatching. Rapid growth is essential because of the ephemeral nature of their existence – they have to reach maturity and spawn before the habitat dries out again, in order to ensure the continuance of the species. In view of this highly specialized life cycle,Nothobranchius are regarded, in general terms, as “annual” killifishes.
Maintenance and Breeding
In our fish-rooms, we propagate Nothobranchius species by simulating the annual life-cycle. The adult fish are provided with a spawning medium in which to deposit their eggs. This is most commonly boiled and rinsed peat moss, although the fish will also spawn in other media; for example, sand. The peat moss can be placed on the bottom of the tank to a depth of about half an inch or, alternatively, can be placed in a plastic container in the tank with a 2 inch hole cut in the lid to provide access for the fish. The fish will soon find their way into the container to spawn in the peat. The latter method has the advantage of minimizing the amount of peat moss needed, especially important when a large tank is used, is easy to harvest and keeps pollution of the peat to a minimum. After allowing the fish to spawn for a period of 1-3 weeks, the peat (hopefully including eggs) can be placed in a fine-mesh net, squeezed to remove excess water, and allowed to air dry further until it reaches a suitably moist (but not soggy wet) state. It can then be sealed in a plastic bag, labeled appropriately with species name, population, collecting code (if available), date of collection of peat, spawn period, and any other information that is deemed useful (e.g. estimate of hatching date). The bag containing the spawning can then be stored at about 75 oF for the required incubation time. The incubation time will vary depending the particular species involved and many other factors. As a guide, a table of recommended incubation times for some species commonly maintained by hobbyists, is included below.
After the necessary incubation time, inspect the peat. If the spawning contained a reasonable number of eggs, these should be visible and if ready to hatch, the eyes of the fry should be clearly visible in the egg. The peat should then be immersed in fresh but mature water, with a depth of about 3 inches, taking care to break up all the lumps and ensure that it is thoroughly wetted. Much of the peat will float and this can be gently skimmed off and discarded or reused. The eggs will sink quite rapidly when they become wet so, if the peat has been thoroughly wetted a stirred up, no eggs should remain caught up in the floating peat. If the eggs are fully developed, hatching should begin within a couple of hours. It may be some hours before the fry are able to swim normally so do not be alarmed if they appear initially to be “belly-sliders”. However, there will, invariably, be a certain number that will remain as “belly-sliders” and these are fry that have either been allowed to develop for too long or, as is more often the case, those that have hatched too early.
Most Nothobranchius fry are large enough to be able to consume newly-hatched Artemia nauplii soon after hatching. A few species (such as Nothobranchius rachovii andNothobranchius eggersi) may require infusoria for the first day or so but this is not always necessary and depends to some extent on the robustness and vigor of the particular batch of fry. Fry of all the Aphyobranchius subspecies are extremely small and will certainly require infusoria for at least a week or two before being able to consume Artemia nauplii. Aphyobranchiusfry are generally difficult to raise and, consequently, members of this subgenus are not recommended for the beginning hobbyist.
As soon as the newly-hatched fry are eating well, they should be removed from the hatching container and transferred to another similar container or to a small tank and the peat redried and stored for a further 4 weeks before wetting again. Often this second wetting will yield further fry, from eggs that have developed more slowly. As the fry grow, they should be provided with adequate space and the depth of the water increased gradually from the initial 3 inches or so to full tank height. Gentle filtration (by sponge filter, for example) should be provided. Regular partial changes of water are recommended and, as the young begin to sex out, it is advisable to separate the sexes (if tank space permits) in order to allow the females a chance to develop adequately.
Most Nothobranchius species are best to kept in water that is both alkaline and has a moderate to high hardness. The majority of natural Nothobranchius habitats have water that is alkaline and, while in many the water is not particularly hard, it is difficult to maintain alkaline conditions in an aquarium when using soft water. The use of hard water in the aquarium will also help stave off the disease Velvet (Oodinium limneticum) to which Nothobranchius species are particularly prone. For this reason, it is also advisable to add about half a teaspoonful of non-iodized pickling salt to each gallon of aquarium water. For hatching and raising the fry for the first two weeks or so, relatively soft water can be used but regular partial water changes should be carried out to prevent it from becoming acidic. Nothobranchius can tolerate a fairly wide range of temperatures but will do best at about 74-75 oF.
Male Nothobranchius tend to be aggressive, both towards each other and towards the females. The latter will be driven by the male almost constantly to spawn. Consequently, it is best to breed them either with a single male to several females or in larger groups comprising a number of males and females. Generally, if a batch of young male Nothobranchius are raised to adulthood together they will be more compatible than if they had been separated at some point. However, it is always a good idea to examine the females regularly and if they show signs of the males’ rough attention (torn fins, scales missing, hollow belly, etc.) they should be isolated until they have recovered.
A small breeding group of a single male and one or more females can be accommodated in a 3.5-5 gallon tank. Larger breeding groups require larger accommodations such as a 10 or 15 gallon tank. The size of tank required for raising the fry will depend on the number of fish; however, do not crowd them. Unless very large batches are being raised, 10 and 15 gallon tanks are generally suitable for this purpose.
Adult Nothobranchius prefer live foods (mosquito larvae, brine shrimp, white worms, daphnia, etc.) but can also be maintained on a diet of frozen foods (brine shrimp, blood worms, beef heart, etc.). Chopped earthworms also constitute an excellent food. Provide as varied a diet as possible. Fry can be fed newly-hatched Artemia nauplii, microworms and vinegar eels or, in the case of the very small fry, infusoria. As the fry grow, their diet can be supplemented with the same fare as provided for the adults, but finely chopped or mashed.
Anyone setting out to keep Nothobranchius species should be aware of the susceptibility of members of this genus to the disease Velvet. The first signs of this disease are clamped fins, sometimes accompanied or followed by an accelerated rate of respiration. The next stage will be the appearance of a dusting of fine yellow spots on the fins and body. There are numerous commercial remedies available that are quite effective but prevention is far better than cure because often the fish will be left in a weakened condition and, in the case of fry that become infected, it is invariably fatal. This disease will be rare if one observes a few simple basic rules: keep the water clean, carry out regular partial changes of water, do not overfeed, siphon out any uneaten food immediately if overfeeding does occur, and do not overcrowd the tank.
Recommended Incubation Periods
Below is an abbreviated listing of recommended incubation times for certain selected Nothobranchius species that are commonly maintained by hobbyists. Note that where there are numerous populations of the same species in the hobby (e.g.Nothobranchius eggersi, Nothobranchius kafuensis, etc.) the data have been generalized. The following should be used as a very rough guide only, as incubation times can vary widely depending on specific conditions.