The Annual Killifish of South America

Author: Charles Nunziata

Annual killifish from South America not only sport amazing looks, they have fascinating life cycles. One killifish enthusiast profiles the different species and offers breeding advice on these wonderful fish.

Annual Killifish Basics

Annual killifish are found in both Africa and South America. South American species are found throughout the continent, from Venezuela to Argentina, while only one genus, Nothobranchius, is found primarily in the eastern regions of Africa. The South American group includes an enormous array of genera and species that vary in size, colors, patterns, and finnage. There are species with bodies under 2 inches to relative giants at 6 inches or more. Bodies vary from short and deep to large and elongated, incorporating delicate pastels overlaid with iridescence, patterned in spangles and stripes.

There are plain, rounded fins with spots, stripes, and borders, and those that elaborately flow in multitudes of colors and patterns. Together with their extraordinary breeding and survival strategies, the 28 or so genera and hundreds of species, subspecies, and recognized populations make South American annual killifish one of the most interesting and underappreciated groups of fishes available in the hobby today.

The term “annual killifish” refers to killifish that live their entire life in temporary bodies of water, those that fill when the local wet season commences and completely desiccate during the ensuing dry season. To thrive and propagate in perhaps the most demanding and dynamic environment faced by any aquatic vertebrate, these marvelous fishes have developed an extraordinary and complex web of inter-related and mutually supportive survival adaptations. These include extremely rapid growth, very early sexual maturation, and great fecundity.

Annual Killie Lifecycle

The process from hatching to reproduction is continuous but is best described as a series of discrete events. To simplify, let us start with a pool full of killifish, vibrant and spawning. Annual killifish deposit their eggs in the substrate, burying them to various depths. As the dry season proceeds, the water slowly and continuously evaporates and all remaining fish perish as the water disappears. The eggs, below surface, are isolated from the atmosphere and remain so as further drying solidly bakes the substrate.

As the dry season deepens, however, the surface becomes so dry that it fractures, resulting in deep cracks in the baked surface, exposing the eggs to atmospheric gasses and greater fluctuations in temperature. When the rains again fill the pool, anaerobic conditions around the eggs trigger hatching.

Egg Development

The deposited eggs proceed through a sophisticated series of developmental events that begin immediately after spawning and continue at various rates through the remaining life of the pool and the subsequent dry period. Depending on very complex environmental interactions, annual eggs do not develop at uniform rates, but rather respond with periods of development, interspersed by one or more periods of suspended development called diapause. All these occur in response to a combination of environmental cues. These environmental cues trigger both the onset of the diapause events as well as the resumption of the incubation process between them. In addition, individual eggs do not respond uniformly. Some remain at one of the diapause stages while the others resume development. After one full cycle, the substrate will typically hold eggs at virtually every stage of development.

This episodic developmental process is part of an astonishing adaptation to the unreliable timing of the onset of wet seasons and acts as a fail-safe defense against the occurrence of long-term droughts. What appears to be random variation in the developmental cycle is, in reality, a sophisticated survival mechanism that guarantees that some eggs will always be ready to hatch despite extended droughts, erratic short-term rain events, or extended periods of flood.

Returning Rains

Whenever the rains do return, inundation initiates a complex and radical change in the environment around the eggs. That triggers completely developed eggs to hatch within hours and those near final development to complete the process within days. Depending on the species, the resulting fry will reach sexual maturity and breed in a few weeks to a few months. They will bury their eggs in the substrate from which they recently emerged, seeding the future generation.

At times, annual rains are intermittent. Pools fill for very short periods and then dry again, perhaps until the following cycle. Under these circumstances, natural selection tends to favor the fish that most rapidly mature and breed, passing these characteristics to the next generation. All life processes are accelerated, including the aging cycle, which is more or less synchronized with the wet cycle of the pool.

The term “annual” comes from this natural annual cycle as well as observations of lifespan in captivity. Wild caught annual killifish often expire within a year of age, but after decades of domestic husbandry, many species will live to 1½ years or more. A full understanding of annualism in killifish is still a subject of intense scientific study, and a complete unraveling of this fascinating process is, no doubt, some decades off.

Breeding South American Annuals

However, if one can tolerate the uncertainty, breeding South American annual killifish presents a unique challenge that many find seductive. In essence, the breeder must employ a material that substitutes for the pool substrate and a storage regimen for the developing eggs that substitutes for the wet-dry season. Each adds a dimension to fish husbandry not otherwise found. Fortunately, e easy and effective solutions have been developed by killifish hobbyists over the last 50 years.


Isolating the breeders and preconditioning them with live or high-quality frozen foods for a week prior to spawning will greatly increase the chances for success. Although breeding can be accomplished in a permanent aquarium, a special breeding setup often provides better results. Colloquially known as divers, South American annuals completely submerge in the muddy bottom of the pool substrate to breed. The material of choice to simulate this substrate is a good grade of fertilizer-free peat moss or fiber. To prepare the material, boil it for a few minutes to kill any unwanted organisms and to ensure that it will sink.

Spawning Targets

To trigger the spawning response, a spawning target that mimics the pool substrate is required. If breeding is to be done in a permanently set up tank, select a plastic container with a depth of at least three times the length of the largest fish to be bred and cut a hole in the container cover that is two to three times the breeder’s width. This hole allows the fish to enter and leave while minimizing the entry of food or other contaminants. It also minimizes the amount of peat that the fish will throw up and out of the container during spawning.

Add gravel or other weighty material to the container to ensure it will sink in the tank. Fill the container halfway with water from the breeding tank, and add some prepared peat. Skim off the peat that does not sink, and add more water and peat until the container is completely filled and the peat layer is at least 50 percent deeper than the length of the largest breeding fish. Pop on the cover and slowly immerse the container into the tank so as not to disturb the peat. The annuals will eventually find the container, enter it, and spawn. Remove the container after one week.

An easier, and ultimately more productive, method is to use a drum bowl or other container as a temporary spawning site. Fill the bowl with water from the breeder’s tank, and add peat as above until the desired depth is reached. For most species, a 2-gallon drum bowl is adequate. After the peat settles, add the breeders and cover the tank or bowl. The female will generally release her full complement of eggs within 8 hours, 24 at most. If the species is large, add an air stone. Do not feed during this time. Remove the breeders within 24 hours, or earlier if the female is being abused.


Up to this point, we have simulated the pool substrate, and hopefully, the fish have deposited their eggs deep within it. Pour out the contents of the container through a fine net, capturing the peat. While the peat is in the net, squeeze out as much water as possible. Then place the mass of peat moss between several sheets of newspaper, roll it up, and allow the bundle to dry at room conditions. Examine the peat after 24 hours; it should have a trace of dampness but not be wet. Pinch a small quantity between your fingers—if no water emerges, the peat is dry enough. If still too wet, repeat the process.

When ready, pack the peat in a plastic bag, mark the date of packing, and add the recommended incubation time for the species. Some hobbyists store in a temperature-controlled incubator, but most store the eggs at room temperature. The eggs will now go through their complex incubation process without any additional input from the aquarist. Incubation times vary for each species, from three to seven months or more, and are especially dependent on the temperature at which the eggs are stored. And although advanced hobbyists do manipulate incubation times, it is not recommended for those without extensive experience.


There are two methods to determine whether the eggs are ready to hatch: test hatch or direct examination. Highly experienced hobbyists are able to find developed eggs among the particles of peat and visually determine whether they are fully embryonated. However, the skill is an acquired one that many killifish hobbyists never really master. Most hobbyists test hatch: Shake the peat in the bag, remove a small quantity, and place it in a one-gallon tank or clear container.

If the eggs are ready, they will hatch within 24 hours, sometimes much sooner. If no eggs hatch, reseal the bag, store for another four weeks, and then repeat the test. When the test is positive, prepare a 1- or 2-gallon tank with active tank water, dump in the peat, and stir to wet it as much as possible. Most of the peat will sink in a few hours. When successful, the event is what killifish hobbyists refer to as the hatch. There is nothing quite like it—it is an event one has to experience to truly understand.

Raising the Fry

Newly hatched fry of most South American annual species are small and difficult to see. A bright light source applied around the tank and a finger tap on the side will cause the fry to move, making detection much easier. With practice, it becomes quite easy to detect even the smallest fry this way.


The larger fry can feed on newly hatched brine shrimp, but the fry of smaller species require proportionally smaller foods during their first week of life. All killifish fry, regardless of size, consume microscopic foods immediately—paramecia, infusoria, etc. If the hobbyist does not raise microscopic foods, a clump of seasoned java moss, Riccia, or hair algae can be added. The latter in particular fosters enormous colonies of microscopic life. Newly hatched brine shrimp can be taken within days and should be offered through the first several weeks.

After a few weeks, microworms, then whiteworms, grindal worms, or finely ground prepared foods can be added.


Growth is very rapid and all manner of foods can be taken at a month. Water cleanliness is essential to prevent disease among the fry. Daily water changes should be made the first week, followed by several changes each week thereafter until the fry are well established. If possible, live plants should be kept with the fry during these first critical weeks. Within a month or so, there will be annual killifish ready to breed, closing one cycle and opening a new one.

A Diverse Group

Within the last 20 years, the group of South American annuals has expanded from a handful of genera to the number we now have. The opening of the rainforest throughout South America has led to the discovery of many new species and unique populations. It is likely that many new species and additional genera will arise as exploration proceeds. Note that many internet sources are not up to date and identification errors are common, adding to hobbyist confusion.

Regrettably, the vast number of new species cannot currently be accommodated by the hobby, and many species are found, described, and passed through the hands of hobbyists without being fully established. More importantly, the frantic pace of development and discovery makes it difficult to determine the status of these new species in the wild, seriously compromising conservation assessments.

Within each genus, one will find similarity in fin structure and body type but not necessarily in size or coloration. A few genera include both large and small species, while some are populated primarily with large species that exceed 4 inches and others with quite small ones rarely exceeding 2½ inches. The larger species are far less common in the hobby. They tend to have long incubation periods and, with some exceptions, are not overly colorful. Spawning and grow-out facilities put a demand on the smaller fishrooms killifish hobbyists tend to have, limiting the number of hobbyists able to successfully handle the giants among the group.


The commonly available members of the genus Aphyolebias, A. peruensis and A. wischmanni, grow to 4 and 5 inches respectively. They are characterized by long, slender bodies and elaborate caudal fins. The lesser-known members of this genus are rarely seen in the hobby.


All Austrofundulus species have deep, robust bodies and, with a few exceptions, rounded fins. Many in the group have a noticeable contrasting crescent marking in the caudal. A. transilis, with its many populations, is periodically available in the hobby.


Austrolebias is a genus with more than 40 species, most of which are heavy-bodied and stocky. The unpaired fins are rounded. The giants of the genus include A. elongatus, monstrosus, and prognathus, all brutes that exceed 6 inches, with large mouths and the disposition to match. Most members of this genus, however, are less than half that size, and several feature contrasting bands or pearly spots on brown, blue, or green bodies and fins. The iconic A. nigripinnis presents an absolutely unforgettable sight when spawning; body and fins turn velvet black suffused with numerous pearly white spots.


Recent nomenclatural studies have reclassified many of the most common annuals from Cynolebias to other genera, leaving just 14 species that are rarely seen in the hobby. The remaining members look very much like smaller versions of the genus Austrofundulus.


A physically small but exceedingly beautiful group of killies, Leptolebias spp. are less than 2 inches in length. They feature moderately slender bodies that are elaborately marked and intensely colored. L. splendens and aureoguttatus in particular are absolute jewels with dramatic red markings on the body and fins. Unfortunately, Leptolebias species are not commonly available.


All Moema species are very large, some exceeding 7 inches. Their bodies are marked with dots, and some exhibit dark scales that suggest parallel rows along the midsection from the operculum to the caudal peduncle. These are large, impressive fish that are best kept by specialists.


A group of very-small-bodied killifish, the largest Plesiolebias spp. are under 3 inches in length, and the smallestare barely visible at 0.7 inches but brilliantly colored. Only the unnamed Plesiolebias sp. Xingu is periodically available.

Simpsonichthys, Hypsolebias, and Spectrolebias

There is great activity in the scientific community regarding which of a group of more than 50 species belong to the genera Simpsonichthys, Hypsolebias, or Spectrolebias. Most species remain in the genus Simpsonichthys, but this may change in the future.

This group contains some of the most beautiful killifish of all. All are well colored, most with wonderful combinations of brilliant and subtle colors and patterns. All are small at less than 3 inches in length, and most are less than 2½ inches. Unpaired fins are rounded in many species, but some have extended dorsal and anal fins as well as ray extensions.

One group of particularly beautiful species exhibits blue dots arranged into stripes and bars in the unpaired fins, and orange bodies overlaid with iridescent scales, sometimes forming delicate bars (Simpsonichthys carlettoi, S. magnificus). Others show dramatic bars on warm-brown bodies (S. sp. urucuia, S. ocellatus, and Hypsolebias guanambi).

Many species have elaborate fins suffused with spots, and brilliantly bordered anal fins, some with contrasting colors along the fin rays (S. marginatus, S. reticulatus, and S. fulminantis). One has a scarlet body overlaid with brilliant blue spots (S. picturatus), and others have densely packed bars of red and brown (S. parallelus). Many of these species have become available only in the last several years and represent a kind of golden age for South American annual fishes.

Additional Genera

Lastly, there are approximately 18 additional genera that are monotypic or contain six or fewer species. They include Compellolebias, Cynopoecilus, Gnatholebias, Llanolebias, Maratecoara, Micromoema, Nematolebias, Neofundulus, Notholebias, Ophthalmolebias, Papiliolebias, Pituna, Pterolebias, Rackovia, Renova, Stenolebias, Terranatos, and Trigonectes.

Although some of the most interesting South American annuals belong to these genera, most are not commonly available. Perhaps the most intriguing is Terranatos dolichopterus, with its spectacularly long unpaired fins. The body is less than 2 inches in length, but the distance between the dorsal and anal fin tips is often greater, making it perhaps the most exotic looking of all killifish. A picture of grace and elegance is the equally spectacular 4-inch Gnatholebias zonatus. It sports long caudal-fin-ray extensions, a broad and sweeping anal fin with extended posterior rays, and extraordinarily long ventral fins.

There is the 2 inch Maratecoara lacortei, a long-finned jewel, and the under-2-inch Notholebias minimus, a heart stopper suffused with red on a blue body, and red stripes on yellow unpaired fins. Cynopoecilus melanotaenia features a slim body with an unusual concentration of two or three lateral rows that extend from the operculum to the caudal peduncle. And with its long, graceful, 4-inch body, Pterolebias longipinnis exhibits elaborate dorsal-fin-ray extensions. It is also one of the easier South American annuals to breed and maintain and remains a popular and available species.

Ready for Killies?

There you have it, a very brief orientation of the South American annual killifish. They provide an extraordinary opportunity to not only experience some of the most beautiful fishes in the hobby, but also to participate in one of the most unique survival strategies employed by any vertebrate on the planet. Participating in life at this level has a special quality I think, one that motivates so many of us that have spent the better part of our adult life keeping and breeding killifish. Try a killie or two; you won’t be disappointed.