Killifish are a group of small egg laying fish with a worldwide distribution. They occur on all the continents except Australia and Antarctica. They can be found in full marine water to water 5 times saltier than sea water of water as soft as distilled. They live in esturaries, streams and small rivers, lakes and swamps and even in floodplains that only run seasonally. This has lead to a unique way of survival in some genera of killifish. They survive harsh conditions by the killifish egg being able to remain dormant months after the water has evaporated and their parents have expired. These killifish are sometimes referred to as annual fish. Their mode of reproduction is both fascinating and with N. guentheri, fairly easy.
The genus Nothobranchius includes a number of species that for the most part are found in east Africa. Nothobranchius guentheri comes from a small area along the coast of Tanzania. It lives in a series of small temporary pools that dry out for short periods during the African summer. There are usually two rainy seasons in this region, a long rainy season during the winter months and a shorter one during the summer. Many of the Nothobranchius found in this region have a relatively short incubation period as the dry seasons are short in duration. N. guentheri is one of the species with a short incubation time.
A brief life history of N. guentheri
After spending several weeks developing in the egg, the larval N. guentheri is ready to hatch. Due to a unique development in it’s egg, they are able to go into a resting state where it’s metabolism nearly shuts down. This is called diapause and it is marked by several stages. Diapause stage one is where the egg suspends all developement. This is a survival strategy that occurs if the rainy season is early and the pools dry back out. Diapause stage two is where they embryo developes and about mid way through it’s development it goes into diapause. Stage three is where the egg fully developes and will hatch upon the return of the rains. A reduction in oxygen as the eggs are submerged seems to be the trigger for hatching. All stage three eggs will hatch. The first and second stages will continue their respective development to stage two and three. This insures that if the rains return too soon and the pools dry our prematurly that there will still be eggs to hatch. Hatching alongside the little killifish will be plankton of all kinds including insects, protozoans, crustaceans and other small organisms that were resting along side the killifish eggs. These small creatures feed the ravenous appetites of these killies.
Fire killies grow fast. The pools they live in can be short lived and hold water for only a few months. Therefore growth and maturity is rapid. Guenther’s fire killie can start sexing at six weeks with the reticulation on the scales appearing. Females fins will remain clear while the males fins will stat to darken. The black bar the edges the caudal fin of the males is also one of the first marks to show. As the males grow and mature the scales reflect blue and have a maroon outline. The caudal becomes deep crimson to maroon in color with a black edge. The dorsal and anal fins are large. They are yellow with dark markings. The reticulation forms a pattern of bars on the males sides. Females are plain with a grey to brown back and sides. Some scales will reflect blue. Fins are smaller than the males and they are colorless.
- guentheri begins spawning at an early age. Eggs are deposited in the substrate where they enter the various diapause stages. The adults continue spawning until the pools they inhabit become too stagnant and dry out. They eggs then repeat the diapuse stages as the pools await the next monsoon rains. This life cycle can be repeated in the aquarium with these interesting and colorful fish.
- guentheri is a small killifish growing to about 5cm long. Females are smaller. Due to their small size a pair can be housed in aquaria as small as 5 gallon. They are not too sensitive to water conditions and can live in water with a little hardness and on the alkaline side. In nature they start out in soft water, but as the mineral salts dissolve and the water evaporates it starts to get harder and more alkaline. I keep N. guentheri in a medium hard water with a nuetral pH. Slightly soft acid water also works well. I keep them at room temperature. One things I have always appreciated about killifish is their tolerance for cooler water temperatures. When kept at cooler temperatures their lifespan can be extended beyond a year.
Tank setup is simple. I will use a five gallon aquarium as an example. For a filter I like to use a sponge filter, or with a pair ot trio in this size aquarium, no filtration. I kept the bottom bare to aid in water chages. I use a goldfish bowl or glass jar to house the spawning medium in. In the case of annual killifish, the best substitute for the natural pond sediments is peat moss. I use boiled sphagnum peat moss as the medium. I place a few centimeters in the bowl and after the peat settles gently place it in the aqaurium. The fish will find it and use it. I also add some floating plants for the female(s) to hide in. Males can be aggressive drivers when it comes to spawning and be hard on the females. Males are also aggresive towards each other and will fight, sometimes with disastrous results to the underdog.
Feeding fire killies is easy. They accept a wide variety of live and frozen foods. I feed mine mosquito larvae, bllodworms and other tidbits such as daphnia and fairy shrimp. I feed frozen brine shrimp, blood worms as well as tubifex worms. A varied diet promotes color, growth, and egg production. When well fed, N. guentheri can produce large hatches. With feedings comes water changes. I recommend 25 % water changes a couple of times a week for quality maintenance of N. guentheri.
Handling of the eggs is easy. Let the fish spawn for one to two weeks before changing the peat in the bowl. I pour the peat from the bowl into a fine mess fish net. N. guentheri eggs are small, but easy to see. Usually N. guentheri is prolific enough that eggs will be visible as little clear yellow spheres. I let the peat set in the open air for a couple of hours, and while it is still moist, but not dripping, I place it into a plastic fish bag. I seal the bag and label the species, date collected and first potential hatching date. For N. guentheri it is eight weeks. Next weting after that is at 12 weeks. I usually had for weeks after each weting. Sometimes fry will hatch even after several wettings.
Raising the fry of N. guentheri is fairly easy. Hatching is an interesting affair. I take the bag of peat and pour the contents into a shallow dish, such as a casarole dish. Glass dishes are great for hatching annual killifish eggs. Some aquarist use plastic shoe boxes for killies. I have used them as well. I then cover the peat with about an inch of water, no more, and let the peat settle. After a half hour or so you will see the fry as they hatch. Fry, although small, can feed on newly hatched brine shrimp. micro worms and rotifers. Feed well for best growth. After a couple of weeks fry should be moved to larger containers so they can grow. Depending on the hatch I usuallly move the fry to a ten gallon size, then split them up into smaller numbers as they grow. Some hatches can be over one hundred fry, so plan accordingly when wanting to keep these fish. I separate the larger fish from the rest. They will eat their smaller siblings. Also the smaller fry tend to be the females. As soon as they sex out, choose the ones you want to keep and repeat.
In conclusion, N. guentheri is a very beautiful fish and it’s color and mode of reproduction will garuantee their continued success as an aquarium fish. Not only is someone introduced into the keeping of fish, but culturing live foods, collecting live foods, and exploring such things as climate and other animals that live with these unique fish can be sparked. I first kept and bred N. guentheri nearly forty five years ago. It is still one of my favorite killifish. I hope you will enjoy raising them as I have.