How to Keep and Breed Chromaphyosemion Killifish

When I first joined the BKA in 1978 there was a very limited number of ‘Bivs’ available (which is another name commonly used for the Chromaphyosemion subgenus). It was a long time ago, but I remember the names Biv ‘Hollyi’, ‘Lagos’, ‘Ijebu-Ode’, ‘Funge’, and ‘Multicolour’. These fish had predominantly orange-brick red fins with the exception of ‘Funge’ which, although still had some orange, had far more blue pigmentation present than the others.

Progressively throughout the last two decades, there have been numerous trips to collect more Chromaphyosemion spp. and we now have a plethora to choose from. There are fishes that are predominantly green, a couple that show a lot of yellow and even a few that have a slate blue colour. There will no doubt be a species that will suit your personal preference.

Chromaphyosemion is a well-defined subgroup of the much larger genus Aphyosemion, but scientists are reluctant to fully separate these fish until a larger overall revision is carried out. Chromaphyosemion spp. are found across coastal regions of West Africa from Benin to Gabon, with the majority of species occurring between the Cross River (which forms the southern border between Nigeria and Cameroon) and the Ntem River (also called the Campo River) between Cameroon and Equatorial Guinea.

Chromaphyosemion poliaki "Meanja" COS 2015/01 by William King

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What is a 'Biv'?

The Chromaphyosemion subgenus includes everything that was previously known as the 'bivittatum group'. Because of this, the common name ‘Biv’ is frequently also used for these fish. This is an abbreviation of the species name bivittatum, which refers to the two dark lines along the flanks.

This feature is common to all members of the subgenus and can be used to clearly distinguish them. The two lines are often mood dependant though, often being vivid in males and juvenile females, but more variable with adult females. They are muted or completely absent in displaying adult males which instead have a kaleidoscope of iridescent colours across their flanks instead.

Whilst the species belonging to this subgenus are instantly identifiable as such, there is often large variability within, and between, each of them. Because of this, within the hobby they are described not just by their species name but also by collection location codes to ensure lines are maintained pure.

Chromaphyosemion bivittatum "Besingui" ADL 13-40 by William King

Getting started with Chromaphyosemion

Around 10 years ago I became aware of the lack of Chromaphyosemion spp. within the British Killifish Association (BKA). However, Aquabid had a tantalising number of eggs advertised which I could not resist for long; I inevitably bid on, and fortunately won, around six different species.

Chromaphyosemion volcanum "Kompina" CO3/14 by William King

The eggs were delivered soon after, which is the common way to share killifish with other hobbyists. I successfully hatched, reared, and then bred the resulting adults to create the next generation for both myself and to share within the community. This for me is the pinnacle of breeding killifish, and I will outline my methods should you wish to try this yourself. 

Chromaphyosemion Fact File

Size: Most species reach a maximum of 5 cm (2 in).

Origin: Coastal regions of West Africa.

Habitat: Shaded rainforest streams and ditches amongst leaf litter and aquatic plants.

Minimum tank size: 45 x  20 x 20 cm (18 x 8 x 8 in).

Water requirements: Soft to moderate hardness with a conductivity of 150-250us, pH is not critical anything from 6.6 to 7.4. 

Temperature: 18-25°C (64-77°F).

Temperament: They can be kept in a community tank with similar sized, non-aggressive fish. However, the real joy of keeping killifish is in breeding and raising the next generation. Chromaphyosemion are some of the easiest killifish to breed with minimal requirements but males can often drive females hard when breeding. It is therefore important to provide the female many hiding places with leaves, live/artificial plants or acrylic wool mops.

Feeding: They are micro-predators feeding mainly on terrestrial and aquatic insects. Any live food is preferred. They will eat good quality dried food/frozen food but egg production will be reduced

Availability & cost:  Rarely seen in stores but available via BKA auctions and online. Killifish are usually bought as pairs or trios (1 male, 2 females) for £10-£25. The resilient eggs can be posted usually costing £15-£25 for 20 eggs excluding the postage.

Chromaphyosemion volcanum ‘Kompina’ KV 03/21 by William King.

Breeding setup for Chromaphyosemion 

You do not need anything too elaborate to breed Chromaphyosemion.

Rainwater is my preferred choice but treated tap water can be used with good results, especially if your tap water has a fairly neutral pH, ideally between 6.8 and 7.2.

I don't use filtration, preferring instead to do frequent partial water changes of around one third of the tank volume every 10 days, using water that matches the same chemistry and temperature as the tank. Alternatively, a small air driven sponge filter works well to enable slightly smaller or less frequent water changes.

Temperature wise, I typically run my aquariums between 22 and 24°C (72–75°F).

A handful or two of pre-soaked coir covers the tank base as a substrate. You must ensure the coir you use is pure and does not have additives for plant growing! It is often sold as a substrate for reptile vivaria and is packaged as a dry block around the size of a house brick. When placed into water it will absorb water and expand, but as this takes some time, I always like to have some well-soaked coir in a dedicated bucket ready to go should I ever need it.

Ideally, once it is all fully submerged, carefully drain off the dark brown water produced by the release of tannins and replace with fresh rainwater (or dechlorinated tap water if this is your chosen source water). This lessens the brown-water effect in the tank, but you may wish to do this a couple of times if you want to further reduce the tint.

I also decorate the tank with two woollen spawning mops: one tied to a clean cork to float, and the other without a cork and submerged on the substrate.

Water movement and surface agitation is generated using an air pump and airline into the aquarium, giving a slow trickle of steady air. If this is too turbulent, I’ve found it can freak the fish out a little.

Related article: How do I breed these short-lived killifish?

Collecting the eggs

I have never had that much success with water incubation, with eggs often getting fungus on them and affecting the adjacent and otherwise healthy eggs. My preferred method is to place them on some damp (but not wet) coir.

I have many small, round, clear plastic containers for egg storage and incubation. They don’t need to be large; mine are around the size of a cupcake and are cheap to buy. They can be cleaned and used over and again, so for those trying to reduce their use of plastics, this is not single-use and, if you look after them, they’ll last a lifetime.

I put a small amount of squeezed coir into one, removing the excess water, and place eggs picked from the mops onto the coir. Should some eggs fungus, they are easily visible against the dark brown coir and can be removed quickly before it spreads.

The lid ensures the coir remains damp. If you feel the coir is drying out during the incubation period, use a pipette to add a few drops of warm water to restore the light moisture level, but don't overdo it.

Always remember to attach a label to the container with the species name and location code. It is also good practice to write the date the eggs were collected and the anticipated date for putting them in water for hatching. I typically allow 16–18 days from collection for the incubation period before submerging the eggs for hatching.

Hatching killifish

I like to use small acrylic boxes, intended for use in the kitchen, which are ideal for hatching purposes. I add some water, which should be the same temperature and water chemistry as the tanks that house the adults, before introducing the coir and eggs together.

Sometimes fry hatch within the hour; other times it takes a couple of days. Because eggs are typically collected over several days, they will always hatch in stages.

Fry need small food that is suitable for their tiny mouths, with vinegar eels, microworms, rotifers and paramecium all being great first foods.

Newly hatched brine shrimp is often too large for newly hatched fry, plus the size of it can vary depending on which eggs you have used and their age at the time of collection. The fry can normally take freshly hatched brine shrimp after a few days, though, so you can have this on standby.

Pay close attention to the initial feeding and work out how much they will eat. You don't want to starve them, but overfeeding can also be problematic. I still make the odd mistake after some 46 years of breeding killifish, so don't beat yourself up if you overdo it sometimes. Collecting eggs, hatching and rearing fry is quite a skill, and none of us are born knowing how to do it. We have to learn and, along the way, make mistakes.

The fry are notoriously slow growing, and it can be some four months or more before they can be considered young adults. You will get an idea of the sex ratio fairly early on, though, as the young males soon start to gain some faint colour in their fins.

Grindal worms - photo by Shutterstock

As they become larger, I start to feed some grindal worms and high-quality small granule dry food every few days, but sparingly until they get a taste for it. Brine shrimp is always my mainstay food for my killies, Nothobranchius included. They never tire of it!

Give your killifish plenty of variety in their diet. I also routinely offer them live Tubifex worms and frozen bloodworm, mostly for the adults given the larger size of these foods.

During the summer I collect mosquito larvae from rubber trugs in the garden. The tiny larvae are great food for growing fry, as are the larger larvae for adults. I can often find blackworm as well.

Chromaphyosemion splendopleure "Tiko Big Ikange Camp" 2002 by William King

Choosing a Chromaphyosemion killifish

There are currently 18 species within the Chromaphyosemion subgenus, which have varying degrees of availability within the hobby.

All species are between 4 and 5 cm (1.6 –2 in) in length as adults, except for Chromaphyosemion riggenbachi, which can reach over 7 cm (2.8 in) in length.

Amongst the eggs I originally bought via Aquabid were some of a species called Chromaphyosemion splendopleure ‘Tiko Big Ikang Camp’… quite a mouthful!

I believe I may well have been the first person in the United Kingdom to have these. I bred and reared at least a hundred fish, many of them making their way to auctions around the country.

They have a lovely green hue, and like all members of this subgenus, males can be a sight to behold when displaying to females.

With that in mind, all Chromaphyosemion males can be very colourful fish. I'd go as far to say they can rival many marine fish.

Sadly, when bagged up for auction they tend to lose much of their colour, and so people are unaware of their potential beauty and often fail to bid for them… losing out.

These fish are generally easy to maintain and breed, and are usually among the first killifish people new to the hobby will keep, for very good reasons.

There are a range of these stunning killifish kept and maintained by members of the British Killifish Association. 

This article was first published in the March 2025 issue of Practical Fishkeeping.